universe essay conclusion

Conclusion: The Universe Has a Cause of Its Existence

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• William Lane Craig  

Part of the book series: Library of Philosophy and Religion ((LPR))

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Since everything that begins to exist has a cause of its existence, and since the universe began to exist, we conclude, therefore, the universe has a cause of its existence. We ought to ponder long and hard over this truly remarkable conclusion, for it means that transcending the entire universe there exists a cause which brought the universe into being ex nihilo . If our discussion has been more than a mere academic exercise, this conclusion ought to stagger us, ought to fill us with a sense of awe and wonder at the knowledge that our whole universe was caused to exist by something beyond it and greater than it. 159 For it is no secret that one of the most important conceptions of what theists mean by ‘God’ is Creator of heaven and earth.

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© 1979 William Lane Craig

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Craig, W.L. (1979). Conclusion: The Universe Has a Cause of Its Existence. In: The Kalām Cosmological Argument. Library of Philosophy and Religion. Palgrave Macmillan, London. https://doi.org/10.1007/978-1-349-04154-1_9

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Universe: essay on our universe | geography.

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Here is an essay on ‘ Our Universe’ for class 6, 7, 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Our Universe’ especially written for school and college students.

Essay on Our Universe

Our Universe contains 176 billion (one billion = 100 crores) constellations (group of stars) and each constellation includes hundreds of billion stars. Universe consists, constellation, in which Sun exists, is so big that from the core of constellation, light takes around 27 thousand years to reach up to sun. The solar system which is part of Milky Way galaxy is in disc-shaped spiral form.

Essay # 1. Sun:

Sun rotates round its axis from West to East. About 99.85% mass of solar system lies with sun only whereas planets constitute – 0.135%, comets – 0.01%, satellites – 0.00005%, dwarf planets – 0.000002%, shooting stars – 0.0000001% and inter planetary medium consists of 0.0000001% of the rest of mass.

Sun is not stationery and completes one rotation round its own axis in 25 days. One rotation of sun takes 25 days (of Earth) if observed from the equator while if we observe it from its poles, each rotation of sun takes 36 days. The rotation of sun was observed by Galileo first of all.

Sun is source of light, heat, energy and life on our Earth. Normally looking pale, this spherical ball of fire has 13 lakh multiples more volume than that of Earth and 3.25 lakh times more weight. Pressure of gaseous material on its centre is 200 billion multiples more than the pressure of air, Earth experiences while density of gases is 150 times more than that of water. Temperature of sun is 50 lakh degrees Kelvin (one Kelvin is equal to one degree on Celsius scale).

Hydrogen in form of Plasma turns into Helium at this temperature. This fusion gives birth to energy. The quantum of such produced energy may be imagined from the fact that fusion produced energy in one second is more than as much mankind has used on Earth till date. This fusion is continuous process on the surface of Sun.

Gravity of Sun is 28 times more than that of earth and black spots visible on sun are actually very powerful magnetic regions. Each magnetic regions of sun is more than 10 thousand times more powerful than magnetic power of Earth. Actual size of each black spot may be lakhs of square kilometers. Temperature at photosphere of sun is only 6000° Kelvin while ends of chromospheres experience it 10 thousand degree.

At corona this temperature varies from 10 lakh Kelvin to 50 lakh Kelvin. Continuous winds blow at the surface of sun at speed of 800 to 900 kilometer per second and these may prove dangerous for Earth at times. These winds have their fatal effect on Ionosphere. Solar storms disturb communication system on Earth. Many a times, power grids get destroyed or seized because of disturbance at the surface of Sun.

Optical telescope at Udaipur and Kodyekanal along with Radio telescope at Pune keep continuous watch over happenings related to Sun.

Essay # 2. Planets:

Planet is a Greek word which means, Wanderer. All the planets are spherical and are total eight in number.

We can group these planets in two, that is:­

a. Inner Planets:

Inner planets are those planets which are nearer to sun as compared to others. Secondly their relief constitution includes rocks and metals. These planets are known as terrestrial planets also. Namely these planets are; Mercury, Venus, Earth & Mars.

b. Outer Planets:

Outer planets are beyond asteroids and are constituted of gases, popularly known as Gas Giants. These are; Jupiter, Saturn, Uranus and Neptune.

The planets do not have any light of their own but these illuminate by reflecting sunlight and are visible at night. In the sequence of their distance from sun, these may be retented from initial alphabets of words in this sentence; My Very Efficient Mother Just Served Us Nuts.

i. Mercury:

This planet is not only smallest one but also lies closest to Sun. It does not have atmosphere of its own and is engulfed by blasts taking place because of Sun. Its core is made of iron and has this part larger than crust.

It is presumed that this crust reduced due to some comet accident. Mercury lies some 579 million (57crore 90 lakh) kilometer away from Sun and its average temperature varies between 420°C during day to -180°C at night.

It completes its revolution around Sun in 88 days while takes 58 days and 16 hours to complete its one rotation on its axis. Galileo founded Mercury in 1631 which has no satellite.

This is a rocky celestial body like Earth and second planet if counted serial vise from Sun. It completes its revolution round sun is 224.7 days while takes 243 long days to complete its rotation round its own axis from East to West.

All the other planets rotate around their axis from West to East. This hottest planet is second most glittering celestial body, first being the Moon. Also known as sister planet of Earth, Venus resembles to it in shape, size and gravity.

It has a number of volcanoes just like Earth and its surface has been formed because of volcanic eruptions. Its atmosphere consists of Carbon dioxide (96.5%) and Nitrogen. That is why it is called ‘Veiled planet’ also. Venus lies nearly 1082 million kilometers away from Sun.

iii. Earth:

Our mother planet’s name has not been derived from Greek or Roman language but from old English and Germanic. According to International Astronomical Union (IAU) biggest among Inner planets, Earth is only planet which has Geological activity taking place in its core.

Its atmosphere is also quite different to that of other planets as it consists of 77% Nitrogen and 21% Oxygen which gives it a name of ‘blue planet’. Earth is only planet where life exists. Situated nearly 14.96 crore kilometers away from sun.

The earth completes a rotation round its axis in 23 hours, 56 minutes and 4.09 seconds (approximately 24 hours) while to revolve around the sun, it takes 365 days 5 hours and 48 minutes. It has a satellite named Moon.

Known as the Red Planet, Mars is fourth planet of our solar system as counted from Sun. Its soil has very rich iron content and because of Ferrus content it looks red. As far its rotation on axis is concerned, it has similarity with Earth and it supports various seasons also.

Mars is a cold planet which has thin atmosphere. Its one rotation on its axis is completed in 24 hours, 37 minutes and 23 seconds while its revolution against sun takes 687 days. Having two satellites, Mars is placed around 2279 lakh kilometer away from sun.

The success of India to plant its Orbiter in orbit of Mars in its just first attempt has made it a pioneer and an exceptional one. Mars is only planet other than Earth which has ice-caps on its poles which have been named as Planum Boreum (North Pole) and Planum Australe (South Pole) or Southern Cap. The spacecraft that reached in the orbit of Mars is named 440 Newton Liquid Apogee Motor (LAM).

v. Jupiter:

First beyond the Asteroids, Jupiter is fifth planet of our solar system and is the biggest planet. This planet is one of the Gas Giants and has 1280 kilometer wide atmosphere composed of gases like Methane, Ammonia, Hydrogen and Helium.

It revolves around the sun in anti-clockwise direction and completes one revolution in 12 years. Its rotation on its axis is very fast and completes one in just 10 hours causing severely blowing winds.

These winds look like multi-coloured cloud belts. Jupiter is tilted on its axis at 3.1° and has more than 60 satellites. Most of the satellites are unknown for mankind as far information about them is concerned.

vi. Saturn:

The sixth from sun and second largest planet in solar system is Saturn. Situated some 1,431 million kilometers (More than 143 crore km) away from Sun, it is constituted of iron and nickel principally. Completing its rotation on its axis in 10 hours and 41 minutes, it makes one revolution around Sun in 29.5 years.

Its swift rotation gives rise to winds at the speed of 1800 kilometers per hour. Speed of winds on Saturn is higher than that on Jupiter but lesser than that on Neptune. There are nine rings around Saturn which from three arcs around it. These rings are made of frozen ice and rocks. It has around 62 satellites and biggest among them is Titan which is almost double the size of Moon. The atmosphere of Titan is thicker than that of Earth.

vii. Uranus:

This is seventh planet of our Solar System and third largest planet. Its size is 63 multiples bigger than earth but in weight it is only 14.5 multiples than that of Earth. Constituted of gases, Uranus has coldest atmosphere as compared to all the planets and has an average temperature of 223°C. Many layers of clouds are found on Uranus.

Higher cloud formation consists of Methane gas while lower formation consists of water. Speed of winds on this planet is 250 meters per second while it is tilted at 97.77° on its axis. Revolving round sun in anti-clockwise direction, it completes one revolution in 84 years while for completing one rotation around its axis, it takes 10 hours and 48 minutes.

viii. Neptune:

Neptune resembles to Uranus as seen in the Solar System. But it is smaller than Uranus and its surface is more condense. Presence of Methane gas makes it look green. Winds blow at speed of 2100 kilometers per hour in the atmosphere of this planet.

The planet consists of around 900 full circles and various incomplete arcs. Situated approximately 4,498 million kilometer away from Sun, it completes one rotation its axis in 16 hours and a revolution around sun in 164.8 years. Neptune has 13 satellites while Triton and Neried are two main satellites.

There are various dwarf planets in our solar system, out of which only five have been recognised.

1. Pluto (Earlier know as ninth planet, was declared dwarf in August, 2006)

4. Make make

Essay # 3. Satellites:

Satellites are of two types, manmade and natural. Satellites are actually celestial objects that revolve around some other celestial object. Natural satellites rotate on their axis also. They neither have atmosphere nor light of their own but due to reflection of sunlight, they look illuminated.

Manmade satellites are made of aluminium or plastic and are hardened with help of carbonic sheets. They travel at the speed which is 10 to 30 multiples more than that of an aircraft. Humankind has been benefitted extremely by manmade satellites in fields of telecommunications, weather forecasting, geological activities and atmospheric activities among other fields. India fired its first satellite named Arya Bhatt in 1975 and since then, we have sent more than 75 satellites into the orbit.

Moon is natural satellite of our Earth. It is around 3,84,403 kilometers away from Earth and takes 27.3 days to complete its revolution around Earth. As yet mankind has touched only this celestial body i.e. Moon on 21st July 1969. Atmosphere of Moon is so thin that it weighs only 104 kilograms and gravity is only one sixth part of the gravity of Earth.

Essay # 4. Asteroids or Planetoids:

These are too smaller than planets of Solar System but bigger than Asteroids. These celestial bodies revolve round the sun in anti-clockwise direction. These rocky bodies are numerous and most of these are concentrated between Mars and Jupiter. Five of them namely Ceres, Pallas, Vesta, Hypiea and Euphrosyne have been recognised. European Space Agency has found water vapour on Ceres on 22nd January, 2014.

Essay # 5. Comets:

The word comet is derived from Latin word ‘Stella Cometa’ which means ‘hairy star’. These celestial bodies were part of sun earlier and are made of frozen gases, ice and small rocky substances. Head of comet is 16 million kilometers in diameter and is followed by cloud of misty substance looking like a tail.

This tail is also lakhs of kilometer long. Tail is never towards sun facing side of comet and shines with rays from Sun. Comet which passed through Solar System was first seen in 1705 and it passes close to sun after every 75.5 years. English scientist Edmond Halley founded it and it was therefore named Halley’s Comet.

Comets are being traced regularly. Their total number was 5,186 in August, 2014. Halley’s Comet was seen in 1910, then in 1986 and next it shall be sighted in 2062. Nucleus of Halley’s Comet is 16 x 8 x 8 kilometers and it is the darkest object in solar system. This comet is periodical one and may be sighted at specific intervals but all the comets are not periodical.

Essay # 6. Meteors or Meteorites:

One can see a streak of star light in the sky sometimes, it gives an impression that any part of star has broken away. These are actually meteorites. Parts of meteorites that remain unburnt and reach our Earth in small parts are named as meteorites.

When these enter the atmosphere of Earth, burn out immediately and vanish in shape of ash most of times. A part of Arizona desert in U.S. is known to have come into form due to striking of some meteor. There are, however, various principles about formation of meteors. Some thinkers part them parts of planet which has vanished while others say these are parts of Sun, Earth and Moon only.

Indian Museum at Kolkata is known for preserving remains of meteors. Biggest such museum in Asia, it has 468 meteor parts. Their study has concluded that meteors are made of metals like iron, nickel, aluminium, oxygen and tin.

These get attracted towards Earth because of gravity of Earth. On April 21, 2013 a meteor shower was observed in many parts of the world in which more than 20 shooting stars were seen within an hour. This shower is known as Orionid Meteor Shower. Such wonderful sights are very common in our solar system.

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Situation Critical Fall 2016

Between Humans and the Universe: All We Have are the Connections We Make

What do we do with the universe.

“Wonder is the beginning of all wisdom,” says Aristotle in Metaphysics . “And looking into the starry sky is the beginning of wonder,” say I.

Andrew Yang starts his Interviews with the Milky Way by asking his mother, Ellen,

“ When you were a child, did you ever look up at the stars?”

For Ellen, childhood has long departed, as the moon has dyed all her hair. However, she answers with the greatest clarity,

“ Oh yes, oh yes,” she replies, “we were trying to see the milky way.”

Gazing into the sky and wondering about the universe is not an experience limited to any one generation. Andrew makes it clear that it is so profoundly shared by human beings that it almost becomes an instinct. Later in the interview, he talks about his daughter, Stella, who asks him since the outer space is above the sky, what is above the outer space.

The directional and intentional gaze into the night sky, then, is our first conscious encounter with the universe. Because of the gaze, the universe enters our sight and our mind. Now, it does not only objectively exist, but also exists to us .

In our galaxy, there are at least 100 billion stars. In an infant, hydrogen makes up 9.5% of its body weight, carbon, 18.5%, and oxygen, 65%. In A Beach and All Things Being Equal , we are educated of these pieces of information.

While it is true that wisdom starts with wonder, it does not end with wonder. Instead, we study and seek answers to our wonders. Just like Jeff, an astrophysicist says in Interviews with the Milky Way , “The most important thing you know about the universe is that, it is comprehensible.” That is, we can know about the universe.

After we gaze at things in the universe, we name them, analyze them, and attach information to the names. As a result, we pin the things down, and “know” the universe. In other words, things in the universe do not disappear or get lost as we move our eyes away, but are captured by us because we “know” them, just as Andrew makes a beach of 100 billion grains of sand, and just as he lists the chemical component of his daughter.

We Identify

In All Things Being Equal , tap water, rock sugar, canola oil, powdered L-Arginine, three oyster shells, baking powder and vinyl are placed in seven glass containers. According to a calculation next to the piece, these object and Andrew’s daughter, the new-born Stella share 99% of chemical elements.

In The Way Within , we see a table of objects ranging from a rock to a juice container, from a shell fish to a Ming lock, and from maple leaves to Lego pieces. All objects are mild in color, with pale turquoise on one side of the table, and blanched almond on another. When placed together, they display a surprising unity. At a point, you feel they are more similar than different because of their color, shape, size, and even the vibes they are giving out, and the distinction between “natural” and “man-made,” between “nature” and “culture” starts to seem arbitrary.

In Interviews with the Milky Way , Jeff agrees that he sometimes “thinks of himself as the Milky Way,” whereas Ellen calls the Milky Way “the ultimate life giving entity,” that is, a mother just like herself.

As we gather more facts and know more about the universe, we naturally form feelings about it and express them. Andrew’s art is one such example, announcing this sense of identification:

Our bodies are similar to the bodies of other galactic matters. Our products of culture are similar to the products of nature. We are similar to the universe.

All We Have are the Connections We Make

Andrew’s project walks us through what we do with the universe, from gazing, to knowing, to identifying. The underlying and overarching in all three becomes more evident as we go further. That is, they are all ways in which we connect with the universe, and one deeper than another.

By gazing, we connect. We stretch the invisible line between our eyes and the object, and realize not only we ourselves exist, other things in the universe, too, exist. That is, we share the time and space with objects in the universe.

By knowing, we connect. We use the human faculty to understand, so that objects reside in our minds as ideas. That is, we incorporate as part of us the objects in the universe.

By identifying, we connect. We acknowledge shared natures we have with objects in the universe. That is, we are the objects in the universe.

Andrew’s project not only reminds us of these connections, but also their importance. Being vast and grand, the universe does not intimidate us mortal beings. Instead, it empowers us. On the one hand, we are promised of knowledge, that we can know things beyond ourselves. Jeff says that because studying the universe makes him realize he is able to contemplate about things beyond himself and beyond people, it gives him a sense of “wellbeing.” On the other hand, we are assured of company, that we are not the lonely powerless beings, but have connections to something eternal. Ellen says that when she dies, rather than going to the heaven, she would prefer to be attached to a star, and that would make her “feel better.”

In other words, through the connections with the universe, we are able to obtain knowledge and feel that we belong, both conducive to happiness. And happiness, according to Aristotle, is the ultimate human end.

To Connect, to Connect Deeper

The project, however, is not just a reminder. Instead, it encourages, and even urges us to actively make these connections ourselves because these connections do not necessarily come naturally. As Ellen remarks, “Where I lived the sky was clear. You could see stars. But when [Stella] looks into the sky, she sees something entirely different than I did at the same age.” Andrew addresses the issue that light pollution denies access to the night sky from urban dwellers, and creates A Beach to “substitute” the Milky Way. The installation of seven tons of sand, although of course not the Milky Way, pushes the urban dwellers who go into the dim room filled with white noise to think of the Milky Way, and identify with the Milky Way.

Also, Andrew is inspiring his audience to make deeper connections with the universe. Whereas science gathers facts and data, art arouses human emotions, thus striking directly at the core of human soul. With science, we can know the chemical component of a human infant and of the inanimate objects in the universe. However, when Andrew juxtaposes the two in All Things Being Equal , he sets the example that art brings the connection of “knowledge” to the higher level of connection, that is the connection of “identification,” leaving a stronger impression and impact on the audience.

The project is utterly beautiful. I have often wondered why at the moments when we look up into the sky, when it cannot be clearer that we are small and we are mortal, we rarely feel worthless. Andrew seems to be providing this poetic answer: Through a gaze, and starting from the gaze, we make connections with the universe. We become part of it, we get to know it, and we become it. Saved by a gaze, we are not at all small, not at all mortal, and not at all worthless.

1,274 Comments

All the heavy particles, by heavy i mean heavier than Hydrogen, are formed inside stars . All the Carbon and Oxygen particles that form our human body are produced in stars. We have this natural connection . We are the product of star fusion.

That’s fascinating :3

Thank you for sharing

We are made of stars, so please shine.

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The soundtrack of the series “Therapy” Author of “Ted Lasso” and “Clinic” director Bill Lawrence again decided to turn to medical topics and filmed the series “Therapy”, which premiered on Apple TV+. Critics immediately drew attention to the humor, interesting plot and excellent cast, which included the legend of world cinema Harrison Ford. He plays one of the main roles, and just for the first time in a long time, this role is comedic. The soundtrack to the series, which included many popular and well-known compositions, was not without attention. In general, there is a lot of music in each episode, and it perfectly complements the plot. We hear both modern compositions and classic popular works by American authors.

Paito Hongkong

Your critique is stunning. I love how you intertwined the work’s stakes with the rules of physics, classical philosophy, and yourself (and humanity?). Your emphasis on connection was particularly powerful. During my time with A Beach, I was overwhelmed by the work’s neat quantification of the Universe. But your emphasis on connection speaks to both wonder and intimacy. Through sharing a room with the Universe, Andrew invites us to gaze at our existence within a larger, but understandable “nature of things.”

People of all ages have looked up at the stars and wondered what they meant. Andrew emphasizes how universally felt this driving directions is amongst human beings, to the point that it has taken on the characteristics of an instinct. Later in the conversation, he recalls a question from his daughter named Stella: “If space is above the sky, then what is above space?”

This is a truly magnificent critique that transcends mere analysis. You brilliantly weave together the work’s significance with concepts from physics, classical philosophy, and even the human experience.

Your emphasis on connection is particularly powerful and insightful. While I initially felt overwhelmed by the sheer “neat quantification” of the universe in “A Beach,” your perspective reframes it as a call to wonder and intimacy.

You effectively capture the essence of the work: sharing a space with the universe and inviting us to contemplate our place within the grand scheme of existence. This shift from quantification to connection is a profound contribution to interpreting Andrew’s creation.

Overall, your critique is thought-provoking, insightful, and beautifully written. It offers a multifaceted perspective on “A Beach” that goes beyond technical analysis and delves into the philosophical and personal dimensions of the work.

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Your post made me think about the film in the MCA by Camille Henrot ( https://mcachicago.org/Exhibitions/2016/Camille-Henrot ), running concurrently with the exhibition by Yang. Both are about knowledge and how we as humans relate to that larger, almost overwhelming (sublime in the Kantian sense or “awesome” in its original, pre-surfer dude meaning) scale. One sees the interests of Joey Orr as curator here. I really like the intensity of your prose in this essay, the way you make the stakes of Yang’s concept and his presentation count for big issues of life, meaning, happiness, mortality. Here’s one thing I wonder too: is there also a bit of humor in Yang’s work? A sweet kind of funniness? Prof. Kramer

Lovely essay. The mystery of the universe continues with an ever-present wonder. This is the only way it will ever be for humankind. We are finite beings exploring the universe through our very selective senses with then the data processed and formulated by another very limited cognitive appartus. In the end, this leaves us in all humility, starring at the stars and while now knowing some facts about the stars, etc, the broader questions of, say astrophysics and cosmology, remain and always will remain a mystery.

Lovely …. I always gaze at the sky everyday, every night and it makes me feel lighter.

I love my true friend Brett Laudato, the only love in my life.

He is in my opinion also a scientist. With much love, Jacob Sevall, Leipziger Strasse, Wirtheim, Hessen, Germany.

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The Search for Life in the Universe

By Neil deGrasse Tyson

Natural History Magazine

September 1996

Published under the title “Is Anyone Out There Like Us?”

To declare that Earth is the only planet in the universe with life would be inexcusably bigheaded of us.

The recent discovery of about half a dozen planets around stars other than the Sun has triggered tremendous public interest. Attention was driven not so much by the discovery of extra-solar planets, but by the prospect of them hosting intelligent life. In any case, the media frenzy that followed was somewhat out of proportion with the events. Why? Because planets cannot be all that rare in the universe if the Sun happens to have a bunch of them. Also, the newly discovered planets are all oversized gaseous giants that resemble Jupiter, which means no convenient surface exists upon which life as we know it could live. And even if they were teeming with buoyant aliens, the odds against these life forms being intelligent may be astronomical.

Ordinarily, there is no riskier step that a scientist (or anyone) can take than to make sweeping generalizations from just one example. At the moment, life on Earth is the only known life in the universe, but there are compelling arguments to suggest we are not alone. Indeed,  most astrophysicists accept the probability of life elsewhere. The reasoning is easy: if our solar system is not unusual, then there are so many planets in the universe that, for example, they outnumber the sum of all sounds and words ever uttered by every human who has ever lived. To declare that Earth must be the only planet in the universe with life would be inexcusably bigheaded of us.

Many generations of thinkers, both religious and scientific, have been led astray by anthropocentric assumptions, while others were simply led astray by ignorance. In the absence of dogma and data, it is safer to be guided by the notion that we are not special, which is generally known as the Copernican principle, named for the Polish astronomer Nicholas Copernicus who, in the mid 1500s, put the Sun back in the middle of our solar system where it belongs. In spite of a third century BC account of a sun-centered universe (proposed by the Greek philosopher Aristarchus), the Earth-centered universe was by far the most popular view for most of the last 2,000 years. Codified by the teachings of Aristotle and Ptolemy, and the preachings of the Roman Catholic Church, people generally accepted Earth as the center of all motion. It was self evident: the universe not only looked that way, but God surely made it so.

While there is no guarantee that the Copernican principle will guide us correctly for all scientific discoveries to come, it has revealed itself in our humble realizations that not only is Earth not in the center of the solar system, but the solar system is not in the center of the Milky Way galaxy, and that the Milky Way galaxy is not in the center of the universe. And in case you are one of those people who thinks that the edge may be a special place, then we are not at the edge of anything either.

A wise contemporary posture would be to assume that life on Earth is not immune to the Copernican principle. If so, then how can the appearance or he chemistry of life on Earth provide clues to what life might be like elsewhere in the universe?

I do not know whether biologists walk around every day awestruck by the diversity of life. I certainly do. On this single planet called Earth, there coexist (among countless other life forms), algae, beetles, sponges, jellyfish, snakes, condors, and giant sequoias. Imagine these seven living organisms lined up next to each other in size-place. If you didn’t know better, you would be hard-pressed to believe that they all came from the same universe, much less the same planet. Try describing a snake to somebody who has never seen one:  You gotta believe me. There is this animal on Earth that 1) can stalk its prey with infrared detectors, 2) swallows whole live animals up to five times bigger than its head, 3) has no arms or legs or any other appendage, yet 4) can slide along level ground at a speed of two feet per second!

Given the diversity of life on Earth, one might expect a diversity of life exhibited among Hollywood aliens. But I am consistently amazed by the film industry’s lack of creativity. With a few notable exceptions such as life forms in The Blob (1958) and in 2001: A Space Odyssey (1968), Hollywood aliens look remarkably humanoid. No matter how ugly (or cute) they are, nearly all of them have two eyes, a nose, a mouth, two ears, a head, a neck, shoulders, arms, hands, fingers, a torso, two legs, two feet—and they can walk. From an anatomical view, these creatures are practically indistinguishable from humans, yet they are supposed to have come from another planet. If anything is certain, it is that life elsewhere in the universe, intelligent or otherwise, will look at least as exotic as some of Earth’s own life forms.

The chemical composition of Earth-based life is primarily derived from a select few ingredients. The elements hydrogen, oxygen, and carbon account for over 95 percent of the atoms in the human body and all known life. Of the three, the chemical structure of carbon allows it to bond readily and strongly with itself and with many other elements in many different ways, which is why we are considered to be carbon-based life, and which is why the study of molecules that contain carbon is generally known as  organic  chemistry. Curiously, the study of life elsewhere in the universe is known as exobiology, which is one of the few disciplines that attempts to function with the complete absence of first-hand data.

Is life chemically special? The Copernican principle suggests that it probably isn’t. Aliens need not look like us to resemble us in more fundamental ways. Consider that the four most common elements in the universe are hydrogen, helium, carbon, and oxygen. Helium is inert. So the three most abundant, chemically active ingredients in the cosmos are also the top three ingredients in life on Earth. For this reason, you can bet that if life is found on another planet, it will be made of a similar mix of elements. Conversely, if life on Earth were composed primarily of, for example, molybdenum, bismuth, and plutonium, then we would have excellent reason to suspect that we were something special in the universe.

Appealing once again to the Copernican principle, we can assume that the size of an alien organism is not likely to be ridiculously large compared with life as we know it. There are cogent structural reasons why you would not expect to find a life the size of the Empire State Building strutting around a planet. But if we ignore these engineering limitations of biological matter we approach another, more fundamental limit. If we assume that an alien has control of its own appendages, or more generally, if we assume the organism functions coherently as a system, then its size would ultimately be constrained by its ability to send signals within itself at the speed of light—the fastest allowable speed in the universe. For an admittedly extreme example, if an organism were as big as the entire solar system (about 10 light-hours across), and if it wanted to scratch its head, then this simple act would take no less than 10 hours to accomplish. Sub-slothlike behavior such as this would be evolutionarily self-limiting because the time since the beginning of the universe may be insufficient for the creature to have evolved from smaller forms of life over many generations.

How about intelligence? When Hollywood aliens manage to visit Earth, one might expect them to be remarkably smart. But I know of some that should have been embarrassed at their stupidity. During a four-hour car trip from Boston to New York City, while I was surfing the FM dial, I came upon a radio play in progress that, as best as I could determine, was about evil aliens that were terrorizing Earthlings. Apparently, they needed hydrogen atoms to survive so they kept swooping down to Earth to suck up its oceans and extract the hydrogen from all the H 2 O molecules. Now those were some dumb aliens. They must not have been looking at other planets en route to Earth because Jupiter, for example, contains over 200 times the entire mass of Earth in pure hydrogen. I guess nobody ever told them that over 90 percent of all atoms in the universe are hydrogen.

And how about all those aliens that manage to traverse thousands of light years through interstellar space, yet bungle their arrival by crash-landing on Earth?

Then there were the aliens in the 1977 film Close Encounters of the Third Kind, who, in advance of their arrival, beamed to Earth a mysterious sequence of repeated digits that were eventually decoded to be the latitude and longitude of their upcoming landing site. But Earth longitude has a completely arbitrary starting point—the prime meridian—which passes through Greenwich, England by international agreement. And both longitude and latitude are measured in peculiar unnatural units we call degrees, 360 of which are in a circle. Armed with this much knowledge of human culture, it seems to me that the aliens could have just learned English and beamed the message,  We’re going to land a little bit to the side of Devil’s Tower National Monument in Wyoming. And since we’re coming in a flying saucer we won’t need the runway lights.

The award for dumbest creature of all time must go to the alien from the original 1983 film Star Trek, The Motion Picture.  V-ger , as it called itself (pronounced vee-jer) was an ancient mechanical space probe that was on a mission to explore and discover and report back its findings. The probe was “rescued” from the depths of space by a civilization of mechanical aliens and reconfigured so that it could actually accomplish this mission for the entire universe. Eventually, the probe did acquire all knowledge and, in so doing, achieved consciousness. The Star Trek crew come upon this now-sprawling monstrous collection of cosmic information at a time when the alien was searching for its original creator and the meaning of life. The stenciled letters on the side of the original probe revealed the characters  V  and  ger . Shortly thereafter, Captain Kirk discovers that the probe was  Voyager 6 , which had been launched by humans on Earth in the late twentieth century. Apparently, the  oya  that fits between the  V  and the  ger  had been badly tarnished and was unreadable. Okay. But I have always wondered how  V-ger  could have acquired all knowledge of the universe and achieve consciousness yet not know that its real name was  Voyager .

And don’t get me started on the recently released summer blockbuster Independence Day. I find nothing particularly offensive about evil aliens. There would be no science fiction film industry without them. The aliens in Independence Day were definitely evil. They looked like a genetic cross between a Portuguese Man of War jelly fish, a hammer-head shark, and a human being. While more creatively conceived than most Hollywood aliens, why are their flying saucers equipped with upholstered high-back chairs with arm rests?

I’m glad that, in the end, the humans win. We conquer the Independence Day aliens by having a Macintosh laptop computer upload a software virus to the mothership (which happens to be ⅕ the mass of the Moon), which disarms its protective force field. I don’t know about you, but I have trouble just uploading files to other computers within my own department, especially when the operating systems are different. There is only one solution. The entire defense system for the alien mothership must have been powered by the same release of Apple Computer’s system software (version 7.5.2) as the laptop computer that delivered the virus.

Thank you for indulging me. I had to get it all off my chest.

Let us assume, for the sake of argument, that humans are the only species in the history of life on Earth to evolve high-level intelligence. (I mean no disrespect to other big-brained mammals. While most of them cannot do astrophysics, my conclusions are not substantially altered if you wish to include them.) If life on Earth offers any measure of life elsewhere in the universe, then intelligence must be rare. By some estimates, there have been more than ten billion species in the history of life on Earth. It follows that among all extraterrestrial life forms we might expect no better than about one in ten billion to be as intelligent as we are, not to mention the odds against the intelligent life having an advanced technology  and  a desire to communicate through the vast distances of interstellar space.

On the chance that such a civilization exists, radio waves would be the communication band of choice because of their ability to traverse the galaxy unimpeded by interstellar gas and dust clouds. But humans on Earth have only understood the electromagnetic spectrum for less than a century. More depressingly put, for most of human history, had aliens tried to send radio signals to earthlings we would have been incapable of receiving them. For all we know, the aliens have already done this and unwittingly concluded that there was no intelligent life on Earth. They would now be looking elsewhere. A more humbling possibility would be if aliens had become aware of the technologically proficient species that now inhabits Earth, yet they had drawn the same conclusion.

Our life-on-Earth bias, intelligent or otherwise, requires us to hold the existence of liquid water as a prerequisite to life elsewhere. A planet’s orbit should not be too close to its host star, otherwise the temperature would be too high and the planet’s water content would vaporize. The orbit should not be too far away either, or else the temperature would be too low and the planet’s water content would freeze. In other words, conditions on the planet must allow the temperature to stay within the 180 degree (Fahrenheit) range of liquid water. As in the three-bowls-of-food scene in the fairy tale Goldilocks and the Three Bears, the temperature has to be just right. When I was interviewed about this subject recently on a syndicated radio talk show, the host commented,  Clearly, what you should be looking for is a planet made of porridge!

While distance from the host planet is an important factor for the existence of life as we know it, other factors matter too, such as a planet’s ability to trap stellar radiation. Venus is a textbook example of this “greenhouse” phenomenon. Visible sunlight that manages to pass through its thick atmosphere of carbon dioxide gets absorbed by Venus’s surface and then re-radiated in the infrared part of the spectrum. The infrared, in turn, gets trapped by the atmosphere. The unpleasant consequence is an air temperature that hovers at about 900° Fahrenheit, which is much hotter than we would expect knowing Venus’s distance to the Sun. At this temperature, lead would swiftly become molten.

The discovery of simple, unintelligent life forms elsewhere in the universe (or evidence that they once existed) would be far more likely and, for me, only slightly less exciting than the discovery of intelligent life. Two excellent nearby places to look are the dried riverbeds of Mars, were there may be fossil evidence of life from when waters once flowed, and the subsurface oceans that are theorized to exist under the frozen ice layers of Jupiter’s moon Europa. Once again, the promise of liquid water defines our targets of search.

Other commonly invoked prerequisites for the evolution of life in the universe involve a planet in a stable, nearly circular orbit around a single star. With binary and multiple star systems, which comprise about half of all “stars” in the galaxy, planet orbits tend to be strongly elongated and chaotic, which induces extreme temperature swings that would undermine the evolution of stable life forms. We also require that there be sufficient time for evolution to run its course. High-mass stars are so short-lived (a few million years) that life on an Earth-like planet in orbit around them would never have a chance to evolve.

The set of conditions to support life as we know it are loosely quantified though what is known as the Drake equation, named for the American astronomer Frank Drake (now at the University of California at Santa Cruz). The Drake equation is more accurately viewed as a fertile idea rather than as a rigorous statement of how the physical universe works. It separates the overall probability of finding life in the galaxy into a set of simpler probabilities that correspond to our preconceived notions of the cosmic conditions that are suitable for life. In the end, after you argue with your colleagues about the value of each probability term in the equation, you are left with an estimate for the total number of intelligent, technologically proficient civilizations in the galaxy. Depending on your bias-level, and your knowledge of biology, chemistry, celestial mechanics, and astrophysics, you may use it to estimate from at least one (we humans) up to millions of civilizations in the Milky Way.

If we consider the possibility that we may rank as primitive among the universe’s technologically competent life forms—however rare they may be—then the best we can do is keep alert for signals sent by others because it is far more expensive to send rather than receive them. Presumably, an advanced civilization would have easy-access to an abundant source of energy such as its host star. These are the civilizations that would be more likely to send rather than receive. The search for extraterrestrial intelligence (affectionately known by its acronym SETI) has taken many forms. The most advanced efforts today uses a cleverly designed electronic detector that monitors, in its latest version, billions of radio channels in search of a signal that might rise above the cosmic noise.

The discovery of extraterrestrial intelligence, if and when it happens, will impart a change in human self-perception that may be impossible to anticipate. My only hope is that every other civilization isn’t doing exactly what we are doing because then everybody would be listening, nobody would be receiving, and we would collectively conclude that there is no other intelligent life in the universe.

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The Universe, Expanding Beyond All Understanding

By Dennis Overbye

• June 5, 2007

When Albert Einstein was starting out on his cosmological quest 100 years ago, the universe was apparently a pretty simple and static place. Common wisdom had it that all creation consisted of an island of stars and nebulae known as the Milky Way surrounded by infinite darkness.

We like to think we’re smarter than that now. We know space is sprinkled from now to forever with galaxies rushing away from one another under the impetus of the Big Bang.

Bask in your knowledge while you can. Our successors, whoever and wherever they are, may have no way of finding out about the Big Bang and the expanding universe, according to one of the more depressing scientific papers I have ever read.

If things keep going the way they are, Lawrence Krauss of Case Western Reserve University and Robert J. Scherrer of Vanderbilt University calculate, in 100 billion years the only galaxies left visible in the sky will be the half-dozen or so bound together gravitationally into what is known as the Local Group, which is not expanding and in fact will probably merge into one starry ball.

Unable to see any galaxies flying away, those astronomers will not know the universe is expanding and will think instead that they are back in the static island universe of Einstein. As the authors, who are physicists, write in a paper to be published in The Journal of Relativity and Gravitation, “observers in our ‘island universe’ will be fundamentally incapable of determining the true nature of the universe.”

It is hard to count all the ways in which this is sad. Forget the implied mortality of our species and everything it has or has not accomplished. If you are of a certain science fiction age, like me, you might have grown up with a vague notion of the evolution of the universe as a form of growing self-awareness: the universe coming to know itself, getting smarter and smarter, culminating in some grand understanding, commanding the power to engineer galaxies and redesign local spacetime.

Instead, we have the prospect of a million separate Sisyphean efforts with one species after another pushing the rock up the hill only to have it roll back down and be forgotten.

Worse, it makes you wonder just how smug we should feel about our own knowledge.

“There may be fundamentally important things that determine the universe that we can’t see,” Dr. Krauss said in an interview. “You can have right physics, but the evidence at hand could lead to the wrong conclusion. The same thing could be happening today.”

The proximate culprit here is dark energy, which has been responsible for much of the bad news in physics over the last 10 years. This is the mysterious force, discovered in 1998, that is accelerating the cosmic expansion that is causing the galaxies to rush away faster and faster. The leading candidate to explain that acceleration is a repulsion embedded in space itself, known as the cosmological constant. Einstein postulated the existence of such a force back in 1917 to explain why the universe didn’t collapse into a black hole, and then dropped it when Edwin Hubble discovered that distant galaxies were flying away — the universe was expanding.

If this is Einstein’s constant at work — and some astronomers despair of ever being able to say definitively whether it is or is not — the future is clear and dark. In their paper, Dr. Krauss and Dr. Scherrer extrapolated forward in time what has become a sort of standard model of the universe, 14 billion years old, and composed of a trace of ordinary matter, a lot of dark matter and Einstein’s cosmological constant.

As this universe expands and there is more space, there is more force pushing the galaxies outward faster and faster. As they approach the speed of light, the galaxies will approach a sort of horizon and simply vanish from view, as if they were falling into a black hole, their light shifted to infinitely long wavelengths and dimmed by their great speed. The most distant galaxies disappear first as the horizon slowly shrinks around us like a noose.

A similar cloak of invisibility will befall the afterglow of the Big Bang, an already faint bath of cosmic microwaves, whose wavelengths will be shifted so that they are buried by radio noise in our own galaxy. Another vital clue, the abundance of deuterium, a heavy form of hydrogen manufactured in the Big Bang, in deep space, will become unobservable because to be seen it needs to be backlit from distant quasars, and those quasars, of course, will have disappeared.

Eventually, in the far far future, this runaway dark energy will suck all the energy and life out of the universe. A few years ago, Edward Witten, a prominent theorist at the Institute for Advanced Study, called a universe that is accelerating forever “not very appealing.” Dr. Krauss has called it simply “the worst possible universe.”

But our future cosmologists will be spared this vision, according to the calculations. Instead they will puzzle about why the visible universe seems to consist of six galaxies, Dr. Krauss said. “What is the significance of six? Hundreds of papers will be written on that,” he said.

Those cosmologists may worry instead that their galaxy cloud will collapse into a black hole one day and, like Einstein, propose a cosmic repulsion to prevent it. But they will have no way of knowing if they were right.

Although by then the universe will be mostly dark energy, Dr. Krauss said, it will be undetectable unless astronomers want to follow the course of the occasional star that gets thrown out of the galaxy and is caught up in the dark cosmic current. But it would have to be followed for 10 billion years, he said — an experiment the National Science Foundation would be unlikely to finance.

“This is even weirder,” Dr. Krauss said. “Five billion years ago dark energy was unobservable; 100 billion years from now it will become invisible again.”

It turns out that you don’t actually need dark energy to be this pessimistic about the future, as Dr. Krauss and Dr. Scherrer point out. In 1987, George Ellis, a mathematician and astronomer at the University of Cape Town, in South Africa, and Tony Rothman, currently lecturing at Princeton, wrote a paper showing how even ordinary expansion would gradually carry most galaxies too far away to be seen, setting the stage for cosmic ignorance.

Dark energy speeds up the picture, Dr. Ellis said in an e-mail message, adding that he was glad to see the new paper, which adds many astrophysical details. “It’s an interesting gloss on the far future,” he said.

James Peebles, a Princeton cosmologist, said there were more pressing worries. We might be headed toward a universe that is “asymptotically empty,” he said, “But I have the uneasy feeling that the U.S.A. is headed into asymptotic futility well before that.”

You might object that the inhabitants of the far future will be far more advanced than we are. Maybe they will be able to detect dark energy — or the extra dimensions of string theory, for that matter — in the laboratory. Maybe they will even be us, in some form or other, if the human race manages to get out of the solar system before the Sun blows up in five billion years. But if relativity is right, they won’t be able to build telescopes that can see past the edge of the universe.

It’s not too late to start thinking about sending out the robot probes that could drift down through alien skies eons from now with, if not us or our DNA, at least a few nuggets of wisdom — that the world is made of atoms and that it started with a bang.

The lesson in the meantime is that we don’t know what we don’t know, and we never will — a lesson that extends beyond astronomy.

Einstein once said, “The Lord God is subtle but malicious he is not.”

I wondered in light of this new report whether it might be time to revise that quotation. Max Tegmark, a cosmologist at the Massachusetts Institute of Technology, told me the problem was not malice but human arrogance — a necessary but unfortunate condition for scientific progress.

“We have a tendency to put ourselves at the center of the universe,” he said. “We assume all we see is all there is.”

But, as Dr. Tegmark noted, Big Bang theorists already suppose that basic aspects of the universe are out of sight.

The reason we believe we live in a smooth, orderly universe instead of the chaotic one that is more likely, they say, is that the chaos has been hidden. According to the dominant theory of the Big Bang, known as inflation, an extremely violent version of dark energy blew it up a fraction of a second after time began, stretching and smoothing space and pushing all the wildness and chaos and even perhaps other universes out of the sky, where they will never be seen.

“Inflation tells us we live in a messy universe,” Dr. Tegmark said. Luckily we never have to confront it.

Ignorance is us, or is it bliss?

October 1, 1994

17 min read

The Evolution of the Universe

Some 15 billion years ago the universe emerged from a hot, dense sea of matter and energy. As the cosmos expanded and cooled, it spawned galaxies, stars, planets and life

By P. James E. Peebles , David N. Schramm , Edwin L. Turner & Richard G. Kron

GALAXY CLUSTER is representative of what the universe looked like when it was 60 percent of its present age. The Hubble Space Telescope captured the image by focusing on the cluster as it completed 10 orbits. This image is one of the longest and clearest exposures ever produced. Several pairs of galaxies appear to be caught in one another’s gravitational field. Such interactions are rarely found in nearby clusters and are evidence that the universe is evolving.

Editor’s Note (10/8/19): Cosmologist James Peebles won a 2019 Nobel Prize in Physics for his contributions to theories of how our universe began and evolved. He describes these ideas in this article, which he co-wrote for  Scientific American  in 1994.

At a particular instant roughly 15 billion years ago, all the matter and energy we can observe, concentrated in a region smaller than a dime, began to expand and cool at an incredibly rapid rate. By the time the temperature had dropped to 100 million times that of the sun’s core, the forces of nature assumed their present properties, and the elementary particles known as quarks roamed freely in a sea of energy. When the universe had expanded an additional 1,000 times, all the matter we can measure filled a region the size of the solar system.

At that time, the free quarks became confined in neutrons and protons. After the universe had grown by another factor of 1,000, protons and neutrons combined to form atomic nuclei, including most of the helium and deuterium present today. All of this occurred within the first minute of the expansion. Conditions were still too hot, however, for atomic nuclei to capture electrons. Neutral atoms appeared in abundance only after the expansion had continued for 300,000 years and the universe was 1,000 times smaller than it is now. The neutral atoms then began to coalesce into gas clouds, which later evolved into stars. By the time the universe had expanded to one fifth its present size, the stars had formed groups recognizable as young galaxies.

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When the universe was half its present size, nuclear reactions in stars had produced most of the heavy elements from which terrestrial planets were made. Our solar system is relatively young: it formed five billion years ago, when the universe was two thirds its present size. Over time the formation of stars has consumed the supply of gas in galaxies, and hence the population of stars is waning. Fifteen billion years from now stars like our sun will be relatively rare, making the universe a far less hospitable place for observers like us.

Our understanding of the genesis and evolution of the universe is one of the great achievements of 20th-century science. This knowledge comes from decades of innovative experiments and theories. Modern telescopes on the ground and in space detect the light from galaxies billions of light-years away, showing us what the universe looked like when it was young. Particle accelerators probe the basic physics of the high-energy environment of the early universe. Satellites detect the cosmic background radiation left over from the early stages of expansion, providing an image of the universe on the largest scales we can observe.

Our best efforts to explain this wealth of data are embodied in a theory known as the standard cosmological model or the big bang cosmology. The major claim of the theory is that in the largescale average the universe is expanding in a nearly homogeneous way from a dense early state. At present, there are no fundamental challenges to the big bang theory, although there are certainly unresolved issues within the theory itself. Astronomers are not sure, for example, how the galaxies were formed, but there is no reason to think the process did not occur within the framework of the big bang. Indeed, the predictions of the theory have survived all tests to date.

Yet the big bang model goes only so far, and many fundamental mysteries remain. What was the universe like before it was expanding? (No observation we have made allows us to look back beyond the moment at which the expansion began.) What will happen in the distant future, when the last of the stars exhaust the supply of nuclear fuel? No one knows the answers yet.

Our universe may be viewed in many lights—by mystics, theologians, philosophers or scientists. In science we adopt the plodding route: we accept only what is tested by experiment or observation. Albert Einstein gave us the now well-tested and accepted Theory of General Relativity, which establishes the relations between mass, energy, space and time. Einstein showed that a homogeneous distribution of matter in space fits nicely with his theory. He assumed without discussion that the universe is static, unchanging in the large-scale average [see “How Cosmology Became a Science,” by Stephen G. Brush; SCIENTIFIC AMERICAN, August 1992].

In 1922 the Russian theorist Alexander A. Friedmann realized that Einstein’s universe is unstable; the slightest perturbation would cause it to expand or contract. At that time, Vesto M. Slipher of Lowell Observatory was collecting the first evidence that galaxies are actually moving apart. Then, in 1929, the eminent astronomer Edwin P. Hubble showed that the rate a galaxy is moving away from us is roughly proportional to its distance from us.

MULTIPLE IMAGES of a distant quasar ( left ) are the result of an effect known as gravitational lensing. The effect occurs when light from a distant object is bent by the gravitational field of an intervening galaxy. In this case, the galaxy, which is visible in the center, produces four images of the quasar. The photograph was produced using the Hubble telescope.

The existence of an expanding universe implies that the cosmos has evolved from a dense concentration of matter into the present broadly spread distribution of galaxies. Fred Hoyle, an English cosmologist, was the first to call this process the big bang. Hoyle intended to disparage the theory, but the name was so catchy it gained popularity. It is somewhat misleading, however, to describe the expansion as some type of explosion of matter away from some particular point in space.

That is not the picture at all: in Einstein’s universe the concept of space and the distribution of matter are intimately linked; the observed expansion of the system of galaxies reveals the unfolding of space itself. An essential feature of the theory is that the average density in space declines as the universe expands; the distribution of matter forms no observable edge. In an explosion the fastest particles move out into empty space, but in the big bang cosmology, particles uniformly fill all space. The expansion of the universe has had little influence on the size of galaxies or even clusters of galaxies that are bound by gravity; space is simply opening up between them. In this sense, the expansion is similar to a rising loaf of raisin bread. The dough is analogous to space, and the raisins, to clusters of galaxies. As the dough expands, the raisins move apart. Moreover, the speed with which any two raisins move apart is directly and positively related to the amount of dough separating them.

The evidence for the expansion of the universe has been accumulating for some 60 years. The first important clue is the redshift. A galaxy emits or absorbs some wavelengths of light more strongly than others. If the galaxy is moving away from us, these emission and absorption features are shifted to longer wavelengths—that is, they become redder as the recession velocity increases. This phenomenon is known as the redshift.

Hubble’s measurements indicated that the redshift of a distant galaxy is greater than that of one closer to the earth. This relation, now known as Hubble’s law, is just what one would expect in a uniformly expanding universe. Hubble’s law says the recession velocity of a galaxy is equal to its distance multiplied by a quantity called Hubble’s constant. The redshift effect in nearby galaxies is relatively subtle, requiring good instrumentation to detect it. In contrast, the redshift of very distant objects—radio galaxies and quasars—is an awesome phenomenon; some appear to be moving away at greater than 90 percent of the speed of light.

Hubble contributed to another crucial part of the picture. He counted the number of visible galaxies in different directions in the sky and found that they appear to be rather uniformly distributed. The value of Hubble’s constant seemed to be the same in all directions, a necessary consequence of uniform expansion. Modern surveys confirm the fundamental tenet that the universe is homogeneous on large scales. Although maps of the distribution of the nearby galaxies display clumpiness, deeper surveys reveal considerable uniformity.

The Milky Way, for instance, resides in a knot of two dozen galaxies; these in turn are part of a complex of galaxies that protrudes from the so-called local supercluster. The hierarchy of clustering has been traced up to dimensions of about 500 million light-years. The fluctuations in the average density of matter diminish as the scale of the structure being investigated increases. In maps that cover distances that reach close to the observable limit, the average density of matter changes by less than a tenth of a percent.

To test Hubble’s law, astronomers need to measure distances to galaxies. One method for gauging distance is to observe the apparent brightness of a galaxy. If one galaxy is four times fainter in the night sky than an otherwise comparable galaxy, then it can be estimated to be twice as far away. This expectation has now been tested over the whole of the visible range of distances.

HOMOGENEOUS DISTRIBUTION of galaxies is apparent in a map that includes objects from 300 to 1,000 million light-years away. The only inhomogeneity, a gap near the center line, occurs because part of the sky is obscured by the Milky Way. Michael Strauss of the Institute for Advanced Study in Princeton, N.J., created the map using data from NASA’s Infrared Astronomical Satellite .

Some critics of the theory have pointed out that a galaxy that appears to be smaller and fainter might not actually be more distant. Fortunately, there is a direct indication that objects whose redshifts are larger really are more distant. The evidence comes from observations of an effect known as gravitational lensing. An object as massive and compact as a galaxy can act as a crude lens, producing a distorted, magnified image (or even many images) of any background radiation source that lies behind it. Such an object does so by bending the paths of light rays and other electromagnetic radiation. So if a galaxy sits in the line of sight between the earth and some distant object, it will bend the light rays from the object so that they are observable [see “Gravitational Lenses,” by Edwin L. Turner; SCIENTIFIC AMERICAN, July 1988]. During the past decade, astronomers have discovered more than a dozen gravitational lenses. The object behind the lens is always found to have a higher redshift than the lens itself, confirming the qualitative prediction of Hubble’s law.

Hubble’s law has great significance not only because it describes the expansion of the universe but also because it can be used to calculate the age of the cosmos. To be precise, the time elapsed since the big bang is a function of the present value of Hubble’s constant and its rate of change. Astronomers have determined the approximate rate of the expansion, but no one has yet been able to measure the second value precisely.

Still, one can estimate this quantity from knowledge of the universe’s average density. One expects that because gravity exerts a force that opposes expansion, galaxies would tend to move apart more slowly now than they did in the past. The rate of change in expansion is therefore related to the gravitational pull of the universe set by its average density. If the density is that of just the visible material in and around galaxies, the age of the universe probably lies between 12 and 20 billion years. (The range allows for the uncertainty in the rate of expansion.)

Yet many researchers believe the density is greater than this minimum value. So-called dark matter would make up the difference. A strongly defended argument holds that the universe is just dense enough that in the remote future the expansion will slow almost to zero. Under this assumption, the age of the universe decreases to the range of seven to 13 billion years.

DENSITY of neutrons and protons in the universe determined the abundances of certain elements. For a higher density universe, the computed helium abundance is little different, and the computed abundance of deuterium is considerably lower. The shaded region is consistent with the observations, ranging from an abundance of 24 percent for helium to one part in 1010 for the lithium isotope. This quantitative agreement is a prime success of the big bang cosmology.

To improve these estimates, many astronomers are involved in intensive research to measure both the distances to galaxies and the density of the universe. Estimates of the expansion time provide an important test for the big bang model of the universe. If the theory is correct, everything in the visible universe should be younger than the expansion time computed from Hubble’s law.

These two timescales do appear to be in at least rough concordance. For example, the oldest stars in the disk of the Milky Way galaxy are about nine billion years old—an estimate derived from the rate of cooling of white dwarf stars. The stars in the halo of the Milky Way are somewhat older, about 15 billion years—a value derived from the rate of nuclear fuel consumption in the cores of these stars. The ages of the oldest known chemical elements are also approximately 15 billion years—a number that comes from radioactive dating techniques. Workers in laboratories have derived these age estimates from atomic and nuclear physics. It is noteworthy that their results agree, at least approximately, with the age that astronomers have derived by measuring cosmic expansion.

Another theory, the steady state theory, also succeeds in accounting for the expansion and homogeneity of the universe. In 1946 three physicists in England—Hoyle, Hermann Bondi and Thomas Gold—proposed such a cosmology. In their theory the universe is forever expanding, and matter is created spontaneously to fill the voids. As this material accumulates, they suggested, it forms new stars to replace the old. This steady state hypothesis predicts that ensembles of galaxies close to us should look statistically the same as those far away. The big bang cosmology makes a different prediction: if galaxies were all formed long ago, distant galaxies should look younger than those nearby because light from them requires a longer time to reach us. Such galaxies should contain more shortlived stars and more gas out of which future generations of stars will form.

The test is simple conceptually, but it took decades for astronomers to develop detectors sensitive enough to study distant galaxies in detail. When astronomers examine nearby galaxies that are powerful emitters of radio wavelengths, they see, at optical wavelengths, relatively round systems of stars. Distant radio galaxies, on the other hand, appear to have elongated and sometimes irregular structures. Moreover, in most distant radio galaxies, unlike the ones nearby, the distribution of light tends to be aligned with the pattern of the radio emission.

Likewise, when astronomers study the population of massive, dense clusters of galaxies, they find differences between those that are close and those far away. Distant clusters contain bluish galaxies that show evidence of ongoing star formation. Similar clusters that are nearby contain reddish galaxies in which active star formation ceased long ago. Observations made with the Hubble Space Telescope confirm that at least some of the enhanced star formation in these younger clusters may be the result of collisions between their member galaxies, a process that is much rarer in the present epoch.

DISTANT GALAXIES differ greatly from those nearby—an observation that shows that galaxies evolved from earlier, more irregular forms. Among galaxies that are bright at both optical ( blue ) and radio ( red ) wavelengths, the nearby galaxies tend to have smooth elliptical shapes at optical wavelengths and very elongated radio images. As redshift, and therefore distance, increases, galaxies have more irregular elongated forms that appear aligned at optical and radio wavelengths. The galaxy at the far right is seen as it was at 10 percent of the present age of the universe. The images were assembled by Pat McCarthy of the Carnegie Institute.

So if galaxies are all moving away from one another and are evolving from earlier forms, it seems logical that they were once crowded together in some dense sea of matter and energy. Indeed, in 1927, before much was known about distant galaxies, a Belgian cosmologist and priest, Georges Lemaître, proposed that the expansion of the universe might be traced to an exceedingly dense state he called the primeval “super-atom.” It might even be possible, he thought, to detect remnant radiation from the primeval atom. But what would this radiation signature look like?

When the universe was very young and hot, radiation could not travel very far without being absorbed and emitted by some particle. This continuous exchange of energy maintained a state of thermal equilibrium; any particular region was unlikely to be much hotter or cooler than the average. When matter and energy settle to such a state, the result is a so-called thermal spectrum, where the intensity of radiation at each wavelength is a definite function of the temperature. Hence, radiation originating in the hot big bang is recognizable by its spectrum.

In fact, this thermal cosmic background radiation has been detected. While working on the development of radar in the 1940s, Robert H. Dicke, then at the Massachusetts Institute of Technology, invented the microwave radiometer—a device capable of detecting low levels of radiation. In the 1960s Bell Laboratories used a radiometer in a telescope that would track the early communications satellites Echo-1 and Telstar. The engineer who built this instrument found that it was detecting unexpected radiation. Arno A. Penzias and Robert W. Wilson identified the signal as the cosmic background radiation. It is interesting that Penzias and Wilson were led to this idea by the news that Dicke had suggested that one ought to use a radiometer to search for the cosmic background.

Astronomers have studied this radiation in great detail using the Cosmic Background Explorer (COBE) satellite and a number of rocket-launched, balloon-borne and ground-based experiments. The cosmic background radiation has two distinctive properties. First, it is nearly the same in all directions. (As George F. Smoot of Lawrence Berkeley Laboratory and his team discovered in 1992, the variation is just one part per 100,000.) The interpretation is that the radiation uniformly fills space, as predicted in the big bang cosmology. Second, the spectrum is very close to that of an object in thermal equilibrium at 2.726 kelvins above absolute zero. To be sure, the cosmic background radiation was produced when the universe was far hotter than 2.726 degrees, yet researchers anticipated correctly that the apparent temperature of the radiation would be low. In the 1930s Richard C. Tolman of the California Institute of Technology showed that the temperature of the cosmic background would diminish because of the universe’s expansion.

The cosmic background radiation provides direct evidence that the universe did expand from a dense, hot state, for this is the condition needed to produce the radiation. In the dense, hot early universe thermonuclear reactions produced elements heavier than hydrogen, including deuterium, helium and lithium. It is striking that the computed mix of the light elements agrees with the observed abundances. That is, all evidence indicates that the light elements were produced in the hot, young universe, whereas the heavier elements appeared later, as products of the thermonuclear reactions that power stars.

The theory for the origin of the light elements emerged from the burst of research that followed the end of World War II. George Gamow and graduate student Ralph A. Alpher of George Washington University and Robert Herman of the Johns Hopkins University Applied Physics Laboratory and others used nuclear physics data from the war e›ort to predict what kind of nuclear processes might have occurred in the early universe and what elements might have been produced. Alpher and Herman also realized that a remnant of the original expansion would still be detectable in the existing universe.

Despite the fact that significant details of this pioneering work were in error, it forged a link between nuclear physics and cosmology. The workers demonstrated that the early universe could be viewed as a type of thermonuclear reactor. As a result, physicists have now precisely calculated the abundances of light elements produced in the big bang and how those quantities have changed because of subsequent events in the interstellar medium and nuclear processes in stars.

Our grasp of the conditions that prevailed in the early universe does not translate into a full understanding of how galaxies formed. Nevertheless, we do have quite a few pieces of the puzzle. Gravity causes the growth of density fluctuations in the distribution of matter, because it more strongly slows the expansion of denser regions, making them grow still denser. This process is observed in the growth of nearby clusters of galaxies, and the galaxies themselves were probably assembled by the same process on a smaller scale.

The growth of structure in the early universe was prevented by radiation pressure, but that changed when the universe had expanded to about 0.1 percent of its present size. At that point, the temperature was about 3,000 kelvins, cool enough to allow the ions and electrons to combine to form neutral hydrogen and helium. The neutral matter was able to slip through the radiation and to form gas clouds that could collapse to star clusters. Observations show that by the time the universe was one fifth its present size, matter had gathered into gas clouds large enough to be called young galaxies.

A pressing challenge now is to reconcile the apparent uniformity of the early universe with the lumpy distribution of galaxies in the present universe. Astronomers know that the density of the early universe did not vary by much, because they observe only slight irregularities in the cosmic background radiation. So far it has been easy to develop theories that are consistent with the available measurements, but more critical tests are in progress. In particular, different theories for galaxy formation predict quite different fluctuations in the cosmic background radiation on angular scales less than about one degree. Measurements of such tiny fluctuations have not yet been done, but they might be accomplished in the generation of experiments now under way. It will be exciting to learn whether any of the theories of galaxy formation now under consideration survive these tests.

The present-day universe has provided ample opportunity for the development of life as we know it—there are some 100 billion billion stars similar to the sun in the part of the universe we can observe. The big bang cosmology implies, however, that life is possible only for a bounded span of time: the universe was too hot in the distant past, and it has limited resources for the future. Most galaxies are still producing new stars, but many others have already exhausted their supply of gas. Thirty billion years from now, galaxies will be much darker and filled with dead or dying stars, so there will be far fewer planets capable of supporting life as it now exists.

The universe may expand forever, in which case all the galaxies and stars will eventually grow dark and cold. The alternative to this big chill is a big crunch. If the mass of the universe is large enough, gravity will eventually reverse the expansion, and all matter and energy will be reunited. During the next decade, as researchers improve techniques for measuring the mass of the universe, we may learn whether the present expansion is headed toward a big chill or a big crunch.

In the near future, we expect new experiments to provide a better understanding of the big bang. As we improve measurements of the expansion rate and the ages of stars, we may be able to confirm that the stars are indeed younger than the expanding universe. The larger telescopes recently completed or under construction may allow us to see how the mass of the universe affects the curvature of spacetime, which in turn influences our observations of distant galaxies.

We will also continue to study issues that the big bang cosmology does not address. We do not know why there was a big bang or what may have existed before. We do not know whether our universe has siblings—other expanding regions well removed from what we can observe. We do not understand why the fundamental constants of nature have the values they do. Advances in particle physics suggest some interesting ways these questions might be answered; the challenge is to find experimental tests of the ideas.

In following the debate on such matters of cosmology, one should bear in mind that all physical theories are approximations of reality that can fail if pushed too far. Physical science advances by incorporating earlier theories that are experimentally supported into larger, more encompassing frameworks. The big bang theory is supported by a wealth of evidence: it explains the cosmic background radiation, the abundances of light elements and the Hubble expansion. Thus, any new cosmology surely will include the big bang picture. Whatever developments the coming decades may bring, cosmology has moved from a branch of philosophy to a physical science where hypotheses meet the test of observation and experiment.

How the Universe Works Essay

• To find inspiration for your paper and overcome writer’s block
• As a source of information (ensure proper referencing)
• As a template for you assignment

For us, the Universe we live in is absolute and unlimited. We think it existed, exists and will always exist, although something inside us has never ceased to claim that everything has a beginning. There are a lot of the Universe origin theories, and the most famous one is probably the Big Bang Theory, according to which there was a great explosion of dense matter and energy 13 billion years ago, which resulted in what we nowadays call the Universe. Many scientists also believe that the Big Bang was just a cycle in an endless series of matter explosions, which has neither a beginning nor an end. Points of view differ, and the dispute lasts for centuries because of the attempts to understand and organize the stardate back to ancient times.

Over time the Universe was divided into galaxies, which nowadays are numbered in millions. More and more of them are being opened, so even the scientists cannot tell the exact number of the existing ones, although they managed to classify them into three main types: Spiral, Elliptical and Irregular. But whatever the type of Galaxy is, each one is composed of numerous stars, planets, asteroids, meteoroids intergalactic gas and black matter.

The Galaxy we have the pleasure to live in is called The Milky Way and refers to a type of spiral galaxy. It has a form of a flat disc with a large bulge in the middle. The Earth used to be considered the centre of our Galaxy for a very long time. After this the scientists made a mistaken assumption, stating that the centre of the Milky Way Galaxy was the Sun. In fact, the “heart” of the Galaxy located in its middle is a supermassive black hole, which is overwhelming in its size being three million times larger than the Sun.

These data have recently been obtained as a result of a constant 15-year long space study by scientists of the Galactic Centre and its ESO telescopes at the La Silla Paranal Observatory. The black hole situated in The Milky way does not come close to other cosmic bodies and has unique abilities to convert matter into energy and extrude material at a speed close to the speed of light. By far there have not been detected any objects in the entire universe with such incredible properties.

The place occupied by our Sun among the stars in the Galaxy is fairly modest: it is an average one among billions of ordinary stars and it is twice farther from the centre of the Galaxy than from its edge. However, for us, the Sun will always remain the most beautiful and important star, the only one in its system, which served as a name for the whole system. The Solar System consists of eight planets, each located on its own distances, and the farther the planet from the Sun is, the longer its orbit is. Each planet has its own natural satellites, and there may be either one of them, as in the Earth’s case, for example, or ten and more, as some giant planets have. There are two exceptions to this system though – Mercury and Venus have no moons.

Our Sun is very bright and glittering, and its surface recalls a boiling gas mixture with a temperature of about 9941 °F. It consists of 74% of hydrogen, 24% of helium and the remaining 2% include a small amount of iron and nickel. In other words, the entire Solar System is composed mostly of hydrogen. Its structure, of course, includes other substances, but their percentage is only 0.1%. The Sun is heavier than all the planets, so it has a huge gravitational force that keeps the planets in their orbits.

The Earth is the third planet in The Solar System and is about 150 million miles away, while the light emitted by the Sun is still able to cover this distance in just eight minutes. The Sun mass is bigger than the Earth’s approximately 330 thousand times and larger in 109 times.

Although these numbers may seem huge to us, there exist much bigger stars than the Sun, such as Sirius, Betelgeuse and Antares, though they are incredibly far away. But their size and brightness give us a chance to distinguish them in the night sky, among other 6000 stars visible to the naked man’s eye on a clear night sky.

Size is not the only difference stars have in common. Colour is another category that varies depending on the temperature and can fluctuate from red to white or blue. The coolest stars are represented by the red colour, while the blue one is an indication of the hottest stars, which surface temperatures can rise above 12000° F.

There are also many similarities between the stars. They are all born from a cloud of cold molecular hydrogen, which is gravitationally compressed at its first stage. When the cloud is fragmented, many of its parts are generated in separate stars. Material is shaped in the form close to a ball and constantly undergoes the influence of its own gravity. Meanwhile, the temperature in its centre goes higher and higher until it runs up to the level necessary to ignite nuclear fusion.

If one bothered to collect all stars together and compare their size and structure in order to find out which ones are the most popular, the biggest group would definitely consist of red dwarfs. They have less than 50% of the mass of the Sun and can weigh even 7.5 per cent less.

Death is another common event in stars’ lives. They pass away gradually (billions of years) because of the failure of nuclear fuel. Hydrogen is converted to helium, which is concentrated in the nucleus, and helium reactions occur only on the surface of the star. The core of the star begins to cool and the stars collapse inside. Unfortunately, according to scientists, our Sun will also burn out completely in 6 billion years.

All these facts and other data about the stars and space are available to us mostly thanks to telescopes. Today, there are seven complexes that have telescopes with a mirror diameter of more than eight meters. The largest of them is located in the Atacama Large Millimeter Research Center Array in Chile. The biggest telescope in the world is made up of 66 radio telescopes with diameters from seven to twelve meters. They are all combined into a single device that has an incredible resolution and can capture objects in the depths of the early Universe, where the galaxies were formed billions of years ago.

In the nearest future, we expect to see the construction and introduction of telescope tools with a primary mirror diameter of 30 and 39 meters. So, the biggest star records are still to be set. Who knows what other secrets our Universe will tell us and whether all her secrets can be revealed at all. On the other hand, the most important thing is what we want to know and what we actually need: to disclose all mysteries, classify all-stars, systems and galaxies and mark the accurate space borders or fascinate the very process of finding out new information about how our Universe works.

• Origin of the Universe
• Ancient Warming in Antarctica: Astronomical Discovery
• Telescope's Part in Astronomy
• The Milky Way and the Expanding Universe
• The Origin of Galaxies: Theories Explaining
• Liquid Lake on Mars
• The Gregorian Calendar and the Egyptian Calendar
• Humanities: Galileo and Four Moons of Jupiter
• Solar Calendar and Its Different Types
• How Close Is the Success of Suborbital Commercial Space Shuttles?
• Chicago (A-D)
• Chicago (N-B)

IvyPanda. (2022, January 29). How the Universe Works. https://ivypanda.com/essays/how-the-universe-works/

"How the Universe Works." IvyPanda , 29 Jan. 2022, ivypanda.com/essays/how-the-universe-works/.

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IvyPanda . 2022. "How the Universe Works." January 29, 2022. https://ivypanda.com/essays/how-the-universe-works/.

1. IvyPanda . "How the Universe Works." January 29, 2022. https://ivypanda.com/essays/how-the-universe-works/.

Bibliography

IvyPanda . "How the Universe Works." January 29, 2022. https://ivypanda.com/essays/how-the-universe-works/.

How did the universe begin—and what were its early days like?

The most popular theory of our universe's origin centers on a cosmic cataclysm unmatched in all of history—the big bang.

The best-supported theory of our universe's origin centers on an event known as the big bang. This theory was born of the observation that other galaxies are moving away from our own at great speed in all directions, as if they had all been propelled by an ancient explosive force.

A Belgian priest named Georges Lemaître first suggested the big bang theory in the 1920s, when he theorized that the universe began from a single primordial atom. The idea received major boosts from Edwin Hubble's observations that galaxies are speeding away from us in all directions, as well as from the 1960s discovery of cosmic microwave radiation—interpreted as echoes of the big bang—by Arno Penzias and Robert Wilson.

Further work has helped clarify the big bang's tempo. Here’s the theory: In the first 10^-43 seconds of its existence, the universe was very compact, less than a million billion billionth the size of a single atom. It's thought that at such an incomprehensibly dense, energetic state, the four fundamental forces—gravity, electromagnetism, and the strong and weak nuclear forces—were forged into a single force, but our current theories haven't yet figured out how a single, unified force would work. To pull this off, we'd need to know how gravity works on the subatomic scale, but we currently don't.

It's also thought that the extremely close quarters allowed the universe's very first particles to mix, mingle, and settle into roughly the same temperature. Then, in an unimaginably small fraction of a second, all that matter and energy expanded outward more or less evenly, with tiny variations provided by fluctuations on the quantum scale. That model of breakneck expansion, called inflation, may explain why the universe has such an even temperature and distribution of matter.

After inflation, the universe continued to expand but at a much slower rate. It's still unclear what exactly powered inflation.

Aftermath of cosmic inflation

As time passed and matter cooled, more diverse kinds of particles began to form, and they eventually condensed into the stars and galaxies of our present universe.

By the time the universe was a billionth of a second old, the universe had cooled down enough for the four fundamental forces to separate from one another. The universe's fundamental particles also formed. It was still so hot, though, that these particles hadn't yet assembled into many of the subatomic particles we have today, such as the proton. As the universe kept expanding, this piping-hot primordial soup—called the quark-gluon plasma—continued to cool. Some particle colliders, such as CERN's Large Hadron Collider , are powerful enough to re-create the quark-gluon plasma.

Radiation in the early universe was so intense that colliding photons could form pairs of particles made of matter and antimatter, which is like regular matter in every way except with the opposite electrical charge. It's thought that the early universe contained equal amounts of matter and antimatter. But as the universe cooled, photons no longer packed enough punch to make matter-antimatter pairs. So like an extreme game of musical chairs, many particles of matter and antimatter paired off and annihilated one another.

Somehow, some excess matter survived—and it's now the stuff that people, planets, and galaxies are made of. Our existence is a clear sign that the laws of nature treat matter and antimatter slightly differently. Researchers have experimentally observed this rule imbalance, called CP violation , in action. Physicists are still trying to figure out exactly how matter won out in the early universe.

A tiny, ghostly particle called a neutrino and its antimatter counterpart, an antineutrino, could shed some light on the matter, and two big experiments, called DUNE and Hyper-Kamiokande , are using these chargeless, nearly massless particles to try to solve the mystery.

Building atoms

Within the universe's first second, it was cool enough for the remaining matter to coalesce into protons and neutrons, the familiar particles that make up atoms' nuclei. And after the first three minutes, the protons and neutrons had assembled into hydrogen and helium nuclei. By mass, hydrogen was 75 percent of the early universe's matter, and helium was 25 percent. The abundance of helium is a key prediction of big bang theory, and it's been confirmed by scientific observations.

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Despite having atomic nuclei, the young universe was still too hot for electrons to settle in around them to form stable atoms. The universe's matter remained an electrically charged fog that was so dense, light had a hard time bouncing its way through. It would take another 380,000 years or so for the universe to cool down enough for neutral atoms to form—a pivotal moment called recombination. The cooler universe made it transparent for the first time, which let the photons rattling around within it finally zip through unimpeded.

We still see this primordial afterglow today as cosmic microwave background radiation , which is found throughout the universe. The radiation is similar to that used to transmit TV signals via antennae. But it is the oldest radiation known and may hold many secrets about the universe's earliest moments.

From the first stars to today

There wasn't a single star in the universe until about 180 million years after the big bang. It took that long for gravity to gather clouds of hydrogen and forge them into stars. Many physicists think that vast clouds of dark matter , a still-unknown material that outweighs visible matter by more than five to one, provided a gravitational scaffold for the first galaxies and stars.

Once the universe's first stars ignited , the light they unleashed packed enough punch to once again strip electrons from neutral atoms, a key chapter of the universe called reionization. Scientists have tried to glimpse this “cosmic dawn,” but the results have been mixed. Back in 2018, an Australian team announced detected signs of the first stars forming around 180 million years after the big bang, though other groups haven't been able to recreate their results. By 300 million years after the big bang , the first galaxies were born. In the billions of years since, stars, galaxies, and clusters of galaxies have formed and re-formed—eventually yielding our home galaxy, the Milky Way, and our cosmic home, the solar system.

Even now the universe is expanding . To astronomers' surprise, the pace of expansion is accelerating . Estimates of the expansion rate vary, but data from the James Webb Space Telescope adds to a growing body of evidence that it's significantly faster than it should be.

It's thought that this acceleration is driven by a force that repels gravity called dark energy. We still don't know what dark energy is, but it’s thought that it makes up 68 percent of the universe's total matter and energy. Dark matter makes up another 27 percent. In essence, all the matter you've ever seen—from your first love to the stars overhead—makes up less than five percent of the universe.

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Essay on Our Universe

Students are often asked to write an essay on Our Universe in their schools and colleges. And if you’re also looking for the same, we have created 100-word, 250-word, and 500-word essays on the topic.

Let’s take a look…

100 Words Essay on Our Universe

What is the universe.

The universe is a vast space that holds everything we know – from tiny atoms to giant galaxies. It includes all of space, time, energy, and matter. Imagine it as a huge home where all the stars, planets, and moons live. It’s so big that we can’t see the end of it, and it’s always expanding.

Stars and Galaxies

Stars are like giant balls of gas that give off light and heat. They group together to form galaxies. Our sun is a star, and it’s part of a galaxy we call the Milky Way. There are billions of galaxies each with its own stars.

Planets and Moons

Planets are big objects that orbit, or go around, a star. Earth is a planet that goes around our sun. Some planets have moons, which are smaller objects that orbit planets. Just like Earth has one moon, other planets can have many.

The Mystery of Space

Space is full of mysteries. Scientists use telescopes to study far-away stars and planets. They’re trying to learn more about black holes, which are places in space where gravity is very strong, and about the possibility of life beyond Earth.

250 Words Essay on Our Universe

The big bang.

The universe began with a huge explosion called the Big Bang about 13.8 billion years ago. This explosion made all the space, time, matter, and energy in the universe. It started very small and hot, then cooled and stretched to become as big as it is now, and it’s still expanding.

Stars are huge balls of hot gas that give off light and heat. Our sun is a star. There are billions of stars in the universe. Stars group together to form galaxies. Our galaxy is called the Milky Way, and it has billions of stars too. There are so many galaxies we can’t count them all.

Planets are big objects that orbit, or go around, stars. Our Earth is a planet. Some planets have moons that orbit them. Moons are smaller than planets and there are hundreds of moons in our universe.

Exploring the Universe

Scientists use telescopes to look at stars, planets, and galaxies. They use space probes to explore things too far to see with telescopes. By studying the universe, we learn more about where we come from and our place in the cosmos.

500 Words Essay on Our Universe

Introduction to the universe.

The universe is like a huge home with many rooms, each filled with stars, planets, and all sorts of interesting things. Imagine looking up at the night sky. Every star you see is part of our universe. It is everything that exists, from the smallest ant to the biggest galaxy.

What’s in the Universe?

The size of our universe.

Think of the biggest thing you’ve ever seen. Now imagine something a million times bigger. Our universe is even larger than that! It’s so big that we measure how far things are in it with a special word: “light-year.” A light-year is the distance light travels in one year, and light is super fast!

The Beginning of Everything

A long time ago, scientists believe the universe started with a big bang. It wasn’t an explosion, but more like everything, all the space, time, and stuff that would become galaxies, started expanding from a tiny point. Since then, the universe has been getting bigger and bigger.

The Life of Stars

Humans have always been curious about the stars. We’ve used telescopes to look far away, and we’ve sent spacecraft to explore planets and moons. Some spacecraft, like the Voyager probes, have even left our solar system and are sending back information from beyond.

The Mystery of Dark Matter and Dark Energy

There are things in the universe we can’t see called dark matter and dark energy. We know they’re there because they affect how galaxies move and how the universe is growing. But what they are exactly is still a big question.

Our Place in the Universe

Our universe is a fascinating and mysterious place. It’s full of wonders that we are just beginning to understand. As we continue to look up at the stars and learn more, we realize how amazing it is that we are a part of something so vast and incredible. The universe is the biggest adventure waiting for us to explore.

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1.9 A Conclusion and a Beginning

If you are new to astronomy, you have probably reached the end of our brief tour in this chapter with mixed emotions. On the one hand, you may be fascinated by some of the new ideas you’ve read about and you may be eager to learn more. On the other hand, you may be feeling a bit overwhelmed by the number of topics we have covered, and the number of new words and ideas we have introduced. Learning astronomy is a little like learning a new language: at first it seems there are so many new expressions that you’ll never master them all, but with practice, you soon develop facility with them.

At this point you may also feel a bit small and insignificant, dwarfed by the cosmic scales of distance and time. But, there is another way to look at what you have learned from our first glimpses of the cosmos. Let us consider the history of the universe from the Big Bang to today and compress it, for easy reference, into a single year. (We have borrowed this idea from Carl Sagan’s 1977 Pulitzer Prize-winning book, The Dragons of Eden .)

On this scale, the Big Bang happened at the first moment of January 1, and this moment, when you are reading this chapter would be the end of the very last second of December 31. When did other events in the development of the universe happen in this “cosmic year?” Our solar system formed around September 10, and the oldest rocks we can date on Earth go back to the third week in September ( Figure 1.15 ).

Where does the origin of human beings fall during the course of this cosmic year? The answer turns out to be the evening of December 31. The invention of the alphabet doesn’t occur until the fiftieth second of 11:59 p.m. on December 31. And the beginnings of modern astronomy are a mere fraction of a second before the New Year. Seen in a cosmic context, the amount of time we have had to study the stars is minute, and our success in piecing together as much of the story as we have is remarkable.

Certainly our attempts to understand the universe are not complete. As new technologies and new ideas allow us to gather more and better data about the cosmos, our present picture of astronomy will very likely undergo many changes. Still, as you read our current progress report on the exploration of the universe, take a few minutes every once in a while just to savor how much you have already learned.

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Home — Essay Samples — Science — Universe — The Beginning of the Universe

The Beginning of The Universe

• Categories: Creation Myth Universe

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Words: 1323 |

Published: Nov 16, 2018

Words: 1323 | Pages: 3 | 7 min read

Works Cited

• Greene, B. (2004). The Fabric of the Cosmos: Space, Time, and the Texture of Reality. Knopf.
• Guth, A. H. (1997). The Inflationary Universe: The Quest for a New Theory of Cosmic Origins. Perseus Books.
• Hawking, S. (1988). A Brief History of Time: From the Big Bang to Black Holes. Bantam Books.
• Krauss, L. M. (2012). A Universe from Nothing: Why There Is Something Rather Than Nothing. Free Press.
• Lemaître, G. (1931). The Primeval Atom Hypothesis and the Problem of Clusters of Galaxies. Monthly Notices of the Royal Astronomical Society, 91(5), 483-490.
• Linde, A. (1990). Particle Physics and Inflationary Cosmology. Contemporary Concepts in Physics, 5, 295-339.
• Peebles, P. J. E. (1993). Principles of Physical Cosmology. Princeton University Press.
• Penrose, R. (2004). The Road to Reality: A Complete Guide to the Laws of the Universe. Vintage Books.
• Rees, M. J. (2000). Just Six Numbers: The Deep Forces That Shape the Universe. Basic Books.
• Weinberg, S. (1972). Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity. John Wiley & Sons.

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• The Universe

The Universe is everything we can touch, feel, sense, measure or detect. It includes living things, planets, stars, galaxies, dust clouds, light, and even time. Before the birth of the Universe, time, space and matter did not exist.

The Universe contains billions of galaxies, each containing millions or billions of stars. The space between the stars and galaxies is largely empty. However, even places far from stars and planets contain scattered particles of dust or a few hydrogen atoms per cubic centimeter. Space is also filled with radiation (e.g. light and heat), magnetic fields and high energy particles (e.g. cosmic rays).

The Universe is incredibly huge. It would take a modern jet fighter more than a million years to reach the nearest star to the Sun. Travelling at the speed of light (300,000 km per second), it would take 100,000 years to cross our Milky Way galaxy alone.

No one knows the exact size of the Universe, because we cannot see the edge – if there is one. All we do know is that the visible Universe is at least 93 billion light years across. (A light year is the distance light travels in one year – about 9 trillion km.)

The Universe has not always been the same size. Scientists believe it began in a Big Bang, which took place nearly 14 billion years ago. Since then, the Universe has been expanding outward at very high speed. So the area of space we now see is billions of times bigger than it was when the Universe was very young. The galaxies are also moving further apart as the space between them expands.

Story of the Universe

• Extreme life
• In the beginning
• The Big Bang
• The birth of galaxies
• What is space?
• Black Holes
• The mystery of the dark Universe
• Cosmic distances

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Essay on our universe: definition, stars and solar system.

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Essay  on Our Universe: Definition, Stars and Solar System!

When we look at the sky, we see different kinds of natural bodies like the sun, the stars, the moon, and so on. The natural bodies in the sky are called celestial bodies or heavenly bodies. They are part of our universe. The universe is a huge space which contains everything that exists. The celestial bodies that we see are just a small fraction of the bodies that exist in the universe. One of the reasons why we do not see more of them is that they are very, very far away.

To measure the large distances in the universe, scientists use a unit of length called the light year. A light year is the distance travelled by light in one year. Light travels 9.46 trillion km in a year (one trillion is 1 followed by 12 zeroes).

One light year represents this huge distance. Proxima Centauri, the star closest to our solar system, is 4.2 light years from us. This means that light from this star takes 4.2 years to reach us. In this article, we shall learn a bit about stars and our solar system. But before that, let us see how the universe was formed.

Scientists believe that the universe was born after a massive explosion called the ‘big bang’. A long time after the big bang, stars like our sun were formed. At that time, clouds of hot gases and particles revolved around the sun. Over time, many particles got stuck together to form large bodies. These bodies pulled in smaller objects near them by gravitational force. This made them larger still. These bodies finally became the planets.

Away from the lights of the city, you can see thousands of stars in the night sky. You can also see some planets and their moons, either with the naked eye or with the help of a telescope. These celestial bodies are different from the stars in one important way. Stars are celestial bodies that produce their own heat and light. Planets and their moons shine by reflecting the light of a star such as our sun.

All stars are huge balls of hydrogen and helium gases. In a star, hydrogen gets converted into helium. In this reaction, a large amount of energy is liberated. This is the source of the heat and light of a star. Stars vary in brightness and size. Some are medium-sized, like our sun. Some are so huge that if they were to be placed in our sun’s position, they would fill the entire solar system!

There are trillions of stars in the universe. They occur in groups called galaxies. The gravitational force between stars keeps the stars of a galaxy together. Apart from stars, a galaxy may have other celestial bodies like planets and moons. So you can say that a galaxy is a group of stars and other celestial bodies bound together by gravitational force.

The distribution of the stars in a galaxy can give it a shape such as spiral, ring or elliptical. Our sun is a part of a spiral galaxy called the Milky Way Galaxy. This galaxy is named after the Milky Way. The Milky Way is a band of stars that we can see on a clear night. These stars are a part of our galaxy. The ancient Romans called this band of stars Via Galactica, or ‘road of milk’. That is how our galaxy got its name.

Constellations :

As the earth moves round the sun, we see different stars at different times of the year. In the past, people found many uses for this. For example, they would get ready for sowing when particular stars appeared in the sky. Obviously, it was not possible for them to identify each and every star. So, they looked for groups of stars which seem to form patterns in the sky. A group of stars which seem to form a pattern is called a constellation.

Ancient stargazers made stories about the constellations and named them after the animals, heroes, etc., from these stories. So constellations got names like Cygnus (swan), Leo (lion), Taurus (bull), Cancer (crab), Perseus (a hero) and Libra (scale). You can see many of these constellations on a clear night.

The Great Bear (Ursa Major) is one of the easiest constellations to spot. You can see it between February and May. Its seven brightest stars form the shape of a dipper (a long-handled spoon used for drawing out water). Together, these stars are called the Big Dipper or Saptarshi. These and the other stars of the constellation roughly form the shape of a bear.

The two brightest stars of the Big Dipper are called ‘pointers’ because they point towards the pole star. The pole star lies at the tail of the bear of a smaller constellation called the Little Bear (Ursa Minor).

To find the north direction, ancient travellers would look for the Big Dipper and from there, locate the pole star. While all stars seem to move from the east to the west (as the earth rotates in the opposite direction), the pole star seems fixed. This is because it lies almost directly above the earth’s North Pole [Figure 13.3 (c)].

Orion (the Hunter) and Scorpius are two other prominent constellations. There are different stories linking them. According to one, the mighty hunter Orion vowed to kill all the animals of the world. Alarmed at this, the Earth Goddess sent a scorpion to kill Orion. He ran away, and continues to do so even now. This story takes into account the fact that Orion goes below the horizon when Scorpius rises. Orion rises again only when Scorpius sets.

Remember that constellations are imaginary. For our convenience we have picked a few stars that resemble a pattern and called them a constellation. On the other hand, galaxies are real things in which stars and other celestial bodies are held together by gravitational force.

The Solar System :

The sun is the brightest object in the sky. It is huge. It is about 333,000 times heavier than the earth, and you could fit more than a million earths inside it! Its great mass causes a large gravitational force. This keeps the sun, the planets, their moons and some other smaller bodies together as the sun’s family. The sun and all the bodies moving around it are together called the solar system. All the members of the solar system revolve around the sun in almost circular paths, or orbits.

After the sun, the planets are the largest bodies in our solar system. Scientists define a planet as a round body that orbits the sun and which has pulled in all objects near its orbit. Remember that planets were formed when large bodies in space pulled in smaller bodies near it. This cleared the space around a planet’s orbit.

There are eight planets in our solar system. In order of distance from the sun they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. You can remember this order as My Very Efficient Maid Just Served Us Noodles.

Apart from revolving around the sun, each planet rotates, or spins, about its axis. The time taken to complete a revolution around the sun is the length of a planet’s year. And the time taken to complete one rotation is the planet’s day.

The four planets closest to the sun—Mercury, Venus, Earth and Mars—are small, rocky planets. They are called terrestrial (earthlike) planets. The other four planets—Jupiter, Saturn, Uranus and Neptune—are giants in comparison.

They are made up mainly of gases. They are called gas giants or Jovian (Jupiter like) planets. All the gas giants have rings around them. Since they are very far from the sun, the gas giants are much colder than the terrestrial planets.

While stars twinkle, planets shine with a steady light. You can see some of the planets with the naked eyes or with the help of a good pair of binoculars. Just remember that as the planets move around the sun, they appear at different positions in the sky at different times of the year. And for the period they are behind the sun, they are not visible.

Mercury, the smallest planet of our solar system, revolves around the sun the fastest. But it rotates on its axis at a much slower speed than the earth. So, a day on Mercury is about 58 times longer than a day on earth.

Although Mercury is the closest to the sun, it is not the hottest planet. Its thin atmosphere cannot trap heat. So, at night, when there is no sun, the temperature can fall to as low as -180°C. You can see Mercury near the eastern horizon before sunrise at certain times of the year. And at certain other times, you can see it near the western horizon after sunset.

The thick atmosphere of Venus makes it the brightest and the hottest planet of the solar system. Its atmosphere has mainly carbon dioxide gas, which reflects a lot of sunlight. But it also traps so much heat that the average temperature on Venus is about 450°C.

Venus takes 243 days to complete one rotation, making its day the longest in the solar system. As a matter of fact, a day on Venus is longer than its year! It is easy to spot Venus because it is so bright. When it is visible in the east before sunrise, it is called a morning star. And when it is visible in the west in the evening, it is called an evening star.

The earth is not the fastest, slowest, hottest, coldest, largest or smallest planet. But it is the only planet on which life is known to exist. The planet’s distance from the sun, the composition of its atmosphere and the fact that liquid water is found on it make life possible on it.

Were it nearer the sun, the water on it would have evaporated. Were it farther away, all our oceans, rivers and lakes would have frozen. The carbon dioxide in the earth’s atmosphere plays two important roles. Plants use it to make food—which feeds, directly or indirectly, all animals. It also traps just enough heat to ensure that the nights on earth do not become freezing cold.

No other planet evokes so much interest as Mars does. This is because scientists have found evidence that liquid water once flowed through the channels visible on its surface. So it is possible that some form of life once existed on this planet. The rust-coloured soil of Mars gives it a red colour. So, it is also called the Red Planet.

When visible, Mars looks like a red sphere. During its two-year orbit, it looks the brightest when the earth is between the sun and Mars. During this time, you can see it rise in the east as the sun sets in the west.

Jupiter is the largest and the heaviest planet of our solar system. It also has the largest number of moons. The strong winds blowing on it, and on the other gas giants, create light and dark areas, giving them a striped look.

If you look through a powerful telescope, you will see a big spot on Jupiter’s surface. This spot is actually a huge storm, which has been raging on Jupiter for more than 300 years. In 1979, the Voyager 1 spacecraft discovered faint rings around Jupiter. These rings are not visible even through the most powerful earth-based telescopes. Jupiter is also visible to the naked eye. It looks like a bright spot in the sky.

You can easily recognise a picture of Saturn because of the planet’s prominent rings. These rings are actually particles of dust and ice revolving around Saturn. Apart from these particles, a large number of moons orbit this planet.

Uranus and Neptune:

Uranus and Neptune are the third and the fourth largest planets respectively. Yet, they were the last two planets to be discovered. That is because they are so far away from us. Even today, we know very little about them.

The moons of planets :

An object revolving around a celestial body is known as a satellite. All planets except Mercury and Venus have natural satellites, or moons, revolving around them. So far, we know of more than 150 planetary moons. Some of them are so small that they were discovered only when spacecraft flew past them. A few of the moons are almost as large as planets. One of Jupiter’s moons, Ganymede, is the largest of them all. It is even larger than Mercury. Of all the moons, we know the most about the earth’s moon.

The earth’s moon:

The earth’s moon is the brightest object in the night sky. It shines by reflecting sunlight. If you look at the moon through a telescope or a good pair of binoculars, you will see a number of craters on its surface. These are large depressions created when huge rocks from space hit the moon. The moon does not have water or an atmosphere. It also does not have life on it.

The moon takes 27 days and 8 hours to complete one revolution around the earth. In this time it also completes one rotation around its axis. We see different shapes of the moon as it travels around the earth.

Stand in front of a lamp in a darkened room. Hold a ball in your outstretched arm and move it around you, just as the moon moves around the earth. A friend standing some distance away from you will always see half of the ball (moon) lit by the lamp (sun). But to you (earth) the shape of the lit portion will keep on changing, like the changing shapes of the moon.

Sunlight lights up half of the moon. As the moon revolves around the earth, we see different parts of the sunlit half. The shapes of these parts are called the phases of the moon. When the entire side facing the earth is sunlit, the moon appears as a full disc. We call this the full moon or purnima. And when the side of the moon facing us gets no sunlight, we do not see the moon.

This is called the new moon or amavasya. After the new moon, the moon appears as a thin crescent. As days pass, we see larger portions of the moon till the full moon appears. After this, the size of the moon visible to us gradually decreases till we once again have the new moon. The whole cycle of one new moon to the next takes 29.5 days. So the new moon and the full moon appear about fifteen days from each other.

Dwarf planets :

A dwarf planet is a small, round body that orbits the sun. At the time of its formation, a dwarf planet could not pull in all other objects near its orbit. So it is not considered a planet. Pluto, which was previously considered a planet, is now considered a dwarf planet. Ceres and Eris are two other dwarf planets.

Asteroids :

In a belt between the orbits of Mars and Jupiter, millions of small, irregular, rocky bodies revolve around the sun. These are asteroids, and the belt is known as the asteroid belt. Asteroids are also called minor planets.

Scientists think that asteroids are pieces of material that failed to come together to form a planet when the solar system was being formed. Asteroids can measure a few metres to hundreds of kilometres in width. Some asteroids even have moons.

Meteoroids :

Asteroids were not the only pieces of rock left over from the formation of the solar system. Some others, called meteoroids, still orbit the sun. When they come very close to a planet such as the earth, gravitation pulls them in.

As they enter the earth’s atmosphere, they heat up because of friction with the air, and start burning. As these burning meteoroids fall towards the ground, we see them as streaks of light. The streak of light caused by a burning meteoroid is called a meteor or a shooting star.

Fortunately, the material of most meteoroids burns up completely before it can reach the surface of the earth. However, some large ones fail to burn up completely and strike the earth’s surface. Meteoroids that fall on a planet or a moon are called meteorites. A large meteorite can create a large crater and cause a lot of damage.

Scientists think that dinosaurs were wiped off the earth following a meteorite hit. Meteorite hits are more common on those planets and moons which have little or no atmosphere to burn off the falling rock. The craters on our moon have resulted from meteorite hits.

A comet is a small body of ice and dust that moves around the sun in an elongated orbit. As a comet approaches the sun, it heats up and leaves behind a stream of hot, glowing gases and dust particles. We see this as the ‘tail’ of the comet.

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Cogitating black holes

The universe cannot always be understood through observation. instead, physicists explore by devising thought experiments.

by Michael Dine   + BIO

Albert Einstein’s theory of gravitation, known as general relativity, is intimidating, even for highly trained theoretical physicists. In his theory, matter and energy cause space-time to curve. In most situations, this warping is so small as to be unobservable, even with powerful and sophisticated instruments. In fact, for many years after Einstein put forth his theory in 1916, there were only three situations in which small corrections to Newton’s classic laws of gravity (the force we feel here on Earth) could be observed: the bending of light by the Sun during a solar eclipse; a small anomaly in the motion of Mercury; and a small shift in the wavelength of light due to gravitation. Since that time, the situation has dramatically changed. General relativity has provided us with a framework for thinking about the Universe as a whole, and plays a role in much of what astronomers understand about stars. It even plays a role in the GPS system that helps us navigate the roads.

Einstein’s equations ultimately revealed a set of previously unknown, ultradense cosmological objects: black holes. The mathematics of Einstein’s equations showed that light starting inside the black hole could get only so far. That distance, known as the Schwarzschild radius, can be thought of as the surface of the black hole; this surface is known as the horizon, beyond which light cannot escape. Near and within the horizon, space and time are modified so violently that it even becomes tricky to figure out what is space and what is time.

No one could see inside this kind of object, but speculations on their nature date to the work of J Robert Oppenheimer (famed for his leadership of the atomic bomb project during the Second World War) and John Wheeler, a Princeton theorist who provided, among other things, the name ‘black hole’.

Over the past half-century, astronomers have found black holes in great numbers around the Universe. Some are the result of stellar collapse, and have masses typically a few times larger than that of our Sun. Much more massive ones exist at the centres of most galaxies, including our own. Smaller black holes are typically ‘seen’ as they swallow matter from companion stars; the large black hole at the centre of our galaxy was discovered through its effects on the motion of stars orbiting about it. We may never be able to literally peer inside a black hole, but knowledge of the cosmos and emerging theories of physics allow us to think through their nature; the modus operandi for this kind of exploration, the thought experiment, has been a cornerstone of physics since Einstein dramatically altered our understanding of space and time.

E instein’s theory that the Universe is curved and time is relative has been subject to direct experimental and observational study for more than a century – but thought experiments played a major role, as well. One of the most famous thought experiments of all time juxtaposed Einstein’s general relativity, which looked at systems as large as the cosmos, with quantum mechanics, also referred to as quantum theory, which resulted from experimental studies of objects on the scale of atoms or smaller.

Prior to the emergence of quantum mechanics, physicists thought of atoms as something like billiard balls. In the pre-quantum or classical view, their motion was governed by Isaac Newton’s laws, which allow a person, given knowledge of the basic forces of nature, to predict the motion of the particles in the future. But quantum mechanics called this viewpoint into question. Instead, it suggested an alternative picture of reality, coded in the Schrödinger equation – which provided the probability, though not the certainty, that an electron would be located at a given spot at a particular point in time. It was the physicist Max Born who made the radical proposal that quantum mechanics predicted probabilities of various outcomes, rather than a single certain result. Critical to his assertion was a set of thought experiments. Born asked what Schrödinger’s equation would predict for the outcome of the collision between two atoms, or an atom and an electron. Newton’s billiard ball outlook holds only when the probability of one particular outcome is far larger than that of any other.

Thought experiments suggested the widely separated elements would still be entangled

The notion deeply troubled Einstein, provoking his complaint in a letter to Born in December 1926: ‘Quantum mechanics is certainly imposing… The theory says a lot, but does not really bring us any closer to the secret of the “old one”. I, at any rate, am convinced that He does not throw dice.’

In 1927, Werner Heisenberg summarised the distinctions between the physics of Newton and that of the Schrödinger equation in his uncertainty principle, which sets limits on what one can measure about a system. The location of a particle, would always be a question of probability, never a sure thing. He arrived at this principle by considering various thought experiments, where he asked how particular measurements might actually be performed. Einstein tried to demolish the quantum theory through sharp critique, continually challenging Niels Bohr , a Danish founder of quantum mechanics and a leader in the effort to interpret the theory with thought experiments similar to those of Born and Heisenberg. At first glance, these seemed to show that quantum theory and its probability interpretation did not make sense. The questions Einstein asked were often tough, but Bohr, sometimes after a prolonged period of thought, invariably found a way to resolve each paradox. One such experiment, known as the EPR paradox (for Einstein and his two assistants, Boris Podolsky and Nathan Rosen), involved the connections between two widely separated parts of a single system. Thought experiments suggested the widely separated elements would still be entangled, with one part of the system invariably providing information about the other. This was eventually turned into a real experiment, proving quantum mechanics correct.

S o what does all this have to do with black holes? A real-world experiment sets the stage.

According to the rules of classical physics, an object with electric charge, like an electron or proton, emits light as it speeds up or slows down. Einstein understood that, in a similar manner, his general relativity would lead to waves of the gravitational field – gravity waves – when mass or other forms of energy sped up or slowed down. These waves, in turn, would push and pull on matter as they passed by. Because the gravitational force is so much weaker than electricity and magnetism, these effects would be minuscule, even when huge amounts of mass are involved.

The first experimental programme with any real hope to detect these tiny gravitational waves began in the 1990s, and was known as LIGO, for Laser Interferometer Gravitational-Wave Observatory.

The programme was based on an outcome of general relativity understood early on by Einstein: when two planets collide, the mass involved would be insufficient to perceptibly impact the shape of space-time. But when two superdense objects like black holes collide, they would distort space-time enough that the effect could be detected. According to Einstein’s theory, these waves, travelling through space from their source, would stretch the space around them, ever so slightly. Objects nearby would appear slightly longer and then slightly shorter, and then slightly longer again. This stretching and shrinking would alert us that the objects had been there at all.

Now, when I say slightly, I mean slightly . The LIGO gravitational-wave detectors are long metal tubes each 4 kilometres long. Waves from colliding black holes stretch and shrink these huge bars by about 10 -18 cm, an amount 10 5 times – 100,000 times – smaller than an atomic nucleus. Put another way, as a fraction of its length, each bar changes by about a trillionth of a trillionth of its length.

Throw in tables, chairs, planets, other stars, and the black hole’s mass increases and its horizon area increases

Only over the past decade has the detector picked up gravitational waves from collisions of neutron stars and black holes. With this discovery, a whole new way to study the Universe has emerged .

Yet these experiments go only so far. Indeed, in a universe governed by quantum mechanics, there are aspects of black holes that are far from clear. Because, in Einstein’s theory, a black hole can’t emit light or transmit information in other ways, they are almost featureless. If you know their mass, their electric charge, and how fast they spin, you know everything you can possibly know about them. They may have arisen from the collapse of a complicated star, surrounded by planets with advanced civilisations, but when they formed, all of that information simply vanished. This is different from a fire or an explosion, where you might hope, with a huge amount of work, to reconstruct all the original information by looking through the ashes and the outgoing light and heat. In the collapse of a black hole, such reconstruction seems impossible.

This new visualisation of a black hole illustrates how its gravity distorts our view, warping its surroundings as if seen in a carnival mirror. The visualisation simulates the appearance of a black hole where infalling matter has collected into a thin, hot structure called an accretion disk. The black hole’s extreme gravity skews light emitted by different regions of the disk, producing the misshapen appearance. Created by NASA Goddard Space Flight Center/Jeremy Schnittman

One physicist who tried to glean more through thought experiment was the late theorist Jacob Bekenstein of the Hebrew University of Jerusalem. He noted an analogy between black holes and the second law of thermodynamics. The second law says that entropy – which is a measure of disorder – always increases. For black holes, there is also a quantity that always increases: the area of the black hole surface, its horizon. Whenever you add something to a black hole – say throwing in tables, chairs, planets, other stars – the mass increases and the area of the horizon increases. Bekenstein proposed a precise relationship between the black hole area and entropy, and suggested that black holes were actually thermodynamic systems with a temperature.

In physics, we think of temperature as a measure of the energy within some set of particles – atoms, molecules, photons. Yet, from the outside, we have no information about the black hole apart from some gross properties such as its mass, and we certainly can’t identify things like particles.

It was Stephen Hawking who, in the early stages of his career, finally discovered the sense in which black holes have a temperature. Hawking had an interest in extreme situations in general relativity, such as the earliest instants after the Big Bang and the interior of black holes. Now thinking about the behaviour of particles such as electrons and photons near the horizon of a black hole – thought experiments again – he realised that black holes are not really black; they radiate particles now known as the ‘Hawking radiation’. This is an intrinsically quantum phenomenon. The uncertainty principle permits brief violations of energy conservation in ordinary space-time. As a result, for an extremely short time, a particle and its antiparticle (in the case of an electron, for example, the antiparticle has the same mass but the opposite electric charge, known as the positron) can appear, even in a complete vacuum, and then annihilate each other and disappear again. For us, there is no observable consequence because energy is conserved.

But Hawking realised that some of these flickering particles could borrow some of the enormous energy of the black hole and become real. If produced near the horizon, one of these virtual particles could fall back into the black hole while the other escapes. Hawking found that the particles were emitted just as they would be from an object with the temperature predicted by Bekenstein. (The radiation from an object with a given temperature is called ‘blackbody radiation’ and has characteristic features; the most dramatic example is the Universe itself, whose temperature is 2.7 degrees Kelvin).

In short, the black hole appears to be a much more complicated object in a quantum world than in a classical one. In the quantum world, there’s a lot going on inside. The black hole in the quantum universe is not static. As it emits particles, it gradually evaporates, eventually disappearing altogether.

For a black hole formed in the collapse of a star a bit more massive than our Sun, the time for the entire object to evaporate is very long – about 10 67 years, far, far longer than the present age of the Universe. But we can contemplate smaller black holes, which might be disappearing today. At the end of their lifetimes, there would be a large burst of energy. Astrophysicists are currently searching for this possibility. But we’d have to be quite lucky to find such a thing and, so far, there is no evidence for black holes of this size.

H awking’s theoretical discovery of the Hawking radiation, possible through thought experiment, was a major accomplishment. It brought general relativity and quantum theory together in a remarkable way. But performing still another thought experiment, Hawking was puzzled by features of this radiation – or more precisely, its lack of features. Critical to Born’s probability interpretation of quantum mechanics was that something always happens. If you add up the probabilities for anything that may happen, you will find that the total probability is one. This can be formulated as a statement about information: if one knows everything one can know about a system at one time, one can know everything about it at later times. But this did not seem to be the case for radiation from black holes.

These ideas may be unfamiliar – indeed they are unclear to many physicists, so it is worth elaborating a bit. The fact that the probability of all outcomes is one is illustrated by a familiar pastime. If you enter your state or national lottery, you focus on your chances of winning. If you buy one ticket and there are 10 million lottery tickets sold, your chances of winning the jackpot are 1 in 10 million. That’s a really minute chance. But I either win or lose the lottery: the chance of winning or losing is 100 per cent.

What does it mean for information to disappear? Of course, we all forget things, lose records of various types, or deliberately shred or burn papers. But we believe that with enough patience and resources, we could reconstruct this information. The amount of information in a system (or the Universe) doesn’t change, though much of it may be hard to access. For a complicated system, like a collapsing star, there is a lot of information – an unimaginably large amount. In classical physics, there would be the positions and velocities of all the nuclei and electrons. In quantum mechanics, there are complicated relations between all of them; one can’t give the probability that one particle is at a point without specifying also the probability of finding all the other particles at particular places as well.

There is a situation where black holes could exist and quantum mechanics could make sense: string theory

So a collapsing star contains a huge amount of information. Thanks to Hawking, we know that, if the star is heavy enough, it forms a black hole and then slowly evaporates, emitting radiation. The vast amount of information that was contained in the initial star has been reduced to just the temperature of a warm body. Hawking, in his 1976 paper , argued that the information was simply lost. Quantum mechanics, he asserted, breaks down near black holes.

Many leading theorists have struggled to resolve the puzzles raised by this thought experiment. Some have argued that, indeed, one has to redo quantum mechanics or general relativity to resolve Hawking’s paradox. Others have been more sceptical of Hawking. Perhaps, for example, the evaporation of a black hole is like a lump of ash from the burning of a log in a fireplace. Surely the laws of quantum mechanics don’t break down when an object burns? In that case, the resolution of the puzzle is that the outgoing radiation is not exactly that of a black body because subtle connections between the outgoing photons remain intact. But it was soon realised that the answer to Hawking’s question about the black hole problem could not be so simple; the structure of space and time makes it hard to understand how such correlations might arise. There were other proposals, none very satisfying. Perhaps Hawking was right: just as Newtonian physics was usurped by quantum mechanics and general relativity on large or tiny scales, something had to give here as well.

It turns out that there is a situation where black holes could exist and quantum mechanics could make sense: string theory. String theory, also emerging from thought experiments, replaces the particles of quantum mechanics with one-dimensional strings. That concept has provided at least a partial resolution of the puzzle. Two theorists at Harvard University – Cumrun Vafa and Andrew Strominger – building on the work of the late Joseph Polchinski, of the University of California at Santa Barbara, were able to understand the temperature of certain idealised black holes in quantum mechanical terms. In other words, the information, at least for these idealised systems, somehow survives, evading Hawking’s paradox.

But while this result settled the question in an abstract way, it left many physicists dissatisfied. Because the calculation is done in a situation that doesn’t much resemble an astrophysical black hole, it is hard to figure out just what went wrong with Hawking’s argument.

There remains something important about the way general relativity works that we don’t yet fully understand. It may be that the rest of the story will be rather mundane, but it seems likely that fully resolving these questions will yield dramatic new insights into the quantum nature of space-time, and might answer some big questions we have about the Universe as we observe it. One of the biggest puzzles in our current understanding of nature is that most of the energy of the Universe – about 70 per cent – exists in a strange form with negative pressure , known as the dark energy . But it is very hard to understand why there is so little of it.

It is conceivable that a thought experiment resolving Hawking’s puzzle might provide some clues. The most radical possibility is that space-time is not the basic arena for the phenomena of nature. A being living in a crystal, for instance, would experience something like space-time, but would have a very different character. Condensed matter physicists would say that space-time is emergent. The basic underlying entity might be something else entirely. Perhaps one day our science and technology will be so advanced that actual experiments will reveal what it is – but, until then, thought experiments involving black holes, among other phenomena, will have to light the way.

Adapted excerpt from the book This Way to the Universe by Michael Dine, published by Dutton, an imprint of Penguin Publishing Group, a division of Penguin Random House LLC. Copyright © 2022 by Michael Dine

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“Are We Alone in the Universe?” Winston Churchill’s Lost Extraterrestrial Essay Says No

The famed British statesman approached the question of alien life with a scientist’s mind

Brian Handwerk

Science Correspondent

Winston Churchill, British prime minister and one of history’s most influential statesmen, was undoubtedly a man with weighty questions on his mind. How best to save the British Empire? he must have mused. What will the postwar world look like? he surely wondered. But the legendary leader also focused his prodigious mind on less pragmatic questions. For instance: Is there life on other planets?

In fact, in 1939, Churchill penned a lengthy essay on this very topic, which was never published. Besides displaying a strong grasp of contemporary astrophysics and a scientific mind, he came to a breathtaking conclusion: We are probably not alone in the universe. The long-lost piece of Churchilliana has just floated up to the surface again, thanks to an article  written by astrophysicist Mario Livio in this week's edition of the journal Nature analyzing Churchill's work. 

“With hundreds of thousands of nebulae, each containing thousands of millions of suns, the odds are enormous that there must be immense numbers which possess planets whose circumstances would not render life impossible,” Churchill concluded in his essay. He wrote these words on the eve of World War II—more than half a century before exoplanets were discovered.  

Until last year, Churchill's thoughts on the problem of alien life had been all but lost to history. The reason: His 11-page typed draft was never published. Sometime in the late 1950s, Churchill revised the essay while visiting the seaside villa of publisher Emery Reves, but the text still didn't see the light of day. It appears to have languished in the Reves house until Emery's wife Wendy gave it to the U.S. National Churchill Museum during the 1980s.

Last year, the museum’s new director, Timothy Riley, unearthed the essay in the museum's archives. When astrophysicist  Mario Livio  happened to visit the museum, Riley "thrust [the] typewritten essay" into his hands, Livio writes in Nature. Riley was eager to hear the perspective of an astrophysicist. And Livio, for his part, was floored. “Imagine my thrill that I may be the first scientist to examine this essay,” he writes in Nature.

Churchill did his homework, Livio reports. Though he probably didn't pore over peer-reviewed scientific literature, the statesman seems to have read enough, and spoke with enough top scientists—including the physicist Frederick Lindemann, his friend and later his official scientific adviser—to have had a strong grasp of the major theories and ideas of his time. But that wasn't what left the deepest impression on Livio.

“To me the most impressive part of the essay—other than the fact that he was interested in it at all, which is pretty remarkable—is really the way that he thinks,” Livio says. “He approached the problem just as a scientist today would. To answer his question 'Are we alone in the universe?' he started by defining life. Then he said, 'OK, what does life require? What are the necessary conditions for life to exist?'”

Churchill identified liquid water, for example, as a primary requirement. While he acknowledged the possibility that forms of life could exist dependent on some other liquid, he concluded that “nothing in our present knowledge entitles us to make such an assumption.”  

"This is exactly what we still do today: Try to find life by following the water,” Livio says. “But next, Churchill asked 'What does it take for liquid water to be there?' And so he identified this thing that today we call the habitable zone.”

By breaking down the challenge into its component parts, Churchill ended up delving into the factors necessary to create what is now known as the “Goldilocks zone” around a star: that elusive region in which a life-sustaining planet could theoretically exist. In our own solar system, he concluded, only Mars and Venus could possibly harbor life outside of Earth. The other planets don't have the right temperatures, Churchill noted, while the Moon and asteroids lack sufficient gravity to trap gasses and sustain atmospheres.

Turning his gaze beyond our own solar system raised even more possibilities for life, at least in Churchill's mind. “The sun is merely one star in our galaxy, which contains several thousand millions of others,” he wrote. Planetary formation would be rather rare around those stars, he admitted, drawing on a then-popular theory of noted physicist and astronomer James Jeans. But what if that theory turned out to be incorrect? (In fact, it has now been disproven.)

“That's what I find really fascinating,” Livio notes. “The healthy skepticism that he displayed is remarkable.”

Churchill suggested that different planetary formation theories may mean that many such planets may exist which “will be the right size to keep on their surface water and possibly an atmosphere of some sort.” Of that group, some may also be “at the proper distance from their parent sun to maintain a suitable temperature.”

The statesman even expected that some day, “possibly even in the not very distant future,” visitors might see for themselves whether there is life on the moon, or even Mars.

But what was Winston Churchill doing penning a lengthy essay on the probability of alien life in the first place? After all, it was the eve of a war that would decide the fate of the free world, and Churchill was about to become Prime Minister of the United Kingdom.

Such an undertaking was actually quite typical for Churchill, notes Andrew Nahum, Keeper Emeritus at the Science Museum, London, because it reflects both his scientific curiosity and his recurring need to write for money. It was skill with the pen that often supported Churchill and his family's lavish lifestyle (recall that he won the 1953 Nobel Prize for Literature, with a monetary award of 175,293 Swedish Kroner worth about $275,000 today).

“One recent biography is entitled No More Champagne: Churchill And His Money,” Nahum says. “That was a phrase he put into a note to his wife about austerity measures. But he didn't know much about austerity. He liked luxury so he wrote like crazy, both books and articles that his agent circulated widely.”  

That’s not to say that Churchill was simply slinging copy about aliens for a paycheck. “He was profoundly interested in the sciences and he read very widely,” notes Nahum, who curated the 2015 Science Museum exhibition “ Churchill's Scientists .” Nahum relates the tale of how as Chancellor of the Exchequer, Churchill was once sent a book on quantum physics, and later admitted that it had occupied him for the better part of a day that should have been spent balancing the British budget.

He not only read scientific content voraciously, but wrote on the topic as well. In a 1924 issue of Nash's Pall Mall Magazine, Churchill anticipated the power of atomic weapons. “Might not a bomb no bigger than an orange be found to possess secret power to destroy a whole block of buildings nay, to blast a township at a stroke?” he warned. In 1932, he anticipated the rise of test-tube meat in the magazine  Popular Mechanics: “Fifty years hence, we shall escape the absurdity of growing a whole chicken in order to eat the breast or the wing, by growing these parts separately in a suitable medium,” he wrote.

In 1939 he authored three essays, tackling not just extraterrestrial life but the evolution of life on Earth and the popular biology of the human body. Two were published during 1942 by the Sunday Dispatch , Nahum discovered when reading Churchill's papers at the University of Cambridge. It remains a mystery why his thoughts on alien life went unpublished.

In the rediscovered essay, Churchill admits that, because of the great distances between us and other planet-harboring stars, we may never know if his hunch that life is scattered among the vastness of the cosmos is correct. Yet even without proof, Churchill seems to have convinced himself that such a possibility was likely—perhaps by swapping his scientific mind for one more finely attuned to the human condition during the troubled 20th century.

“I, for one, am not so immensely impressed by the success we are making of our civilization here that I am prepared to think we are the only spot in this immense universe which contains living, thinking creatures,” he wrote, “or that we are the highest type of mental and physical development which has ever appeared in the vast compass of space and time.”

Seventy-five years after Churchill's bold speculations, there's still no proof that life exists on other worlds. But, as was often the case, his analysis of our own still seems prescient.

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Brian Handwerk | READ MORE

Brian Handwerk is a science correspondent based in Amherst, New Hampshire.

• Essay Editor

How to End a College Essay: Strategies and Examples

Writing a college essay takes skill, but making a strong college essay conclusion is often the most important part. A great ending can make a big impact on your readers and bring your main ideas together. This guide will walk you through four strategies that will help you create impactful conclusions that resonate with your audience.

1. Writing a Memorable College Essay Conclusion

The conclusion of your essay is your last chance to strengthen your main points and leave a lasting impression. A well-written ending can make your whole essay better and more memorable.

Successful Essay Ending Examples

Here are some great ways to end an essay:

• Share a thoughtful idea that connects to your main point, giving a sense of closure and understanding.
• Quickly go over your main points, showing them in a new way.
• Discuss why your topic matters beyond just your essay.
• Link back to your introduction, making your writing feel complete.

Example: 

"When I started looking into how music affects the brain, I didn't know I'd find a connection to my grandmother's struggle with Alzheimer's. I learned that songs people know well can often bring back memories for patients, even when they have trouble talking. This discovery changed how I see music's power and gave me a new way to connect with my grandmother. When we hum her favorite songs together, I see hints of recognition in her eyes, reminding me that sometimes, big scientific ideas can have very personal effects."

Common Mistakes in Ending an Essay

Avoid these problems when writing your college essay conclusion:

• Adding new ideas: Your conclusion should bring together existing points, not introduce new information.
• Just repeating your main point: While it's important to remind readers of your main idea, simply saying it again word-for-word doesn't work well.
• Using overused phrases: Don't use expressions like "In conclusion" or "To sum up."
• Stopping too suddenly: Make sure your conclusion gives a feeling of completion and doesn't leave readers hanging.

Aithor's advanced language model can help you write compelling conclusions that avoid these common mistakes and enhance the overall impact of your essay.

2. Thought-Provoking Questions: A Powerful Way to End an Essay

Ending an essay with a question that makes people think can get your readers interested and encourage them to keep thinking about your topic. This approach leaves a strong impression and can make your essay more memorable.

"After looking at how social media changes how we see ourselves, we're left with an important question: Can we find a way to share our lives online while still living them fully offline? Maybe the answer isn't choosing between the online and real worlds, but learning how to connect well in both."

When using this method, make sure your question is:

• Related to your essay's main topic
• Open-ended, encouraging deeper thought
• Not easy to answer with just "yes" or "no"

3. How to End Your College Essay with a Call to Action

A call to action (CTA) in your conclusion can encourage your readers to do something based on the ideas you've talked about. This works well for essays about social issues, environmental problems, or personal growth topics.

"In this essay, we've looked at the problem of plastic in our oceans. Now, it's time to help fix it. Start by replacing one single-use plastic item you use every day with something you can use again. It could be as simple as using a reusable water bottle or bringing your own bags to the store. Tell your friends and family what you're doing. By taking these small steps, we're not just making less waste; we're starting a chain reaction that can lead to cleaner oceans and a healthier planet."

When writing a CTA for your college essay conclusion, make sure it's:

• Clear and easy to write
• Directly related to your essay's main points
• Something your readers can actually do

Aithor can assist you in writing perfect calls to action that connect with your readers and fit well with your essay's content.

4. Personal Anecdotes: An Engaging Essay Ending

Ending an essay with a personal story can help your readers feel connected to you and strengthen your main message. This approach makes your writing more relatable and human.

"Last summer, I helped at a local animal shelter. One day, they brought in an older, scruffy dog named Max. For weeks, people passed him by, always choosing younger, cuter puppies instead. I started spending extra time with Max, and slowly, his playful side came out. When a family finally took him home, the happiness on their faces – and Max's wagging tail – showed me how important it is to give every living thing a chance. This taught me more about patience, unfair judgments, and the power of second chances than any book ever could."

When using a personal story to end your college essay:

• Make sure it relates to your main topic
• Keep it short and powerful
• Use clear language to paint a picture for your readers

Tips on How to End a College Essay

To write a strong conclusion, think about these extra tips on how to end a college essay:

• Wrap up your main points clearly while suggesting how they might apply to other things or future ideas to keep your readers thinking.
• Make sure your conclusion sounds like the rest of your essay for a smooth, polished finish.
• Don't weaken your arguments by sounding unsure in your conclusion.
• Be extra careful with grammar and punctuation in your conclusion, as it's the last thing your readers will remember.
• Write your conclusion to connect with your specific readers, whether they're college admissions staff, teachers, or other students.
• Write a short and powerful conclusion that drives your main points home without repeating too much or using too many words.

Remember, your conclusion is your last chance to make a strong impression. Take your time to write it carefully, making sure it ties together your main points and shows why your essay matters.

For those wondering how to end a reflection paper, Aithor can help you improve your college essay conclusion, making sure it's polished, powerful, and fits your specific needs. This top writing tool can help you refine your essay ending examples and give you guidance on how to end a reflection paper or any other type of school writing.

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Winner Announcement: TGC’s 2024 Essay Contest for Young Adults

More by staff.

Gen Z is a generation that faces the temptation to avoid hard things. With phones to hide behind, it’s easier than ever to get lost in a virtual world instead of facing the real world . Scripture tells us we shouldn’t be surprised when we face trials in this life as if something strange were happening to us, and that we can even rejoice in trials (1 Pet. 1:6–7; 4:12–13). Our young writers are learning this countercultural lesson. We have a God who cares more about our Christ-conformity than our comfort, and this is good news.

Over the past few months, we’ve had the privilege of reading the submissions to The Gospel Coalition’s 2024 Essay Contest for Young Adults . Nearly 200 young writers submitted original essays, and the editorial team reviewed them. These writers shared personal testimonies of their wrestling with God as they faced debilitating illness, societal pressure, and unfulfilled desires. We were impressed by their self-reflections on what they were pursuing more than God, whether it was acceptance into university, dream jobs, or the phones in their pockets.

Their writing displayed their desire to treasure Christ above all else.

Thoughtful Writers

The essays TGC received came from 183 young writers:

• They ranged in age from 16 to 22. Many were high school students; others were in college or just beginning their adult lives.
• As with last year’s contest , two-thirds of the writers were female.
• They’re members of local churches—Presbyterians, Baptists, and Anglicans predominated, with many nondenominational churches also represented.
• They submitted their essays from all over the U.S. and 14 other countries including Canada, South Africa, Malaysia, and the United Arab Emirates.

Many of these young writers poured out their hearts as they shared about times when God, in his love, withheld something from them. Others wrote of how they moved from clinging to their phones to clinging to Christ. Some shared how they see the need for men and women like themselves to give their lives to vocational ministry to reach the 3 billion people with no access to the gospel.

Our hearts were warmed as we read stories of Gen Z Christians refusing the lies their culture is feeding them. Instead, they’re inviting us to taste and see with them that the Lord is good (Ps. 34:8).

Personal Reflections

In TGC’s contest guidelines , we provided three prompts that allowed writers to reflect on their own lives as a means of speaking to their generation. Gen Zers are stereotypically called “screenagers” for spending a considerable amount of time on the internet. One prompt asked, “How has the gospel changed your relationship with your phone?” Many who chose this prompt were aware of their temptation to depend on their devices. They want to view their phones as tools, not as extra limbs.

Other writers shared why they’re considering full-time vocational ministry, knowing it’ll come at great cost. They’re willing to lay aside dream jobs with well-paying salaries for the sake of serving the Lord. Having to stand firm in the faith amid a deconstructing culture, they see themselves as equipped to reach their generation.

The most selected prompt was “When did the Lord love you by not giving you what you wanted?” By withholding something these young people wanted (though it was often a good thing), the Lord in his kindness revealed sin in their lives, drawing them closer to himself. What a beautiful picture of what our loving Father does for us, his children (Heb. 12:5–11).

We pray your hearts will be warmed and your souls edified as you read these essays (and TGC will be publishing more of them over the coming months).

Among the essays, three pieces stood out as well-crafted, thoughtful, and engaging. Our editorial team was clear about which winners to select, and we’re delighted to publish them on the site for you to read.

First Place: “ Who Was ‘i’ Without My iPhone? ” by Luke Simon

Luke opens his essay with these words: “Steve Jobs might’ve been a prophet. Or he at least predicted how his device would shape my future. After all, he placed the ‘i’ next to ‘Phone.’” Behind his screen, Luke Simon became luk3simon, forging a new identity and avoiding reality—and ultimately God. Eventually, he realized he needed a digital detox. Luke gives us practical ways to unhitch our identities from our phones, pointing us to the hope found in Jesus alone.

Second Place: “ How God’s ‘No’ to My Dream School Was a ‘Yes’ to the Local Church ” by Logan Watters

In her inspiring essay, Logan tells of how membership in a faithful, gospel-preaching church was a better pursuit than her dream school. And this made no sense to her friends. When we seek the Lord’s will and his plans above our own, the self-seeking world around us is left confused. Logan writes, “After a taste of [God’s] plans compared to mine, I don’t want anything else.”

Third Place: “ The Lord Loved Me by Giving Me a Broken Family ” by Karsten Harrison

In his essay, Karsten sees God’s love through unanswered prayer. Speaking to those who come from broken families, Karsten brings hope by pointing to the Lord’s steadfast love and the rich fellowship found with our church family. He writes, “God doesn’t simply give whatever we ask. Instead, we pray that his will would be accomplished, thus aligning our wills with his.” May we learn with him that God’s “No” always comes from his love for us and invites us to depend on him.

Take time today to read these essays and praise God for his faithfulness in his love toward us:

The steadfast love of the LORD never ceases; his mercies never come to an end; they are new every morning; great is your faithfulness. (Lam. 3:22–23)

Read more essays from young adults: 2022 and 2023 Contest Winners.

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Teachers' Day 2024: Ten Lines, Short and Long Essays For School Students

Published By : Suramya Sunilraj

Trending Desk

Last Updated: September 04, 2024, 09:00 IST

New Delhi, India

Students celebrate their teachers’ dedication and arduous work on this day by participating in exciting activities (Representative Image/ Shutterstock)

This special day encourages students to express their gratitude and admiration for their teachers, who have a significant impact on their lives and future

Teachers’ Day is an occasion set aside to celebrate and appreciate their hard work, dedication and contributions. Teachers’ Day is held every year on September 5 to commemorate the birth anniversary of Dr Sarvepalli Radhakrishnan, a prominent scholar, teacher and India’s second president. This special day encourages students to express their gratitude and admiration for their teachers, who have a significant impact on their lives and future.

Students celebrate their teachers’ dedication and arduous work on this day by participating in exciting activities and events such as delivering speeches and writing essays, making cards and posters, reciting poetry and slogans, engaging in fun games, and singing and dancing. Here are some simple essays to write and share with your adored teachers.

10 Lines Essay on Teacher’s Day (Primary Level):

– Teachers play an important role in our lives.

– In India, people celebrate this day on September 5 of every year.

– The Teacher’s Day celebration was started in 1962.

– The day is commemorated to honour Dr S Radhakrishnan, the first vice president and second president of India, on his birthday.

– In addition to being a renowned scholar, diplomat and President of India, he was also acommitted teacher.

– He stated that people shouldcelebrate September 5 as Teacher’s Day rather than his birthday.

– The teaching community is respected on this day and is widely observed across the country.

– To show love and appreciation for teachers, students make greeting cards and give presents.

– Schools and other institutions host a variety of events and programmes on this day.

– A few exceptional teachers get awarded with National Awards from the Ministry of Education in recognition of their outstanding work.

Teacher’s Day 2024: Short Essays 150 words (Secondary Level)

Every year on the birth anniversary of Dr Sarvapalli Radhakrishnan, India observes Teachers’ Day. He was deeply committed to the teaching profession. Some kids reportedly approached him and asked whether he wanted to celebrate his birthday on September 5. He then suggested that they honour all teachers on this day to mark their outstanding efforts and accomplishments. Teachers are the genuine builders of the nation’s future, influencing the lives of students, who in turn shape the nation’s destiny.

Teachers have an essential role in nation-building. However, one hardly recognises the necessity of teachers in the community. Teachers’ Day has been honoured on September 5 each year since 1962. Our teachers not only teach us, but they also help us develop our personalities, confidence and abilities. They assist us in overcoming whatever hurdles we may encounter in life. Here’s a Happy Teachers’ Day to all the hardworking teachers across India!

Teachers’ Day 2024: Long Essays 250 words (Higher Secondary Level)

Every year on September 5, students observe Teacher Day. It honours the birth anniversary of Dr Sarvepalli Radhakrishnan, India’s first Vice President and a dedicated teacher. He was a staunch promoter of education and was well-known for his work as a scholar, diplomat, educator and former President of India.

Teachers’ Day is a wonderful time to honour and cherish the relationship between teachers and students. Nowadays, students and instructors in schools, colleges, universities and other educational institutions exhibit their enthusiasm and excitement. Students often wish their teachers a long life. The relationship between teachers and students is something to be thankful for and treasure for a lifetime. These days, students and professors gladly participate in the celebrations at schools, colleges, universities and other educational institutions.

Students organise several events on Teachers’ Day to show respect for their teachers. These activities include cultural programmes, lectures, poems and small expressions of gratitude. Some students show their gratitude through heartfelt comments or notes. In some schools, senior students serve as instructors for the day, gaining experience with the problems and responsibilities of teaching.

We should recognise and cherish the teachers in our lives, and we should celebrate Teachers’ Day every year to express our gratitude for their work. Teachers, like our parents, help us develop our minds to thrive in life. And, it is our responsibility to honour them by adhering to all of their lessons and teachings. Happy Teachers’ Day to all!

• Dr Sarvepalli Radhakrishnan
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Edwidge Danticat's new collection of essays says 'We're Alone'

Ari Shapiro

Tinbete Ermyas

Jordan-Marie Smith

NPR's Ari Shapiro talks with author Edwidge Dandicat about her new essay collection, We're Alone .

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