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• How to Write a Strong Hypothesis | Steps & Examples

How to Write a Strong Hypothesis | Steps & Examples

Published on May 6, 2022 by Shona McCombes . Revised on November 20, 2023.

A hypothesis is a statement that can be tested by scientific research. If you want to test a relationship between two or more variables, you need to write hypotheses before you start your experiment or data collection .

Example: Hypothesis

Daily apple consumption leads to fewer doctor’s visits.

Table of contents

What is a hypothesis, developing a hypothesis (with example), hypothesis examples, other interesting articles, frequently asked questions about writing hypotheses.

A hypothesis states your predictions about what your research will find. It is a tentative answer to your research question that has not yet been tested. For some research projects, you might have to write several hypotheses that address different aspects of your research question.

A hypothesis is not just a guess – it should be based on existing theories and knowledge. It also has to be testable, which means you can support or refute it through scientific research methods (such as experiments, observations and statistical analysis of data).

Variables in hypotheses

Hypotheses propose a relationship between two or more types of variables .

• An independent variable is something the researcher changes or controls.
• A dependent variable is something the researcher observes and measures.

If there are any control variables , extraneous variables , or confounding variables , be sure to jot those down as you go to minimize the chances that research bias  will affect your results.

In this example, the independent variable is exposure to the sun – the assumed cause . The dependent variable is the level of happiness – the assumed effect .

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Step 1. ask a question.

Writing a hypothesis begins with a research question that you want to answer. The question should be focused, specific, and researchable within the constraints of your project.

Step 2. Do some preliminary research

Your initial answer to the question should be based on what is already known about the topic. Look for theories and previous studies to help you form educated assumptions about what your research will find.

At this stage, you might construct a conceptual framework to ensure that you’re embarking on a relevant topic . This can also help you identify which variables you will study and what you think the relationships are between them. Sometimes, you’ll have to operationalize more complex constructs.

Step 3. Formulate your hypothesis

Now you should have some idea of what you expect to find. Write your initial answer to the question in a clear, concise sentence.

4. Refine your hypothesis

You need to make sure your hypothesis is specific and testable. There are various ways of phrasing a hypothesis, but all the terms you use should have clear definitions, and the hypothesis should contain:

• The relevant variables
• The specific group being studied
• The predicted outcome of the experiment or analysis

5. Phrase your hypothesis in three ways

To identify the variables, you can write a simple prediction in  if…then form. The first part of the sentence states the independent variable and the second part states the dependent variable.

In academic research, hypotheses are more commonly phrased in terms of correlations or effects, where you directly state the predicted relationship between variables.

If you are comparing two groups, the hypothesis can state what difference you expect to find between them.

6. Write a null hypothesis

If your research involves statistical hypothesis testing , you will also have to write a null hypothesis . The null hypothesis is the default position that there is no association between the variables. The null hypothesis is written as H 0 , while the alternative hypothesis is H 1 or H a .

• H 0 : The number of lectures attended by first-year students has no effect on their final exam scores.
• H 1 : The number of lectures attended by first-year students has a positive effect on their final exam scores.

If you want to know more about the research process , methodology , research bias , or statistics , make sure to check out some of our other articles with explanations and examples.

• Sampling methods
• Simple random sampling
• Stratified sampling
• Cluster sampling
• Likert scales
• Reproducibility

 Statistics

• Null hypothesis
• Statistical power
• Probability distribution
• Effect size
• Poisson distribution

Research bias

• Optimism bias
• Cognitive bias
• Implicit bias
• Hawthorne effect
• Anchoring bias
• Explicit bias

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A hypothesis is not just a guess — it should be based on existing theories and knowledge. It also has to be testable, which means you can support or refute it through scientific research methods (such as experiments, observations and statistical analysis of data).

Null and alternative hypotheses are used in statistical hypothesis testing . The null hypothesis of a test always predicts no effect or no relationship between variables, while the alternative hypothesis states your research prediction of an effect or relationship.

Hypothesis testing is a formal procedure for investigating our ideas about the world using statistics. It is used by scientists to test specific predictions, called hypotheses , by calculating how likely it is that a pattern or relationship between variables could have arisen by chance.

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How to Write a Great Hypothesis

Hypothesis Definition, Format, Examples, and Tips

Verywell / Alex Dos Diaz

• The Scientific Method

Hypothesis Format

Falsifiability of a hypothesis.

• Operationalization

Hypothesis Types

Hypotheses examples.

• Collecting Data

A hypothesis is a tentative statement about the relationship between two or more variables. It is a specific, testable prediction about what you expect to happen in a study. It is a preliminary answer to your question that helps guide the research process.

Consider a study designed to examine the relationship between sleep deprivation and test performance. The hypothesis might be: "This study is designed to assess the hypothesis that sleep-deprived people will perform worse on a test than individuals who are not sleep-deprived."

At a Glance

A hypothesis is crucial to scientific research because it offers a clear direction for what the researchers are looking to find. This allows them to design experiments to test their predictions and add to our scientific knowledge about the world. This article explores how a hypothesis is used in psychology research, how to write a good hypothesis, and the different types of hypotheses you might use.

The Hypothesis in the Scientific Method

In the scientific method , whether it involves research in psychology, biology, or some other area, a hypothesis represents what the researchers think will happen in an experiment. The scientific method involves the following steps:

• Forming a question
• Performing background research
• Creating a hypothesis
• Designing an experiment
• Collecting data
• Analyzing the results
• Drawing conclusions
• Communicating the results

The hypothesis is a prediction, but it involves more than a guess. Most of the time, the hypothesis begins with a question which is then explored through background research. At this point, researchers then begin to develop a testable hypothesis.

Unless you are creating an exploratory study, your hypothesis should always explain what you  expect  to happen.

In a study exploring the effects of a particular drug, the hypothesis might be that researchers expect the drug to have some type of effect on the symptoms of a specific illness. In psychology, the hypothesis might focus on how a certain aspect of the environment might influence a particular behavior.

Remember, a hypothesis does not have to be correct. While the hypothesis predicts what the researchers expect to see, the goal of the research is to determine whether this guess is right or wrong. When conducting an experiment, researchers might explore numerous factors to determine which ones might contribute to the ultimate outcome.

In many cases, researchers may find that the results of an experiment  do not  support the original hypothesis. When writing up these results, the researchers might suggest other options that should be explored in future studies.

In many cases, researchers might draw a hypothesis from a specific theory or build on previous research. For example, prior research has shown that stress can impact the immune system. So a researcher might hypothesize: "People with high-stress levels will be more likely to contract a common cold after being exposed to the virus than people who have low-stress levels."

In other instances, researchers might look at commonly held beliefs or folk wisdom. "Birds of a feather flock together" is one example of folk adage that a psychologist might try to investigate. The researcher might pose a specific hypothesis that "People tend to select romantic partners who are similar to them in interests and educational level."

Elements of a Good Hypothesis

So how do you write a good hypothesis? When trying to come up with a hypothesis for your research or experiments, ask yourself the following questions:

• Is your hypothesis based on your research on a topic?
• Can your hypothesis be tested?
• Does your hypothesis include independent and dependent variables?

Before you come up with a specific hypothesis, spend some time doing background research. Once you have completed a literature review, start thinking about potential questions you still have. Pay attention to the discussion section in the  journal articles you read . Many authors will suggest questions that still need to be explored.

How to Formulate a Good Hypothesis

To form a hypothesis, you should take these steps:

• Collect as many observations about a topic or problem as you can.
• Evaluate these observations and look for possible causes of the problem.
• Create a list of possible explanations that you might want to explore.
• After you have developed some possible hypotheses, think of ways that you could confirm or disprove each hypothesis through experimentation. This is known as falsifiability.

In the scientific method ,  falsifiability is an important part of any valid hypothesis. In order to test a claim scientifically, it must be possible that the claim could be proven false.

Students sometimes confuse the idea of falsifiability with the idea that it means that something is false, which is not the case. What falsifiability means is that  if  something was false, then it is possible to demonstrate that it is false.

One of the hallmarks of pseudoscience is that it makes claims that cannot be refuted or proven false.

The Importance of Operational Definitions

A variable is a factor or element that can be changed and manipulated in ways that are observable and measurable. However, the researcher must also define how the variable will be manipulated and measured in the study.

Operational definitions are specific definitions for all relevant factors in a study. This process helps make vague or ambiguous concepts detailed and measurable.

For example, a researcher might operationally define the variable " test anxiety " as the results of a self-report measure of anxiety experienced during an exam. A "study habits" variable might be defined by the amount of studying that actually occurs as measured by time.

These precise descriptions are important because many things can be measured in various ways. Clearly defining these variables and how they are measured helps ensure that other researchers can replicate your results.

Replicability

One of the basic principles of any type of scientific research is that the results must be replicable.

Replication means repeating an experiment in the same way to produce the same results. By clearly detailing the specifics of how the variables were measured and manipulated, other researchers can better understand the results and repeat the study if needed.

Some variables are more difficult than others to define. For example, how would you operationally define a variable such as aggression ? For obvious ethical reasons, researchers cannot create a situation in which a person behaves aggressively toward others.

To measure this variable, the researcher must devise a measurement that assesses aggressive behavior without harming others. The researcher might utilize a simulated task to measure aggressiveness in this situation.

Hypothesis Checklist

• Does your hypothesis focus on something that you can actually test?
• Does your hypothesis include both an independent and dependent variable?
• Can you manipulate the variables?
• Can your hypothesis be tested without violating ethical standards?

The hypothesis you use will depend on what you are investigating and hoping to find. Some of the main types of hypotheses that you might use include:

• Simple hypothesis : This type of hypothesis suggests there is a relationship between one independent variable and one dependent variable.
• Complex hypothesis : This type suggests a relationship between three or more variables, such as two independent and dependent variables.
• Null hypothesis : This hypothesis suggests no relationship exists between two or more variables.
• Alternative hypothesis : This hypothesis states the opposite of the null hypothesis.
• Statistical hypothesis : This hypothesis uses statistical analysis to evaluate a representative population sample and then generalizes the findings to the larger group.
• Logical hypothesis : This hypothesis assumes a relationship between variables without collecting data or evidence.

A hypothesis often follows a basic format of "If {this happens} then {this will happen}." One way to structure your hypothesis is to describe what will happen to the  dependent variable  if you change the  independent variable .

The basic format might be: "If {these changes are made to a certain independent variable}, then we will observe {a change in a specific dependent variable}."

A few examples of simple hypotheses:

• "Students who eat breakfast will perform better on a math exam than students who do not eat breakfast."
• "Students who experience test anxiety before an English exam will get lower scores than students who do not experience test anxiety."​
• "Motorists who talk on the phone while driving will be more likely to make errors on a driving course than those who do not talk on the phone."
• "Children who receive a new reading intervention will have higher reading scores than students who do not receive the intervention."

Examples of a complex hypothesis include:

• "People with high-sugar diets and sedentary activity levels are more likely to develop depression."
• "Younger people who are regularly exposed to green, outdoor areas have better subjective well-being than older adults who have limited exposure to green spaces."

Examples of a null hypothesis include:

• "There is no difference in anxiety levels between people who take St. John's wort supplements and those who do not."
• "There is no difference in scores on a memory recall task between children and adults."
• "There is no difference in aggression levels between children who play first-person shooter games and those who do not."

Examples of an alternative hypothesis:

• "People who take St. John's wort supplements will have less anxiety than those who do not."
• "Adults will perform better on a memory task than children."
• "Children who play first-person shooter games will show higher levels of aggression than children who do not." 

Collecting Data on Your Hypothesis

Once a researcher has formed a testable hypothesis, the next step is to select a research design and start collecting data. The research method depends largely on exactly what they are studying. There are two basic types of research methods: descriptive research and experimental research.

Descriptive Research Methods

Descriptive research such as  case studies ,  naturalistic observations , and surveys are often used when  conducting an experiment is difficult or impossible. These methods are best used to describe different aspects of a behavior or psychological phenomenon.

Once a researcher has collected data using descriptive methods, a  correlational study  can examine how the variables are related. This research method might be used to investigate a hypothesis that is difficult to test experimentally.

Experimental Research Methods

Experimental methods  are used to demonstrate causal relationships between variables. In an experiment, the researcher systematically manipulates a variable of interest (known as the independent variable) and measures the effect on another variable (known as the dependent variable).

Unlike correlational studies, which can only be used to determine if there is a relationship between two variables, experimental methods can be used to determine the actual nature of the relationship—whether changes in one variable actually  cause  another to change.

The hypothesis is a critical part of any scientific exploration. It represents what researchers expect to find in a study or experiment. In situations where the hypothesis is unsupported by the research, the research still has value. Such research helps us better understand how different aspects of the natural world relate to one another. It also helps us develop new hypotheses that can then be tested in the future.

Thompson WH, Skau S. On the scope of scientific hypotheses .  R Soc Open Sci . 2023;10(8):230607. doi:10.1098/rsos.230607

Taran S, Adhikari NKJ, Fan E. Falsifiability in medicine: what clinicians can learn from Karl Popper [published correction appears in Intensive Care Med. 2021 Jun 17;:].  Intensive Care Med . 2021;47(9):1054-1056. doi:10.1007/s00134-021-06432-z

Eyler AA. Research Methods for Public Health . 1st ed. Springer Publishing Company; 2020. doi:10.1891/9780826182067.0004

Nosek BA, Errington TM. What is replication ?  PLoS Biol . 2020;18(3):e3000691. doi:10.1371/journal.pbio.3000691

Aggarwal R, Ranganathan P. Study designs: Part 2 - Descriptive studies .  Perspect Clin Res . 2019;10(1):34-36. doi:10.4103/picr.PICR_154_18

Nevid J. Psychology: Concepts and Applications. Wadworth, 2013.

By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

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The Craft of Writing a Strong Hypothesis

Table of Contents

Writing a hypothesis is one of the essential elements of a scientific research paper. It needs to be to the point, clearly communicating what your research is trying to accomplish. A blurry, drawn-out, or complexly-structured hypothesis can confuse your readers. Or worse, the editor and peer reviewers.

A captivating hypothesis is not too intricate. This blog will take you through the process so that, by the end of it, you have a better idea of how to convey your research paper's intent in just one sentence.

What is a Hypothesis?

The first step in your scientific endeavor, a hypothesis, is a strong, concise statement that forms the basis of your research. It is not the same as a thesis statement , which is a brief summary of your research paper .

The sole purpose of a hypothesis is to predict your paper's findings, data, and conclusion. It comes from a place of curiosity and intuition . When you write a hypothesis, you're essentially making an educated guess based on scientific prejudices and evidence, which is further proven or disproven through the scientific method.

The reason for undertaking research is to observe a specific phenomenon. A hypothesis, therefore, lays out what the said phenomenon is. And it does so through two variables, an independent and dependent variable.

The independent variable is the cause behind the observation, while the dependent variable is the effect of the cause. A good example of this is “mixing red and blue forms purple.” In this hypothesis, mixing red and blue is the independent variable as you're combining the two colors at your own will. The formation of purple is the dependent variable as, in this case, it is conditional to the independent variable.

Different Types of Hypotheses‌

Types of hypotheses

Some would stand by the notion that there are only two types of hypotheses: a Null hypothesis and an Alternative hypothesis. While that may have some truth to it, it would be better to fully distinguish the most common forms as these terms come up so often, which might leave you out of context.

Apart from Null and Alternative, there are Complex, Simple, Directional, Non-Directional, Statistical, and Associative and casual hypotheses. They don't necessarily have to be exclusive, as one hypothesis can tick many boxes, but knowing the distinctions between them will make it easier for you to construct your own.

1. Null hypothesis

A null hypothesis proposes no relationship between two variables. Denoted by H 0 , it is a negative statement like “Attending physiotherapy sessions does not affect athletes' on-field performance.” Here, the author claims physiotherapy sessions have no effect on on-field performances. Even if there is, it's only a coincidence.

2. Alternative hypothesis

Considered to be the opposite of a null hypothesis, an alternative hypothesis is donated as H1 or Ha. It explicitly states that the dependent variable affects the independent variable. A good  alternative hypothesis example is “Attending physiotherapy sessions improves athletes' on-field performance.” or “Water evaporates at 100 °C. ” The alternative hypothesis further branches into directional and non-directional.

• Directional hypothesis: A hypothesis that states the result would be either positive or negative is called directional hypothesis. It accompanies H1 with either the ‘<' or ‘>' sign.
• Non-directional hypothesis: A non-directional hypothesis only claims an effect on the dependent variable. It does not clarify whether the result would be positive or negative. The sign for a non-directional hypothesis is ‘≠.'

3. Simple hypothesis

A simple hypothesis is a statement made to reflect the relation between exactly two variables. One independent and one dependent. Consider the example, “Smoking is a prominent cause of lung cancer." The dependent variable, lung cancer, is dependent on the independent variable, smoking.

4. Complex hypothesis

In contrast to a simple hypothesis, a complex hypothesis implies the relationship between multiple independent and dependent variables. For instance, “Individuals who eat more fruits tend to have higher immunity, lesser cholesterol, and high metabolism.” The independent variable is eating more fruits, while the dependent variables are higher immunity, lesser cholesterol, and high metabolism.

5. Associative and casual hypothesis

Associative and casual hypotheses don't exhibit how many variables there will be. They define the relationship between the variables. In an associative hypothesis, changing any one variable, dependent or independent, affects others. In a casual hypothesis, the independent variable directly affects the dependent.

6. Empirical hypothesis

Also referred to as the working hypothesis, an empirical hypothesis claims a theory's validation via experiments and observation. This way, the statement appears justifiable and different from a wild guess.

Say, the hypothesis is “Women who take iron tablets face a lesser risk of anemia than those who take vitamin B12.” This is an example of an empirical hypothesis where the researcher  the statement after assessing a group of women who take iron tablets and charting the findings.

7. Statistical hypothesis

The point of a statistical hypothesis is to test an already existing hypothesis by studying a population sample. Hypothesis like “44% of the Indian population belong in the age group of 22-27.” leverage evidence to prove or disprove a particular statement.

Characteristics of a Good Hypothesis

Writing a hypothesis is essential as it can make or break your research for you. That includes your chances of getting published in a journal. So when you're designing one, keep an eye out for these pointers:

• A research hypothesis has to be simple yet clear to look justifiable enough.
• It has to be testable — your research would be rendered pointless if too far-fetched into reality or limited by technology.
• It has to be precise about the results —what you are trying to do and achieve through it should come out in your hypothesis.
• A research hypothesis should be self-explanatory, leaving no doubt in the reader's mind.
• If you are developing a relational hypothesis, you need to include the variables and establish an appropriate relationship among them.
• A hypothesis must keep and reflect the scope for further investigations and experiments.

Separating a Hypothesis from a Prediction

Outside of academia, hypothesis and prediction are often used interchangeably. In research writing, this is not only confusing but also incorrect. And although a hypothesis and prediction are guesses at their core, there are many differences between them.

A hypothesis is an educated guess or even a testable prediction validated through research. It aims to analyze the gathered evidence and facts to define a relationship between variables and put forth a logical explanation behind the nature of events.

Predictions are assumptions or expected outcomes made without any backing evidence. They are more fictionally inclined regardless of where they originate from.

For this reason, a hypothesis holds much more weight than a prediction. It sticks to the scientific method rather than pure guesswork. "Planets revolve around the Sun." is an example of a hypothesis as it is previous knowledge and observed trends. Additionally, we can test it through the scientific method.

Whereas "COVID-19 will be eradicated by 2030." is a prediction. Even though it results from past trends, we can't prove or disprove it. So, the only way this gets validated is to wait and watch if COVID-19 cases end by 2030.

Finally, How to Write a Hypothesis

Quick tips on writing a hypothesis

1.  Be clear about your research question

A hypothesis should instantly address the research question or the problem statement. To do so, you need to ask a question. Understand the constraints of your undertaken research topic and then formulate a simple and topic-centric problem. Only after that can you develop a hypothesis and further test for evidence.

2. Carry out a recce

Once you have your research's foundation laid out, it would be best to conduct preliminary research. Go through previous theories, academic papers, data, and experiments before you start curating your research hypothesis. It will give you an idea of your hypothesis's viability or originality.

Making use of references from relevant research papers helps draft a good research hypothesis. SciSpace Discover offers a repository of over 270 million research papers to browse through and gain a deeper understanding of related studies on a particular topic. Additionally, you can use SciSpace Copilot , your AI research assistant, for reading any lengthy research paper and getting a more summarized context of it. A hypothesis can be formed after evaluating many such summarized research papers. Copilot also offers explanations for theories and equations, explains paper in simplified version, allows you to highlight any text in the paper or clip math equations and tables and provides a deeper, clear understanding of what is being said. This can improve the hypothesis by helping you identify potential research gaps.

3. Create a 3-dimensional hypothesis

Variables are an essential part of any reasonable hypothesis. So, identify your independent and dependent variable(s) and form a correlation between them. The ideal way to do this is to write the hypothetical assumption in the ‘if-then' form. If you use this form, make sure that you state the predefined relationship between the variables.

In another way, you can choose to present your hypothesis as a comparison between two variables. Here, you must specify the difference you expect to observe in the results.

4. Write the first draft

Now that everything is in place, it's time to write your hypothesis. For starters, create the first draft. In this version, write what you expect to find from your research.

Clearly separate your independent and dependent variables and the link between them. Don't fixate on syntax at this stage. The goal is to ensure your hypothesis addresses the issue.

5. Proof your hypothesis

After preparing the first draft of your hypothesis, you need to inspect it thoroughly. It should tick all the boxes, like being concise, straightforward, relevant, and accurate. Your final hypothesis has to be well-structured as well.

Research projects are an exciting and crucial part of being a scholar. And once you have your research question, you need a great hypothesis to begin conducting research. Thus, knowing how to write a hypothesis is very important.

Now that you have a firmer grasp on what a good hypothesis constitutes, the different kinds there are, and what process to follow, you will find it much easier to write your hypothesis, which ultimately helps your research.

Now it's easier than ever to streamline your research workflow with SciSpace Discover . Its integrated, comprehensive end-to-end platform for research allows scholars to easily discover, write and publish their research and fosters collaboration.

It includes everything you need, including a repository of over 270 million research papers across disciplines, SEO-optimized summaries and public profiles to show your expertise and experience.

If you found these tips on writing a research hypothesis useful, head over to our blog on Statistical Hypothesis Testing to learn about the top researchers, papers, and institutions in this domain.

Frequently Asked Questions (FAQs)

1. what is the definition of hypothesis.

According to the Oxford dictionary, a hypothesis is defined as “An idea or explanation of something that is based on a few known facts, but that has not yet been proved to be true or correct”.

2. What is an example of hypothesis?

The hypothesis is a statement that proposes a relationship between two or more variables. An example: "If we increase the number of new users who join our platform by 25%, then we will see an increase in revenue."

3. What is an example of null hypothesis?

A null hypothesis is a statement that there is no relationship between two variables. The null hypothesis is written as H0. The null hypothesis states that there is no effect. For example, if you're studying whether or not a particular type of exercise increases strength, your null hypothesis will be "there is no difference in strength between people who exercise and people who don't."

4. What are the types of research?

• Fundamental research

• Applied research

• Qualitative research

• Quantitative research

• Mixed research

• Exploratory research

• Longitudinal research

• Cross-sectional research

• Field research

• Laboratory research

• Fixed research

• Flexible research

• Action research

• Policy research

• Classification research

• Comparative research

• Causal research

• Inductive research

• Deductive research

5. How to write a hypothesis?

• Your hypothesis should be able to predict the relationship and outcome.

• Avoid wordiness by keeping it simple and brief.

• Your hypothesis should contain observable and testable outcomes.

• Your hypothesis should be relevant to the research question.

6. What are the 2 types of hypothesis?

• Null hypotheses are used to test the claim that "there is no difference between two groups of data".

• Alternative hypotheses test the claim that "there is a difference between two data groups".

7. Difference between research question and research hypothesis?

A research question is a broad, open-ended question you will try to answer through your research. A hypothesis is a statement based on prior research or theory that you expect to be true due to your study. Example - Research question: What are the factors that influence the adoption of the new technology? Research hypothesis: There is a positive relationship between age, education and income level with the adoption of the new technology.

8. What is plural for hypothesis?

The plural of hypothesis is hypotheses. Here's an example of how it would be used in a statement, "Numerous well-considered hypotheses are presented in this part, and they are supported by tables and figures that are well-illustrated."

9. What is the red queen hypothesis?

The red queen hypothesis in evolutionary biology states that species must constantly evolve to avoid extinction because if they don't, they will be outcompeted by other species that are evolving. Leigh Van Valen first proposed it in 1973; since then, it has been tested and substantiated many times.

10. Who is known as the father of null hypothesis?

The father of the null hypothesis is Sir Ronald Fisher. He published a paper in 1925 that introduced the concept of null hypothesis testing, and he was also the first to use the term itself.

11. When to reject null hypothesis?

You need to find a significant difference between your two populations to reject the null hypothesis. You can determine that by running statistical tests such as an independent sample t-test or a dependent sample t-test. You should reject the null hypothesis if the p-value is less than 0.05.

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• How to Write a Strong Hypothesis | Guide & Examples

How to Write a Strong Hypothesis | Guide & Examples

Published on 6 May 2022 by Shona McCombes .

A hypothesis is a statement that can be tested by scientific research. If you want to test a relationship between two or more variables, you need to write hypotheses before you start your experiment or data collection.

Table of contents

What is a hypothesis, developing a hypothesis (with example), hypothesis examples, frequently asked questions about writing hypotheses.

A hypothesis states your predictions about what your research will find. It is a tentative answer to your research question that has not yet been tested. For some research projects, you might have to write several hypotheses that address different aspects of your research question.

A hypothesis is not just a guess – it should be based on existing theories and knowledge. It also has to be testable, which means you can support or refute it through scientific research methods (such as experiments, observations, and statistical analysis of data).

Variables in hypotheses

Hypotheses propose a relationship between two or more variables . An independent variable is something the researcher changes or controls. A dependent variable is something the researcher observes and measures.

In this example, the independent variable is exposure to the sun – the assumed cause . The dependent variable is the level of happiness – the assumed effect .

Prevent plagiarism, run a free check.

Step 1: ask a question.

Writing a hypothesis begins with a research question that you want to answer. The question should be focused, specific, and researchable within the constraints of your project.

Step 2: Do some preliminary research

Your initial answer to the question should be based on what is already known about the topic. Look for theories and previous studies to help you form educated assumptions about what your research will find.

At this stage, you might construct a conceptual framework to identify which variables you will study and what you think the relationships are between them. Sometimes, you’ll have to operationalise more complex constructs.

Step 3: Formulate your hypothesis

Now you should have some idea of what you expect to find. Write your initial answer to the question in a clear, concise sentence.

Step 4: Refine your hypothesis

You need to make sure your hypothesis is specific and testable. There are various ways of phrasing a hypothesis, but all the terms you use should have clear definitions, and the hypothesis should contain:

• The relevant variables
• The specific group being studied
• The predicted outcome of the experiment or analysis

Step 5: Phrase your hypothesis in three ways

To identify the variables, you can write a simple prediction in if … then form. The first part of the sentence states the independent variable and the second part states the dependent variable.

In academic research, hypotheses are more commonly phrased in terms of correlations or effects, where you directly state the predicted relationship between variables.

If you are comparing two groups, the hypothesis can state what difference you expect to find between them.

Step 6. Write a null hypothesis

If your research involves statistical hypothesis testing , you will also have to write a null hypothesis. The null hypothesis is the default position that there is no association between the variables. The null hypothesis is written as H 0 , while the alternative hypothesis is H 1 or H a .

Hypothesis testing is a formal procedure for investigating our ideas about the world using statistics. It is used by scientists to test specific predictions, called hypotheses , by calculating how likely it is that a pattern or relationship between variables could have arisen by chance.

A hypothesis is not just a guess. It should be based on existing theories and knowledge. It also has to be testable, which means you can support or refute it through scientific research methods (such as experiments, observations, and statistical analysis of data).

A research hypothesis is your proposed answer to your research question. The research hypothesis usually includes an explanation (‘ x affects y because …’).

A statistical hypothesis, on the other hand, is a mathematical statement about a population parameter. Statistical hypotheses always come in pairs: the null and alternative hypotheses. In a well-designed study , the statistical hypotheses correspond logically to the research hypothesis.

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• National Center for Biotechnology Information - PubMed Central - On the scope of scientific hypotheses
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scientific hypothesis , an idea that proposes a tentative explanation about a phenomenon or a narrow set of phenomena observed in the natural world. The two primary features of a scientific hypothesis are falsifiability and testability, which are reflected in an “If…then” statement summarizing the idea and in the ability to be supported or refuted through observation and experimentation. The notion of the scientific hypothesis as both falsifiable and testable was advanced in the mid-20th century by Austrian-born British philosopher Karl Popper .

The formulation and testing of a hypothesis is part of the scientific method , the approach scientists use when attempting to understand and test ideas about natural phenomena. The generation of a hypothesis frequently is described as a creative process and is based on existing scientific knowledge, intuition , or experience. Therefore, although scientific hypotheses commonly are described as educated guesses, they actually are more informed than a guess. In addition, scientists generally strive to develop simple hypotheses, since these are easier to test relative to hypotheses that involve many different variables and potential outcomes. Such complex hypotheses may be developed as scientific models ( see scientific modeling ).

Depending on the results of scientific evaluation, a hypothesis typically is either rejected as false or accepted as true. However, because a hypothesis inherently is falsifiable, even hypotheses supported by scientific evidence and accepted as true are susceptible to rejection later, when new evidence has become available. In some instances, rather than rejecting a hypothesis because it has been falsified by new evidence, scientists simply adapt the existing idea to accommodate the new information. In this sense a hypothesis is never incorrect but only incomplete.

The investigation of scientific hypotheses is an important component in the development of scientific theory . Hence, hypotheses differ fundamentally from theories; whereas the former is a specific tentative explanation and serves as the main tool by which scientists gather data, the latter is a broad general explanation that incorporates data from many different scientific investigations undertaken to explore hypotheses.

Countless hypotheses have been developed and tested throughout the history of science . Several examples include the idea that living organisms develop from nonliving matter, which formed the basis of spontaneous generation , a hypothesis that ultimately was disproved (first in 1668, with the experiments of Italian physician Francesco Redi , and later in 1859, with the experiments of French chemist and microbiologist Louis Pasteur ); the concept proposed in the late 19th century that microorganisms cause certain diseases (now known as germ theory ); and the notion that oceanic crust forms along submarine mountain zones and spreads laterally away from them ( seafloor spreading hypothesis ).

What Is a Hypothesis? (Science)

If...,Then...

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A hypothesis (plural hypotheses) is a proposed explanation for an observation. The definition depends on the subject.

In science, a hypothesis is part of the scientific method. It is a prediction or explanation that is tested by an experiment. Observations and experiments may disprove a scientific hypothesis, but can never entirely prove one.

In the study of logic, a hypothesis is an if-then proposition, typically written in the form, "If X , then Y ."

In common usage, a hypothesis is simply a proposed explanation or prediction, which may or may not be tested.

Writing a Hypothesis

Most scientific hypotheses are proposed in the if-then format because it's easy to design an experiment to see whether or not a cause and effect relationship exists between the independent variable and the dependent variable . The hypothesis is written as a prediction of the outcome of the experiment.

Null Hypothesis and Alternative Hypothesis

Statistically, it's easier to show there is no relationship between two variables than to support their connection. So, scientists often propose the null hypothesis . The null hypothesis assumes changing the independent variable will have no effect on the dependent variable.

In contrast, the alternative hypothesis suggests changing the independent variable will have an effect on the dependent variable. Designing an experiment to test this hypothesis can be trickier because there are many ways to state an alternative hypothesis.

For example, consider a possible relationship between getting a good night's sleep and getting good grades. The null hypothesis might be stated: "The number of hours of sleep students get is unrelated to their grades" or "There is no correlation between hours of sleep and grades."

An experiment to test this hypothesis might involve collecting data, recording average hours of sleep for each student and grades. If a student who gets eight hours of sleep generally does better than students who get four hours of sleep or 10 hours of sleep, the hypothesis might be rejected.

But the alternative hypothesis is harder to propose and test. The most general statement would be: "The amount of sleep students get affects their grades." The hypothesis might also be stated as "If you get more sleep, your grades will improve" or "Students who get nine hours of sleep have better grades than those who get more or less sleep."

In an experiment, you can collect the same data, but the statistical analysis is less likely to give you a high confidence limit.

Usually, a scientist starts out with the null hypothesis. From there, it may be possible to propose and test an alternative hypothesis, to narrow down the relationship between the variables.

Example of a Hypothesis

Examples of a hypothesis include:

• If you drop a rock and a feather, (then) they will fall at the same rate.
• Plants need sunlight in order to live. (if sunlight, then life)
• Eating sugar gives you energy. (if sugar, then energy)
• White, Jay D.  Research in Public Administration . Conn., 1998.
• Schick, Theodore, and Lewis Vaughn.  How to Think about Weird Things: Critical Thinking for a New Age . McGraw-Hill Higher Education, 2002.
• Scientific Method Flow Chart
• Six Steps of the Scientific Method
• What Are the Elements of a Good Hypothesis?
• What Are Examples of a Hypothesis?
• What Is a Testable Hypothesis?
• Null Hypothesis Examples
• Scientific Hypothesis Examples
• Scientific Variable
• Scientific Method Vocabulary Terms
• Understanding Simple vs Controlled Experiments
• What Is a Controlled Experiment?
• What Is an Experimental Constant?
• What Is the Difference Between a Control Variable and Control Group?
• DRY MIX Experiment Variables Acronym
• Random Error vs. Systematic Error
• The Role of a Controlled Variable in an Experiment

How The Moon Was Formed: The Giant Impact Hypothesis

We don’t know all the details yet, but we have a good idea of the true origins of our only natural satellite.

Gear-obsessed editors choose every product we review. We may earn commission if you buy from a link. Why Trust Us?

• Lunar research began in earnest when Apollo astronauts brought moon rocks back to Earth in 1969.
• We are learning more about the moon than ever, as techniques for analyzing the chemical composition of old and new lunar samples continue to advance.

As one of Earth’s most familiar sights in the sky, the moon has inspired billions of people to gaze upward in wonder. Early in humanity’s history, we constructed myths about this silvery orb, and later, we pursued a space race to explore it on foot. Always, there was a standout mystery: how did the moon form and find a home orbiting our blue planet?

🌒 You love the cosmos. So do we. Let’s nerd out over it together.

Apollo astronauts kick-started scientific research to answer this question when they returned from the moon in 1969 with about 48 pounds of lunar rock and dust . By measuring the age of the rocks, scientists learned that the moon formed about 4.5 billion years ago, amidst the chaotic early years of our Solar System’s own formation. Today’s tools and techniques can analyze the chemistry of lunar material in ways that were impossible just 50 years ago, revealing more detail than ever before about the story of our moon.

☄️ The Giant Impact Hypothesis Remains the Best Explanation

The generally accepted model of the moon’s creation assumes that a massive object, dubbed Theia, crashed directly into Earth 4.51 billion years ago, when our planet was still busy growing to its current size and forming its core. The resulting impact vaporized part of young Earth’s mantle , tossing rocks and gasses outward. After some time, the ejected matter (a combination of Earth material and Theia material) began orbiting our planet. The clumps of gas, dust, and rock collided and stuck together.

After just a few thousand years—recent models reveal this surprisingly short period—they coalesced into a spherical shape that continued orbiting Earth. The early moon rock was so hot that it was an entirely molten world, and it took 150 to 200 million years to cool and crystallize into its familiar, gray, rocky exterior. Theia was the catalyst for our planet’s formation, too, as it helped push heavier elements like nickel and iron toward the core.

“Over the last 50 years, the Giant Impact Hypothesis has become the favored explanation, which I believe is the best approximation of what likely happened given the geochemical data we’ve been able to collect,” geochemist Erick Cano of the University of New Mexico in Albuquerque tells Popular Mechanics in an email.

While the Giant Impact Hypothesis is generally accepted, we still have many mysteries about the moon’s history.

The biggest challenge to planetary scientists trying to reconstruct the story of the moon is that their clues come from “very processed” rocks, Anthony Gargano, another geochemist at the University of New Mexico, tells Popular Mechanics . The moon has undergone billions of years of changes since its inception. Our satellite experienced vaporization, magma, and crystallization, all of which transformed the rocks.

🌝 Studying the Moon’s Chemical Composition for Clues

Luckily, measurement technologies used to study planet formation are rapidly improving. Scientists are able to measure chemical compositions in ways they were not able to in the Apollo days. For example, we can now examine a slice of moon rock under an electron microscope or even study a grain of moon dust using atom probe tomography (APT). This technique distinguishes atomic-level differences in materials.

Measurement of stable isotopes is also particularly informative. Oxygen, for example, comes in light and heavy varieties, with the “heavy” version having two more neutrons in its atomic nucleus than the “light” version. The amounts of each isotope present on the lunar samples reveals more about processes that shaped the environment on the moon.

Early studies calculated the average value of oxygen isotopes in lunar rock found at several different regions of the moon, Cano says. Because those studies took an average of the measurements, scientists today know that the results were misleading; the measurements indicated that the moon’s chemical composition was virtually identical to Earth’s, but that evidence goes against the idea of a moon containing material from a secondary body colliding with Earth. One explanation to justify the identical chemical composition is that meteor impacts delivered the oxygen.

Thanks to a different approach that examined the same samples, a study in March 2020 cleared up the confusion. The evidence , which Cano and other researchers presented in Nature Geoscience , examined each sample separately with high-precision measurement tools, finding distinct characteristics in each one. Scientists concluded that the moon appears to have different oxygen isotope compositions from our planet.

This data, found in samples from deep inside the lunar mantle, 30 miles beneath the surface, supports a giant impact origin story. Furthermore, this reveals more about the mysterious Theia. “Our findings imply that the distinct oxygen isotope compositions of Theia and Earth were not completely homogenized by the moon-forming impact, thus providing quantitative evidence that Theia could have formed farther from the sun than did Earth,” the researchers note in their paper.

Another NASA-led study also reveals more about the geochemistry of the giant impact. Planetary scientists know that the element chlorine vaporizes at low temperatures, so they used chlorine to track planet formation. Earth has an abundance of light chlorine. In contrast, the moon rocks scientists examined contained more of the heavy chlorine isotope. A sound explanation is that as Earth and the moon reformed after the impact, the larger-bodied Earth drew away most of the light chlorine. “The chlorine loss from the moon likely happened during a high-energy and heat event, which points to the Giant Impact theory,” Gargano, one of the lead researchers, says in a NASA press release. The team’s work was published in September 2020 in the Proceedings of the National Academy of Sciences .

🧪 Where Did the Moon’s Carbon Come From?

Recently, scientists at several Japanese universities and the Japan Aerospace Exploration Agency found a surprise on the moon in the form of carbon ion emissions from the moon’s surface. They used data collected during the KAGUYA mission, Japan’s second mission to explore the moon from orbit. Launched in 2007, it created the most detailed topographical model we have of our rocky neighbor with the aid of 15 different instruments. Investigations of the data it collected over almost two years about the moon’s geology are challenging previous research on lunar samples.

Scientists previously believed there was not much carbon at all on the moon, even though this volatile element normally influences the formation and evolution of planetary bodies. Yet, the estimated carbon emissions KAGUYA found on the moon’s surface were far greater in quantity than expected, researchers reported in Science Advances in May 2020. Instruments showed that carbon ions were distributed across almost the entire lunar surface. Therefore, it must be indigenous to the moon, researchers concluded.

This evidence means the carbon must have been embedded in the moon during its formation or soon afterward. The study also notes that the moon’s basaltic plains emit far more carbon ion emissions than the highlands. It’s evidence for carbon existing on the moon for billions of years, rather than entering later from outside sources such as solar wind or meteorites. Instruments were detecting carbon emissions at a rate of about 5.0 × 10⁴ per square centimeter per second, which is far greater than solar wind and micrometeoroids could supply, according to the study.

The Story of the Moon Is Still Taking Shape

In the same year, researchers in Germany uncovered another compelling piece of the story, evidence that the moon took shape just a few thousand years after the impact. The study , published in July 2020 in the journal Science Advances , found that ejected matter from Thiea and Earth condensed into a magma ocean 600 miles deep. It took 150 to 200 million years for that liquid rock to fully crystallize, according to the computer simulation models researchers used in this study. Previous estimates said the moon took just 35 million years to cool into a solid crust.

Russia’s Luna missions have collected lunar material as well. China’s recent Chang’e-5 probe collected samples from the dark side of the moon. The area the Apollo rocks came from is only a small region of the moon, so it’s like trying to put together a giant puzzle when you have only a few pieces, Cano says.

Putting together data from all of these experiments and missions will be the key to painting a clearer picture of the moon’s experiences since its birth 4.5 billion years ago. So far, we don’t have access to data from some of those countries, such as China.

“Even with just the current samples and data we have available, scientists are still coming up with new ideas regarding the details of lunar formation,” Cano says. Still, an overwhelming amount of chemical evidence exists to support the Giant Impact Hypothesis, Gargano says. At this point, the work is all about filling in the details.

Cano agrees. “In my opinion, the current data we have is enough to make a reasonable hypothesis about the moon’s origin. However, in order to determine the specific details of its formation, we would likely need to return to the lunar surface and collect more samples and do a more in-depth geological study,” Cano says.

We won’t have to wait long for another batch of lunar samples to inform our lingering questions about how the moon came to be. NASA will launch a human return to the moon by 2024 with the Artemis mission .

Before joining Popular Mechanics , Manasee Wagh worked as a newspaper reporter, a science journalist, a tech writer, and a computer engineer. She’s always looking for ways to combine the three greatest joys in her life: science, travel, and food.

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• Published: 09 January 2017

A multiple-impact origin for the Moon

• Raluca Rufu 1 ,
• Oded Aharonson 1 &
• Hagai B. Perets   ORCID: orcid.org/0000-0002-5004-199X 2  

Nature Geoscience volume  10 ,  pages 89–94 ( 2017 ) Cite this article

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The hypothesis of lunar origin by a single giant impact can explain some aspects of the Earth–Moon system. However, it is difficult to reconcile giant-impact models with the compositional similarity of the Earth and Moon without violating angular momentum constraints. Furthermore, successful giant-impact scenarios require very specific conditions such that they have a low probability of occurring. Here we present numerical simulations suggesting that the Moon could instead be the product of a succession of a variety of smaller collisions. In this scenario, each collision forms a debris disk around the proto-Earth that then accretes to form a moonlet. The moonlets tidally advance outward, and may coalesce to form the Moon. We find that sub-lunar moonlets are a common result of impacts expected onto the proto-Earth in the early Solar System and find that the planetary rotation is limited by impact angular momentum drain. We conclude that, assuming efficient merger of moonlets, a multiple-impact scenario can account for the formation of the Earth–Moon system with its present properties.

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Acknowledgements

We thank S. Stewart and R. Citron for providing guidance on the computational code, as well as A. Mastrobuono-Battisti for providing the data used for the Monte Carlo simulations. This project was supported by the Minerva Center for Life Under Extreme Planetary Conditions as well as by the I-CORE Program of the PBC and ISF (Center No. 1829/12). R.R. is grateful to the Israel Ministry of Science, Technology and Space for their Shulamit Aloni fellowship. H.B.P. also acknowledges support from the Israel-US bi-national science foundation, BSF grant number 2012384, and the European union career integration grant ‘GRAND’.

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Raluca Rufu & Oded Aharonson

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R.R. performed the SPH simulations and their analysis with guidance by O.A. H.B.P. suggested the multiple-impact idea. All authors contributed to discussions, interpretations and writing.

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How Was the Solar System Formed? – The Nebular Hypothesis

Since time immemorial, humans have been searching for the answer of how the Universe came to be. However, it has only been within the past few centuries, with the Scientific Revolution, that the predominant theories have been empirical in nature. It was during this time, from the 16th to 18th centuries, that astronomers and physicists began to formulate evidence-based explanations of how our Sun, the planets, and the Universe began.

When it comes to the formation of our Solar System, the most widely accepted view is known as the Nebular Hypothesis . In essence, this theory states that the Sun, the planets, and all other objects in the Solar System formed from nebulous material billions of years ago. Originally proposed to explain the origin of the Solar System, this theory has gone on to become a widely accepted view of how all star systems came to be.

Nebular Hypothesis:

According to this theory, the Sun and all the planets of our Solar System began as a giant cloud of molecular gas and dust. Then, about 4.57 billion years ago, something happened that caused the cloud to collapse. This could have been the result of a passing star, or shock waves from a supernova, but the end result was a gravitational collapse at the center of the cloud.

From this collapse, pockets of dust and gas began to collect into denser regions. As the denser regions pulled in more and more matter, conservation of momentum caused it to begin rotating, while increasing pressure caused it to heat up. Most of the material ended up in a ball at the center while the rest of the matter flattened out into disk that circled around it. While the ball at the center formed the Sun, the rest of the material would form into the protoplanetary disc .

The planets formed by accretion from this disc, in which dust and gas gravitated together and coalesced to form ever larger bodies. Due to their higher boiling points, only metals and silicates could exist in solid form closer to the Sun, and these would eventually form the terrestrial planets of Mercury , Venus , Earth , and Mars . Because metallic elements only comprised a very small fraction of the solar nebula, the terrestrial planets could not grow very large.

In contrast, the giant planets ( Jupiter , Saturn , Uranus , and Neptune ) formed beyond the point between the orbits of Mars and Jupiter where material is cool enough for volatile icy compounds to remain solid (i.e. the Frost Line ). The ices that formed these planets were more plentiful than the metals and silicates that formed the terrestrial inner planets, allowing them to grow massive enough to capture large atmospheres of hydrogen and helium. Leftover debris that never became planets congregated in regions such as the Asteroid Belt , Kuiper Belt , and Oort Cloud .

Within 50 million years, the pressure and density of hydrogen in the center of the protostar became great enough for it to begin thermonuclear fusion. The temperature, reaction rate, pressure, and density increased until hydrostatic equilibrium was achieved. At this point, the Sun became a main-sequence star. Solar wind from the Sun created the heliosphere and swept away the remaining gas and dust from the protoplanetary disc into interstellar space, ending the planetary formation process.

History of the Nebular Hypothesis:

The idea that the Solar System originated from a nebula was first proposed in 1734 by Swedish scientist and theologian Emanual Swedenborg. Immanuel Kant, who was familiar with Swedenborg’s work, developed the theory further and published it in his Universal Natural History and Theory of the Heavens  (1755). In this treatise, he argued that gaseous clouds (nebulae) slowly rotate, gradually collapsing and flattening due to gravity and forming stars and planets.

A similar but smaller and more detailed model was proposed by Pierre-Simon Laplace in his treatise Exposition du system du monde (Exposition of the system of the world), which he released in 1796. Laplace theorized that the Sun originally had an extended hot atmosphere throughout the Solar System, and that this “protostar cloud” cooled and contracted. As the cloud spun more rapidly, it threw off material that eventually condensed to form the planets.

The Laplacian nebular model was widely accepted during the 19th century, but it had some rather pronounced difficulties. The main issue was angular momentum distribution between the Sun and planets, which the nebular model could not explain. In addition, Scottish scientist James Clerk Maxwell (1831 – 1879) asserted that different rotational velocities between the inner and outer parts of a ring could not allow for condensation of material.

It was also rejected by astronomer Sir David Brewster (1781 – 1868), who stated that:

“those who believe in the Nebular Theory consider it as certain that our Earth derived its solid matter and its atmosphere from a ring thrown from the Solar atmosphere, which afterwards contracted into a solid terraqueous sphere, from which the Moon was thrown off by the same process… [Under such a view] the Moon must necessarily have carried off water and air from the watery and aerial parts of the Earth and must have an atmosphere.”

By the early 20th century, the Laplacian model had fallen out of favor, prompting scientists to seek out new theories. However, it was not until the 1970s that the modern and most widely accepted variant of the nebular hypothesis – the solar nebular disk model (SNDM) – emerged. Credit for this goes to Soviet astronomer Victor Safronov and his book Evolution of the protoplanetary cloud and formation of the Earth and the planets (1972) . In this book, almost all major problems of the planetary formation process were formulated and many were solved.

For example, the SNDM model has been successful in explaining the appearance of accretion discs around young stellar objects. Various simulations have also demonstrated that the accretion of material in these discs leads to the formation of a few Earth-sized bodies. Thus the origin of terrestrial planets is now considered to be an almost solved problem.

While originally applied only to the Solar System, the SNDM was subsequently thought by theorists to be at work throughout the Universe, and has been used to explain the formation of many of the exoplanets that have been discovered throughout our galaxy.

Although the nebular theory is widely accepted, there are still problems with it that astronomers have not been able to resolve. For example, there is the problem of tilted axes. According to the nebular theory, all planets around a star should be tilted the same way relative to the ecliptic. But as we have learned, the inner planets and outer planets have radically different axial tilts.

Whereas the inner planets range from almost 0 degree tilt, others (like Earth and Mars) are tilted significantly (23.4° and 25°, respectively), outer planets have tilts that range from Jupiter’s minor tilt of 3.13°, to Saturn and Neptune’s more pronounced tilts (26.73° and 28.32°), to Uranus’ extreme tilt of 97.77°, in which its poles are consistently facing towards the Sun.

Also, the study of extrasolar planets have allowed scientists to notice irregularities that cast doubt on the nebular hypothesis. Some of these irregularities have to do with the existence of “hot Jupiters” that orbit closely to their stars with periods of just a few days. Astronomers have adjusted the nebular hypothesis to account for some of these problems, but have yet to address all outlying questions.

Alas, it seems that it questions that have to do with origins that are the toughest to answer. Just when we think we have a satisfactory explanation, there remain those troublesome issues it just can’t account for. However, between our current models of star and planet formation, and the birth of our Universe, we have come a long way. As we learn more about neighboring star systems and explore more of the cosmos, our models are likely to mature further.

We have written many articles about the Solar System here at Universe Today. Here’s The Solar System , Did our Solar System Start with a Little Bang? , and What was Here Before the Solar System?

For more information, be sure to check out the origin of the Solar System and how the Sun and planets formed .

Astronomy Cast also has an episode on the subject – Episode 12: Where do Baby Stars Come From?

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5 Replies to “How Was the Solar System Formed? – The Nebular Hypothesis”

So… the transition from the geocentric view and eternal state the way things are evolved with appreciation of dinosaurs and plate tectonics too… and then refining the nebular idea… the Nice model… the Grand Tack model… alittle more? Now maybe the Grand Tack with the assumption of mantle breaking impacts in the early days – those first 10 millions years were heady times!

And the whole idea of “solar siblings” has been busy the last few years…

Nice overview, and I learned a lot. However, there are some salient points that I think I have picked up earlier:

“something happened that caused the cloud to collapse. This could have been the result of a passing star, or shock waves from a supernova, but the end result was a gravitational collapse at the center of the cloud.”

The study of star forming molecular clouds shows that same early, large stars form that way. In the most elaborate model which makes Earth isotope measurements easiest to predict, by free coupling the processes, the 1st generation of super massive stars would go supernova in 1-10 million years.

That blows a 1st geeration of large bubbles with massive, compressed shells that are seeded with supernova elements, as we see Earth started out with. The shells would lead to a more frequent 2nd generation of massive stars with a lifetime of 10-100 million years or so. These stars have powerful solar winds.

That blows a 2nd generation of large bubbles with massive, compressed shells, The shells would lead to a 3d generation of ~ 500 – 1000 stars of Sun size or less. In the case of the Sun the resulting mass was not enough to lead to a closed star cluster as we can see circling the Milky Way, but an open star cluster where the stars would mix with other stars over the ~ 20 orbits we have done around the MW.

“The ices that formed these planets were more plentiful”.

The astronomy course I attended looked at the core collapse model of large planets. (ASs well as the direct collapse scenario.) The core grew large rapidly and triggered gas collapse onto the planet from the disk, a large factor being the stickiness of ices at the grain stage. The terrestrial planets grow by slower accretion, and the material may have started to be cleared from the disk. by star infall or radiation pressure flow outwards, before they are finished.

An interesting problem for terrestrial planets is the “meter size problem” (IIRC the name). It was considered hard to grow grains above a cm, and when they grow they rapidly brake and fall onto the star.

Now scientists have come up with grain collapse scenarios, where grains start to follow each other for reasons of gravity and viscous properties of the disk, I think. All sorts of bodies up to protoplanets can be grown quickly and, when over the problematic size, will start to clear the disk rather than being braked by it.

“But as we have learned, the inner planets and outer planets have radically different axial tilts.”

Jupiter can be considered a clue, too massive to tilt by outside forces. The general explanation tend to be the accretion process, where the tilt would be randomized. (Venus may be an exception, since some claim it is becoming tidally locked to the Sun – Mercury is instead locked in a 3:2 resonance – and it is in fact now retrograde with a putative near axis lock.) Possible Mercury bit at least Earth and Mars (and Moon) show late great impacts.

A recent paper show that terrestrial planets would suffer impacts on the great impact scale, between 1 to 8 as norm with an average of 3. These would not be able to clear out an Earth mass atmosphere or ocean, so if Earth suffered one such impact after having volatiles delivered by late accretion/early bombardment, the Moon could result.

Comments are closed.

How was the moon formed?

Scientists are still unsure as to how the moon formed, but here are three of their best bets.

Giant impact hypothesis

Co-formation theory, capture theory, additional resources, bibliography.

The moon formed a hundred million years after the creation of the solar system . This has left scientists wondering what was the cause of our planet's satellite to birth if it didn't come from the events that formation of the planets. Here are just three of the most plausible explanations. 

The prevailing theory supported by the scientific community, the giant impact hypothesis suggests that the moon formed when an object smashed into early  Earth . Like the other planets, Earth formed from the leftover cloud of dust and gas orbiting the young sun. The early  solar system  was a violent place, and a number of bodies were created that never made it to full planetary status. One of these could have  crashed into Earth  not long after the young planet was created.

Known as Theia, the Mars-sized body collided with Earth, throwing vaporized chunks of the young planet's crust into space. Gravity bound the ejected particles together, creating a moon that is the  largest  in the solar system in relation to its host planet. This sort of formation would explain why the moon is made up predominantly of lighter elements, making it less dense than Earth — the material that formed it came from the crust, while leaving the planet's rocky core untouched. As the material  drew together  around what was left of Theia's core, it would have centered near Earth's ecliptic plane, the path the sun travels through the sky, which is  where the moon orbits today .

According to NASA , "When the young Earth and this rogue body collided, the energy involved was 100 million times larger than the much later event believed to have wiped out the dinosaurs."

Although this is the most popular theory, it is not without its challenges. Most models suggest that more than 60%of the moon should be made up of the material from Theia. But rock samples from the Apollo missions suggest otherwise.

"In terms of composition, the Earth and moon are almost twins, their compositions differing by at most few parts in a million," Alessandra Mastrobuono-Battisti, an astrophysicist at the Israel Institute of Technology in Haifa, told Space.com. "This contradiction has cast a long shadow on the giant-impact model."

In 2020 research published in Nature Geoscience , offered an explanation as to why the moon and Earth have such similar composition. Having studied the isotopes of oxygen in the moon rocks brought to Earth from Apollo astronauts, researchers discovered that there is a small difference when compared with Earth rocks. The samples collected from the deep lunar mantle (the layer below the crust) were much heavier than those found on Earth and "have isotopic compositions that are most representative of the proto-lunar impactor ‘Theia’", the study authors wrote. 

Back in 2017, Israeli researchers proposed an alternative impact theory which suggests that a rain of small debris fell on Earth to create the moon.

"The multiple-impact scenario is a more natural way of explaining the formation of the moon," Raluca Rufu, a researcher at the Weizmann Institute of Science in Israel and lead author of the study, told Space.com. "In the early stages of the solar system, impacts were very abundant; therefore, it is more natural that several common impactors formed the moon, rather than one special one.

Moons can also form at the same time as their parent planet. Under such an explanation, gravity would have caused material in the early solar system to draw together at the same time as gravity bound particles together to form Earth. Such a moon would have a very similar composition to the planet, and would explain the moon's present location. However, although Earth and the moon share much of the same material, the moon is much less dense than our planet, which would likely not be the case if both started with the same heavy elements at their core.

– Does the moon rotate?

– Atmosphere of the moon

– How Far is the Moon?

– Every mission to the moon

In 2012, researcher Robin Canup, of the Southwest Research Institute in Texas, proposed that Earth and the moon formed at the same time when two massive objects five times the size of Mars crashed into each other.

"After colliding, the two similar-sized bodies then re-collided, forming an early Earth surrounded by a disk of material that combined to form the moon," NASA said . "The re-collision and subsequent merger left the two bodies with the similar chemical compositions seen today.

Perhaps Earth's gravity snagged a passing body, as happened with other moons in the solar system, such as the Martian moons of Phobos and Deimos . Under the capture theory, a rocky body formed elsewhere in the solar system could have been drawn into orbit around Earth. The capture theory would explain the differences in the composition of Earth and its moon. However, such orbiters are often oddly shaped, rather than being spherical bodies like the moon. Their paths don't tend to line up with the ecliptic of their parent planet, also unlike the moon.

Although the co-formation theory and the capture theory both explain some elements of the existence of the moon, they leave many questions unanswered. At present, the giant impact hypothesis seems to cover many of these questions, making it the best model to fit the scientific evidence for how the moon was created.

For more on the giant-impact hypothesis, read "The Big Splat, or How Our Moon Came to be: A Violent Natural History"," by Dana Mackenzie. To learn more about the solar system, check out " Our Solar System: An Exploration of Planets, Moons, Asteroids, and Other Mysteries of Space " by Lisa Reichley. 

Erick J. Cano et al, "Distinct oxygen isotope compositions of the Earth and Moon", Nature Geoscience, Volume 13, March 2020, https://doi.org/10.1038/s41561-020-0550-0 

Raluca Rufu, "A multiple-impact origin for the Moon", Nature Geoscience, Volume 10, January 2017, https://doi.org/10.1038/ngeo2866

Edward Belbruno et al, " Where Did the Moon Come From? ", The Astronomical Journal, Volume 129, March 2005.

Thomas S. Kruijer and Gregory Archer, "No 182W evidence for early Moon formation", Nature Geoscience, Volume 14, October 2021, https://doi.org/ 10.1038/s41561-021-00820-2

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What Is a Hypothesis and How Do I Write One?

General Education

Think about something strange and unexplainable in your life. Maybe you get a headache right before it rains, or maybe you think your favorite sports team wins when you wear a certain color. If you wanted to see whether these are just coincidences or scientific fact, you would form a hypothesis, then create an experiment to see whether that hypothesis is true or not.

But what is a hypothesis, anyway? If you’re not sure about what a hypothesis is--or how to test for one!--you’re in the right place. This article will teach you everything you need to know about hypotheses, including: 

• Defining the term “hypothesis” 
• Providing hypothesis examples 
• Giving you tips for how to write your own hypothesis

So let’s get started!

What Is a Hypothesis?

Merriam Webster defines a hypothesis as “an assumption or concession made for the sake of argument.” In other words, a hypothesis is an educated guess . Scientists make a reasonable assumption--or a hypothesis--then design an experiment to test whether it’s true or not. Keep in mind that in science, a hypothesis should be testable. You have to be able to design an experiment that tests your hypothesis in order for it to be valid. 

As you could assume from that statement, it’s easy to make a bad hypothesis. But when you’re holding an experiment, it’s even more important that your guesses be good...after all, you’re spending time (and maybe money!) to figure out more about your observation. That’s why we refer to a hypothesis as an educated guess--good hypotheses are based on existing data and research to make them as sound as possible.

Hypotheses are one part of what’s called the scientific method .  Every (good) experiment or study is based in the scientific method. The scientific method gives order and structure to experiments and ensures that interference from scientists or outside influences does not skew the results. It’s important that you understand the concepts of the scientific method before holding your own experiment. Though it may vary among scientists, the scientific method is generally made up of six steps (in order):

• Observation
• Asking questions
• Forming a hypothesis
• Analyze the data
• Communicate your results

You’ll notice that the hypothesis comes pretty early on when conducting an experiment. That’s because experiments work best when they’re trying to answer one specific question. And you can’t conduct an experiment until you know what you’re trying to prove!

Independent and Dependent Variables 

After doing your research, you’re ready for another important step in forming your hypothesis: identifying variables. Variables are basically any factor that could influence the outcome of your experiment . Variables have to be measurable and related to the topic being studied.

There are two types of variables:  independent variables and dependent variables. I ndependent variables remain constant . For example, age is an independent variable; it will stay the same, and researchers can look at different ages to see if it has an effect on the dependent variable. 

Speaking of dependent variables... dependent variables are subject to the influence of the independent variable , meaning that they are not constant. Let’s say you want to test whether a person’s age affects how much sleep they need. In that case, the independent variable is age (like we mentioned above), and the dependent variable is how much sleep a person gets. 

Variables will be crucial in writing your hypothesis. You need to be able to identify which variable is which, as both the independent and dependent variables will be written into your hypothesis. For instance, in a study about exercise, the independent variable might be the speed at which the respondents walk for thirty minutes, and the dependent variable would be their heart rate. In your study and in your hypothesis, you’re trying to understand the relationship between the two variables.

Elements of a Good Hypothesis

The best hypotheses start by asking the right questions . For instance, if you’ve observed that the grass is greener when it rains twice a week, you could ask what kind of grass it is, what elevation it’s at, and if the grass across the street responds to rain in the same way. Any of these questions could become the backbone of experiments to test why the grass gets greener when it rains fairly frequently.

As you’re asking more questions about your first observation, make sure you’re also making more observations . If it doesn’t rain for two weeks and the grass still looks green, that’s an important observation that could influence your hypothesis. You'll continue observing all throughout your experiment, but until the hypothesis is finalized, every observation should be noted.

Finally, you should consult secondary research before writing your hypothesis . Secondary research is comprised of results found and published by other people. You can usually find this information online or at your library. Additionally, m ake sure the research you find is credible and related to your topic. If you’re studying the correlation between rain and grass growth, it would help you to research rain patterns over the past twenty years for your county, published by a local agricultural association. You should also research the types of grass common in your area, the type of grass in your lawn, and whether anyone else has conducted experiments about your hypothesis. Also be sure you’re checking the quality of your research . Research done by a middle school student about what minerals can be found in rainwater would be less useful than an article published by a local university.

Writing Your Hypothesis

Once you’ve considered all of the factors above, you’re ready to start writing your hypothesis. Hypotheses usually take a certain form when they’re written out in a research report.

When you boil down your hypothesis statement, you are writing down your best guess and not the question at hand . This means that your statement should be written as if it is fact already, even though you are simply testing it.

The reason for this is that, after you have completed your study, you'll either accept or reject your if-then or your null hypothesis. All hypothesis testing examples should be measurable and able to be confirmed or denied. You cannot confirm a question, only a statement! 

In fact, you come up with hypothesis examples all the time! For instance, when you guess on the outcome of a basketball game, you don’t say, “Will the Miami Heat beat the Boston Celtics?” but instead, “I think the Miami Heat will beat the Boston Celtics.” You state it as if it is already true, even if it turns out you’re wrong. You do the same thing when writing your hypothesis.

Additionally, keep in mind that hypotheses can range from very specific to very broad.  These hypotheses can be specific, but if your hypothesis testing examples involve a broad range of causes and effects, your hypothesis can also be broad.  

The Two Types of Hypotheses

Now that you understand what goes into a hypothesis, it’s time to look more closely at the two most common types of hypothesis: the if-then hypothesis and the null hypothesis.

#1: If-Then Hypotheses

First of all, if-then hypotheses typically follow this formula:

If ____ happens, then ____ will happen.

The goal of this type of hypothesis is to test the causal relationship between the independent and dependent variable. It’s fairly simple, and each hypothesis can vary in how detailed it can be. We create if-then hypotheses all the time with our daily predictions. Here are some examples of hypotheses that use an if-then structure from daily life: 

• If I get enough sleep, I’ll be able to get more work done tomorrow.
• If the bus is on time, I can make it to my friend’s birthday party. 
• If I study every night this week, I’ll get a better grade on my exam. 

In each of these situations, you’re making a guess on how an independent variable (sleep, time, or studying) will affect a dependent variable (the amount of work you can do, making it to a party on time, or getting better grades). 

You may still be asking, “What is an example of a hypothesis used in scientific research?” Take one of the hypothesis examples from a real-world study on whether using technology before bed affects children’s sleep patterns. The hypothesis read s:

“We hypothesized that increased hours of tablet- and phone-based screen time at bedtime would be inversely correlated with sleep quality and child attention.”

It might not look like it, but this is an if-then statement. The researchers basically said, “If children have more screen usage at bedtime, then their quality of sleep and attention will be worse.” The sleep quality and attention are the dependent variables and the screen usage is the independent variable. (Usually, the independent variable comes after the “if” and the dependent variable comes after the “then,” as it is the independent variable that affects the dependent variable.) This is an excellent example of how flexible hypothesis statements can be, as long as the general idea of “if-then” and the independent and dependent variables are present.

#2: Null Hypotheses

Your if-then hypothesis is not the only one needed to complete a successful experiment, however. You also need a null hypothesis to test it against. In its most basic form, the null hypothesis is the opposite of your if-then hypothesis . When you write your null hypothesis, you are writing a hypothesis that suggests that your guess is not true, and that the independent and dependent variables have no relationship .

One null hypothesis for the cell phone and sleep study from the last section might say: 

“If children have more screen usage at bedtime, their quality of sleep and attention will not be worse.” 

In this case, this is a null hypothesis because it’s asking the opposite of the original thesis! 

Conversely, if your if-then hypothesis suggests that your two variables have no relationship, then your null hypothesis would suggest that there is one. So, pretend that there is a study that is asking the question, “Does the amount of followers on Instagram influence how long people spend on the app?” The independent variable is the amount of followers, and the dependent variable is the time spent. But if you, as the researcher, don’t think there is a relationship between the number of followers and time spent, you might write an if-then hypothesis that reads:

“If people have many followers on Instagram, they will not spend more time on the app than people who have less.”

In this case, the if-then suggests there isn’t a relationship between the variables. In that case, one of the null hypothesis examples might say:

“If people have many followers on Instagram, they will spend more time on the app than people who have less.”

You then test both the if-then and the null hypothesis to gauge if there is a relationship between the variables, and if so, how much of a relationship. 

4 Tips to Write the Best Hypothesis

If you’re going to take the time to hold an experiment, whether in school or by yourself, you’re also going to want to take the time to make sure your hypothesis is a good one. The best hypotheses have four major elements in common: plausibility, defined concepts, observability, and general explanation.

#1: Plausibility

At first glance, this quality of a hypothesis might seem obvious. When your hypothesis is plausible, that means it’s possible given what we know about science and general common sense. However, improbable hypotheses are more common than you might think. 

Imagine you’re studying weight gain and television watching habits. If you hypothesize that people who watch more than  twenty hours of television a week will gain two hundred pounds or more over the course of a year, this might be improbable (though it’s potentially possible). Consequently, c ommon sense can tell us the results of the study before the study even begins.

Improbable hypotheses generally go against  science, as well. Take this hypothesis example: 

“If a person smokes one cigarette a day, then they will have lungs just as healthy as the average person’s.” 

This hypothesis is obviously untrue, as studies have shown again and again that cigarettes negatively affect lung health. You must be careful that your hypotheses do not reflect your own personal opinion more than they do scientifically-supported findings. This plausibility points to the necessity of research before the hypothesis is written to make sure that your hypothesis has not already been disproven.

#2: Defined Concepts

The more advanced you are in your studies, the more likely that the terms you’re using in your hypothesis are specific to a limited set of knowledge. One of the hypothesis testing examples might include the readability of printed text in newspapers, where you might use words like “kerning” and “x-height.” Unless your readers have a background in graphic design, it’s likely that they won’t know what you mean by these terms. Thus, it’s important to either write what they mean in the hypothesis itself or in the report before the hypothesis.

Here’s what we mean. Which of the following sentences makes more sense to the common person?

If the kerning is greater than average, more words will be read per minute.

If the space between letters is greater than average, more words will be read per minute.

For people reading your report that are not experts in typography, simply adding a few more words will be helpful in clarifying exactly what the experiment is all about. It’s always a good idea to make your research and findings as accessible as possible. 

Good hypotheses ensure that you can observe the results. 

#3: Observability

In order to measure the truth or falsity of your hypothesis, you must be able to see your variables and the way they interact. For instance, if your hypothesis is that the flight patterns of satellites affect the strength of certain television signals, yet you don’t have a telescope to view the satellites or a television to monitor the signal strength, you cannot properly observe your hypothesis and thus cannot continue your study.

Some variables may seem easy to observe, but if you do not have a system of measurement in place, you cannot observe your hypothesis properly. Here’s an example: if you’re experimenting on the effect of healthy food on overall happiness, but you don’t have a way to monitor and measure what “overall happiness” means, your results will not reflect the truth. Monitoring how often someone smiles for a whole day is not reasonably observable, but having the participants state how happy they feel on a scale of one to ten is more observable. 

In writing your hypothesis, always keep in mind how you'll execute the experiment.

#4: Generalizability 

Perhaps you’d like to study what color your best friend wears the most often by observing and documenting the colors she wears each day of the week. This might be fun information for her and you to know, but beyond you two, there aren’t many people who could benefit from this experiment. When you start an experiment, you should note how generalizable your findings may be if they are confirmed. Generalizability is basically how common a particular phenomenon is to other people’s everyday life.

Let’s say you’re asking a question about the health benefits of eating an apple for one day only, you need to realize that the experiment may be too specific to be helpful. It does not help to explain a phenomenon that many people experience. If you find yourself with too specific of a hypothesis, go back to asking the big question: what is it that you want to know, and what do you think will happen between your two variables?

Hypothesis Testing Examples

We know it can be hard to write a good hypothesis unless you’ve seen some good hypothesis examples. We’ve included four hypothesis examples based on some made-up experiments. Use these as templates or launch pads for coming up with your own hypotheses.

Experiment #1: Students Studying Outside (Writing a Hypothesis)

You are a student at PrepScholar University. When you walk around campus, you notice that, when the temperature is above 60 degrees, more students study in the quad. You want to know when your fellow students are more likely to study outside. With this information, how do you make the best hypothesis possible?

You must remember to make additional observations and do secondary research before writing your hypothesis. In doing so, you notice that no one studies outside when it’s 75 degrees and raining, so this should be included in your experiment. Also, studies done on the topic beforehand suggested that students are more likely to study in temperatures less than 85 degrees. With this in mind, you feel confident that you can identify your variables and write your hypotheses:

If-then: “If the temperature in Fahrenheit is less than 60 degrees, significantly fewer students will study outside.”

Null: “If the temperature in Fahrenheit is less than 60 degrees, the same number of students will study outside as when it is more than 60 degrees.”

These hypotheses are plausible, as the temperatures are reasonably within the bounds of what is possible. The number of people in the quad is also easily observable. It is also not a phenomenon specific to only one person or at one time, but instead can explain a phenomenon for a broader group of people.

To complete this experiment, you pick the month of October to observe the quad. Every day (except on the days where it’s raining)from 3 to 4 PM, when most classes have released for the day, you observe how many people are on the quad. You measure how many people come  and how many leave. You also write down the temperature on the hour. 

After writing down all of your observations and putting them on a graph, you find that the most students study on the quad when it is 70 degrees outside, and that the number of students drops a lot once the temperature reaches 60 degrees or below. In this case, your research report would state that you accept or “failed to reject” your first hypothesis with your findings.

Experiment #2: The Cupcake Store (Forming a Simple Experiment)

Let’s say that you work at a bakery. You specialize in cupcakes, and you make only two colors of frosting: yellow and purple. You want to know what kind of customers are more likely to buy what kind of cupcake, so you set up an experiment. Your independent variable is the customer’s gender, and the dependent variable is the color of the frosting. What is an example of a hypothesis that might answer the question of this study?

Here’s what your hypotheses might look like: 

If-then: “If customers’ gender is female, then they will buy more yellow cupcakes than purple cupcakes.”

Null: “If customers’ gender is female, then they will be just as likely to buy purple cupcakes as yellow cupcakes.”

This is a pretty simple experiment! It passes the test of plausibility (there could easily be a difference), defined concepts (there’s nothing complicated about cupcakes!), observability (both color and gender can be easily observed), and general explanation ( this would potentially help you make better business decisions ).

Experiment #3: Backyard Bird Feeders (Integrating Multiple Variables and Rejecting the If-Then Hypothesis)

While watching your backyard bird feeder, you realized that different birds come on the days when you change the types of seeds. You decide that you want to see more cardinals in your backyard, so you decide to see what type of food they like the best and set up an experiment. 

However, one morning, you notice that, while some cardinals are present, blue jays are eating out of your backyard feeder filled with millet. You decide that, of all of the other birds, you would like to see the blue jays the least. This means you'll have more than one variable in your hypothesis. Your new hypotheses might look like this: 

If-then: “If sunflower seeds are placed in the bird feeders, then more cardinals will come than blue jays. If millet is placed in the bird feeders, then more blue jays will come than cardinals.”

Null: “If either sunflower seeds or millet are placed in the bird, equal numbers of cardinals and blue jays will come.”

Through simple observation, you actually find that cardinals come as often as blue jays when sunflower seeds or millet is in the bird feeder. In this case, you would reject your “if-then” hypothesis and “fail to reject” your null hypothesis . You cannot accept your first hypothesis, because it’s clearly not true. Instead you found that there was actually no relation between your different variables. Consequently, you would need to run more experiments with different variables to see if the new variables impact the results.

Experiment #4: In-Class Survey (Including an Alternative Hypothesis)

You’re about to give a speech in one of your classes about the importance of paying attention. You want to take this opportunity to test a hypothesis you’ve had for a while: 

If-then: If students sit in the first two rows of the classroom, then they will listen better than students who do not.

Null: If students sit in the first two rows of the classroom, then they will not listen better or worse than students who do not.

You give your speech and then ask your teacher if you can hand out a short survey to the class. On the survey, you’ve included questions about some of the topics you talked about. When you get back the results, you’re surprised to see that not only do the students in the first two rows not pay better attention, but they also scored worse than students in other parts of the classroom! Here, both your if-then and your null hypotheses are not representative of your findings. What do you do?

This is when you reject both your if-then and null hypotheses and instead create an alternative hypothesis . This type of hypothesis is used in the rare circumstance that neither of your hypotheses is able to capture your findings . Now you can use what you’ve learned to draft new hypotheses and test again! 

Key Takeaways: Hypothesis Writing

The more comfortable you become with writing hypotheses, the better they will become. The structure of hypotheses is flexible and may need to be changed depending on what topic you are studying. The most important thing to remember is the purpose of your hypothesis and the difference between the if-then and the null . From there, in forming your hypothesis, you should constantly be asking questions, making observations, doing secondary research, and considering your variables. After you have written your hypothesis, be sure to edit it so that it is plausible, clearly defined, observable, and helpful in explaining a general phenomenon.

Writing a hypothesis is something that everyone, from elementary school children competing in a science fair to professional scientists in a lab, needs to know how to do. Hypotheses are vital in experiments and in properly executing the scientific method . When done correctly, hypotheses will set up your studies for success and help you to understand the world a little better, one experiment at a time.

What’s Next?

If you’re studying for the science portion of the ACT, there’s definitely a lot you need to know. We’ve got the tools to help, though! Start by checking out our ultimate study guide for the ACT Science subject test. Once you read through that, be sure to download our recommended ACT Science practice tests , since they’re one of the most foolproof ways to improve your score. (And don’t forget to check out our expert guide book , too.)

If you love science and want to major in a scientific field, you should start preparing in high school . Here are the science classes you should take to set yourself up for success.

If you’re trying to think of science experiments you can do for class (or for a science fair!), here’s a list of 37 awesome science experiments you can do at home

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Ashley Sufflé Robinson has a Ph.D. in 19th Century English Literature. As a content writer for PrepScholar, Ashley is passionate about giving college-bound students the in-depth information they need to get into the school of their dreams.

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Moon Formation

How did the moon form.

Earth’s Moon was born out of destruction.

Several theories about our Moon’s formation vie for dominance, but almost all share that point in common: near the time of the solar system’s formation, about 4.5 billion years ago, something ― perhaps a single object the size of Mars, perhaps a series of objects ― crashed into the young Earth and flung enough molten and vaporized debris into space to create the Moon.

The early solar system would have been a chaotic, terrifying place. Debris left over from the formation of the Sun coalesced into a disk around the star, creating clumps that ranged in size from dust flecks to minor planets. Gravity drew these objects together, causing them to crash into each other ― violent smashups that could end in obliteration or new, larger objects. Those mashed-together objects make up the planets, moons, asteroids and other solar system objects we know today.

Written in Stone

Visiting the Moon with the Apollo missions in the late 1960s and early 1970s revolutionized our understanding of the Moon’s origins. Previous concepts ― that the Moon was an object captured by Earth’s gravity as it sailed by, or that the Moon formed alongside Earth from the same debris ― fell out of favor after the Apollo missions brought back data and 842 pounds (382 kilograms) of lunar samples to Earth in the late 1960s and early 1970s. The Apollo evidence all pointed to the Moon forming from a large impact. The age of the rock samples indicated that the Moon formed around 60 million years after the solar system began to form. The type and composition of the samples showed that the Moon had been molten during its formation and was covered with a deep ocean of magma for tens of millions to hundreds of millions of years ― an environment that would occur in the aftermath of an intensely energetic impact. Lunar rocks were found to contain only small amounts of elements that vaporize when heated, further indicating the Moon could have formed in a high-energy impact that let those elements escape.

Five Things We Learned from Apollo Moon Rocks

• The chemical composition of Moon and Earth rocks are very similar.
• The Moon was once covered in an ocean of magma.
• Meteorites have shattered and melted rocks on the Moon’s surface through impacts.
• Lava flowed up through cracks in the Moon’s crust and filled its impact basins.
• Lunar “soil” is made of pulverized rock created by meteorite impacts.

Perhaps most importantly, the rock samples indicated that the Moon was once a part of Earth. Basaltic rocks from the Moon’s mantle have striking similarities to basaltic rocks from Earth’s mantle. The oxygen  isotopes  and other elements sealed into the specimens matched those of Earth rocks too precisely for the similarities to be a coincidence.

Meteorites make up another body of evidence. Samples collected by Apollo astronauts come from just a few sites on the Moon, but lunar meteorites ― rocks sent into space by impacts on the Moon that eventually find their way to Earth ― provide samples from all over the Moon that tell a similar tale of the Moon’s history. Meteorites originating from asteroids have also been used to help confirm the timeline of the Moon’s formation. Some show signs of having been  bombarded by debris  from the giant, Moon-forming impact.

Finally, more recent studies add the evidence for a high-energy impact that resulted in the creation of a molten Moon. Analysis of light reflecting off the Moon gives details of the mineral makeup of the Moon’s surface, and it shows the widespread presence of anorthosite, an igneous rock that crystallizes out of and floats to the top of magma. The presence of anorthosite across the Moon’s surface reinforces that the Moon must once have been covered by a widespread magma ocean that was quite deep, from hundreds to thousands of kilometers.

Lunar “Archaeology”

Though Earth and Moon both came from that ancient collision ― and Earth is certainly within easier reach ― studying the Moon gives us our best chance of understanding what happened all those billions of years ago. Earth’s active geological processes, from plate tectonics to erosion, erase the evidence of formation. Aside from events like impacts, much of the Moon’s surface changes on a vastly slower timescale. Like detectives at a crime scene, scientists use clues preserved on the lunar surface to piece together the Moon’s history. Any improvements to the giant impact theory or a new theory would need to explain what we observe of the Moon today.

One of the oddities is the Moon’s low iron content as compared with Earth’s. Earth’s iron-rich core accounts for around 30 percent of its mass, but the core of the Moon is only about 1.6-1.8 percent of its total mass. One possible explanation is that the energy of the impact with Earth that formed the Moon vaporized lighter materials, casting them into space, and left behind heavier elements ― such as iron, which vaporizes only at extremely high temperatures ― to sink into Earth’s core.

Any viable theory of lunar formation also has to explain where the Moon is now in relation to Earth and the speed and inclination of its orbit. Surface reflectors placed on the Moon during Apollo show that the Moon moves away from Earth at the rate of about an inch and a half per year. This indicates that the Moon initially formed much closer to our planet, and, therefore, that the early Earth’s spin rate was much higher than it is today. Computer models created by scientists to test and analyze Moon formation theories must show how a massive collision can produce the existing orbits and rotation of Moon and Earth over billions of years when paired with the typical gravitational interactions between the two bodies. (Even today, the distance between the Earth and Moon, and the length of a day on Earth, continues to grow due to the effects of Earth’s tides .)

Finally, strange discrepancies exist between the Moon’s near and far sides. Differences include: the thickness of the crust ― 43 miles (70 kilometers) on the Moon's near-side versus 93 miles (150 kilometers) on the far side; the contrasting geological makeup, including a concentration of radioactive elements on the near side; and the rich history of volcanism on the near side compared with a relative lack of volcanic activity on the far side. How closely these differences are related to the Moon’s formation ― how it cooled, how its volcanic activity took place, and the manner in which it has been bombarded by objects from space ― is a question scientists continue to wrestle with today.

Model Behavior

With humanity’s return to the Moon through the Artemis program, scientists expect a flood of new information that will help us hone in on a single formation scenario. In the meantime, scientists continue to study existing samples and other information they have now ― such as information from lunar orbiters and the growing body of knowledge on planetary formation ― to construct computer models that help us understand how the collision might have happened, and how it could have resulted in the Moon and Earth as we see them today. The models account for factors like the strength of the colliding objects, the friction between the components, the density of the components, and how materials behave under different temperatures and pressures. Today’s advanced computer models can provide a number of very specific outcomes based on variables like these.

For instance, when scientists want to figure out why the Moon is low in certain elements that vaporize easily, they use models to see how the Moon’s composition would look if the elements were lost, or depleted, during different periods of the Moon’s formation. Perhaps the environment in which the Moon formed or early eruptions on the Moon’s surface created a temporary atmosphere that led to the elimination of some of those elements, or they may have been released through interactions with the heat of the Sun or a bright and still-molten Earth.

Even these complex models can’t simulate every atom in a massive collision between giant objects that kicks debris into space. But astronomers can represent larger groups of debris by using particles whose properties depend on where they are located during the collision, like hot material situated near the proto-Moon’s core. Astronomers are able to alter the properties in their models to produce different results, showing how even small changes can produce different scenarios. As evidence continues to come in, the eventual goal is a comprehensive model that accounts for everything we know about the Moon.

Searching for the Past in the Future

The final Apollo Moon mission was in 1972. Scientists have had decades to investigate lunar samples and data from the Apollo missions, combine it with information returned by subsequent lunar missions, come to conclusions, and form new questions. They know what to target during the upcoming Artemis missions to help solve some of the outstanding mysteries.

All of the Apollo missions landed near the Moon’s equator, and the samples brought back are mostly from volcanic regions. Lunar scientists are hoping to obtain new samples from different locations, like the far side of the Moon and areas closer to the poles, so they can examine the Moon’s composition in regions that would have evolved in different ways and uncover more evidence of how the Moon formed. They’re hoping to drill down into the lunar surface and acquire core samples that expose additional layers of the Moon’s geologic history, a record written in rock and mostly hidden from us for now.

These new discoveries will help narrow down the many unknown factors in the Moon formation models. If the new evidence shows ― to choose just one example ― that a vast quantity of sulfur was lost during a period of volcanic activity, then that sulfur loss doesn’t need to be accounted for during early stages of Moon formation. Like a game of Clue, deciphering the mysteries of the Moon’s formation will be a process of elimination, ruling out particular events happening during certain time periods and narrowing down the possibilities until few remain.

But scientists are also alert to the possibility of new discoveries, findings that paint a different picture. The greatest clues to the Moon’s past may still be scattered around and beneath the lunar surface, waiting to be unearthed.

Writer: Tracy Vogel Science Advisors: Prabal Saxena (NASA's Goddard Space Flight Center), Sarah Valencia (NASA's Goddard Space Flight Center) and Bill Bottke (Southwest Research Institute Boulder)

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How did the Moon form?

Museum planetary science researcher Prof Sara Russell explains the origins of Earth's closest companion.

Analysis of samples brought back from the NASA Apollo missions suggest that the Earth and Moon are a result of a giant impact between an early proto-planet and an astronomical body called Theia.

Moon origin theories

'There used to be a number of theories about how the Moon was made and it was one of the aims of the Apollo program to figure out how we got to have our Moon,' says Sara.

Prior to the Apollo mission research there were three theories about how the Moon formed. The evidence returned from these missions gave us today's most widely accepted theory. 

• Capture theory suggests that the Moon was a wandering body (like an asteroid ) that formed elsewhere in the solar system and was captured by Earth's gravity as it passed nearby.
• The accretion hypothesis proposes that the Moon was created along with Earth at its formation.
• The fission theory  suggests Earth had been spinning so fast that some material broke away and began to orbit the planet.
• The giant-impact theory is most widely accepted today. This proposes that the Moon formed during a collision between the Earth and another small planet, about the size of the planet Mars . The debris from this impact collected in an orbit around Earth to form the Moon.

Lunar meteorite Dar al Gani 400. In 1998, this specimen was found in the Sahara Desert, in Libya. 

Moon rocks from the Apollo missions

The Apollo missions brought back over a third of a tonne of rock and soil from the Moon. This provided some clues on how the Moon may have formed.

'When the Apollo rocks came back, they showed that the Earth and the Moon have some remarkable chemical and isotopic similarities, suggesting that they have a linked history,' says Sara.

'If the Moon had been created elsewhere and was captured by the Earth's gravity we would expect its composition to be very different from the Earth's.

'If the Moon was created at the same time, or broke off the Earth, then we would expect the type and proportion of minerals on the Moon to be the same as on Earth. But they are slightly different.'

This thumbnail-sized piece of Moon rock was gifted to the Museum by President Nixon in 1973. It was collected during the last Apollo space mission. Find out more about our links to the Apollo missions . 

The minerals on the Moon contain less water than similar terrestrial rocks. The Moon is rich in material that forms quickly at a high temperature. 

'In the seventies and eighties there was a lot of debate which led to an almost universal acceptance of the giant impact model.'

Lunar meteorites are also an important source of data for studying the origins of the Moon.

'In some ways meteorites can tell us more about the Moon than Apollo samples because meteorites come from all over the surface of the Moon,' adds Sara, 'while Apollo samples come from just one place near the equator on the near side of the Moon.'

Proto-Earth and Theia

Before Earth and the Moon, there were proto-Earth and Theia (a roughly Mars-sized planet).

The giant-impact model suggests that at some point in Earth's very early history, these two bodies collided.

The Moon may have formed in the wake of a collision between an early proto-planet and an astronomical body called Theia. © Fernando Astasio Avila/ Shutterstock

During this massive collision, nearly all of Earth and Theia melted and reformed as one body, with a small part of the new mass spinning off to become the Moon as we know it.

Scientists have experimented with modelling the impact, changing the size of Theia to test what happens at different sizes and impact angles, trying to get the nearest possible match.

'People are now tending to gravitate towards the idea that early Earth and Theia were made of almost exactly the same materials to begin with, as they were within the same neighbourhood as the solar system was forming,' explains Sara.

'If the two bodies had come from the same place and were made of similar stuff to begin with, this would also explain how similar their composition is.'

The surface of the Moon

The mineralogy of Earth and the Moon are so close that it's possible to observe Moon-like landscapes without jetting off into space.

'If you look at the lunar surface, it looks pale grey with dark splodges,' Sara says. 'The pale grey is a rock called anorthosite. It forms as molten rock cools down and lighter materials float to the top, and the dark areas are another rock type called basalt.'

What are the dark spots on the Moon?

Similar anorthosite can be seen on the Isle of Rum in Scotland. What's more, most of the ocean floor is basalt - it's the most common surface on all the inner planets in our solar system.

'However, what is really special on the Moon, that we can't ever replicate on Earth, is that the Moon is geologically rather dead,' Sara says.

The Moon hasn't had volcanoes for billions of years, so its surface is remarkably unchanged. This is also why impact craters are so clear.

By looking at the Moon we can tell a lot about what the Earth was like four billion years ago.

Prof Sara Russell explains more about the Moon's formation:

A balancing influence.

Having a moon as large as ours is something that's unique in our solar system.

'While other planets have tiny moons, the Earth's Moon is almost the size of Mars,' Sara says.

'If you look at other similar planets to ours, they wobble quite a lot in their orbit (the North Pole moves) and as a result the climate is much more unpredictable.'

A piece of Anorthosite breccia moon rock displayed in a glass prism

The Moon has helped stabilise Earth's orbit and reduced polar motion. This has aided in producing our planet's relatively stable climate.

'It's a subject of quite a lot of scientific debate as to how important the Moon has been in making it possible for life to exist on Earth.'

Find out how the Moon affects life on Earth .

Does Earth have more than one moon?

There may indeed be several objects in orbit around Earth. But to the best of our knowledge they are objects that the planet has drawn into its orbit - most likely captured asteroids. These natural satellites don't share the same important history as the Moon and they likely exist only temporarily in Earth's orbit.

See a piece of the Moon at the Museum

Explore gems and minerals, including a piece of Apollo Moon rock, in the Museum's Earth galleries .

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Formation of The Moon

The Moon, Earth’s only natural satellite, has captivated human fascination for centuries and plays a crucial role in shaping our planet’s dynamics.

Characteristics of the Moon:

• Size and Distance: The Moon is about 1/6th the size of Earth, with a diameter of approximately 3,474 kilometers. It orbits Earth at an average distance of about 384,400 kilometers.
• Gravity: Lunar gravity is much weaker than Earth’s, about 1/6th of our planet’s gravity. This property has interesting implications for human exploration and potential future lunar colonies.
• Surface Features: The Moon’s surface is marked by various features, including impact craters, mountains, valleys, and lunar maria (large, dark plains formed by ancient volcanic activity).
• Rotation and Orbit: The Moon is tidally locked to Earth, meaning it always shows the same face to our planet. Its orbit and rotation period around Earth are approximately 27.3 days, matching its rotation period.

Importance of the Moon:

• Tides: The Moon’s gravitational pull influences Earth’s tides. The gravitational interaction between Earth and the Moon creates tides, which play a crucial role in oceanic and coastal dynamics.
• Scientific Research: Studying the Moon provides insights into the early solar system and the processes that shaped terrestrial planets. The lunar surface also serves as a record of cosmic impacts over time.
• Space Exploration Platform: The Moon has been a significant target for space exploration missions. Its proximity makes it an ideal location for testing new technologies and conducting scientific experiments, serving as a stepping stone for future deep-space exploration.
• Astronomical Observations: The Moon’s absence of atmosphere makes it an excellent platform for astronomical observations. Telescopes on the Moon could observe the universe without the distortion caused by Earth’s atmosphere.

Significance of Studying the Moon’s Formation:

• Planetary Evolution: Understanding how the Moon formed provides essential clues about the early history and evolution of the entire solar system. The Moon’s composition and structure are key pieces of the puzzle in reconstructing the processes that led to the formation of planets.
• Earth-Moon Relationship: The study of the Moon’s formation helps us understand the relationship between Earth and its satellite. It is widely believed that a giant impact between Earth and a Mars-sized body led to the formation of the Moon, and exploring this event sheds light on Earth’s early history.
• Cosmic Impact History: The Moon’s surface, marked by countless impact craters, preserves a record of the solar system’s early bombardment history. Analyzing lunar impact data contributes to our understanding of the broader impact history in the inner solar system.

In summary, the Moon is not only a celestial companion that influences Earth’s tides but also a valuable object of scientific inquiry, space exploration, and a witness to the early history of our solar system. Studying its formation enhances our understanding of planetary evolution and the dynamic processes that shaped the worlds within our cosmic neighborhood.

Giant Impact Hypothesis

Pre-collision earth: earth’s early conditions and composition, the impact event: collision between earth and the impactor, formation of a proto-lunar disk, accretion of the moon, composition of the moon, evidence supporting the giant impact hypothesis, alternative theories, post-formation evolution, conclusion: recap of key points in the moon’s formation.

The Giant Impact Hypothesis, also known as the Theia Impact or the Big Whack, is a widely accepted scientific explanation for the formation of the Moon. It proposes that the Moon was created as a result of a massive collision between Earth and a Mars-sized protoplanet called Theia, early in the history of the solar system.

Conditions Leading to the Proposed Collision:

The scenario leading to the giant impact is thought to have occurred around 4.5 billion years ago, during a period known as the Late Heavy Bombardment. The key conditions leading to this proposed collision include:

• Early Solar System Dynamics: In the early stages of the solar system, numerous protoplanets and planetesimals orbited the Sun. The gravitational interactions and migrations of these bodies set the stage for potential collisions.
• Formation of Theia: Theia, the hypothetical protoplanet involved in the collision, is believed to have formed in a similar region of the solar system as Earth. Its name is derived from Greek mythology, where Theia was a Titan and the mother of the Moon goddess Selene.
• Orbital Dynamics: Theia’s orbit is thought to have eventually become destabilized, leading it on a collision course with Earth. The specifics of this orbital instability are complex and involve gravitational interactions with other bodies in the early solar system.
• Collision: The collision itself was an incredibly energetic event. Theia collided with the young Earth at a high velocity, releasing an immense amount of energy. The impact led to the ejection of debris, which eventually coalesced to form the Moon.

Simulation Models Supporting the Hypothesis:

Numerical simulations and modeling have played a crucial role in supporting the Giant Impact Hypothesis. These simulations take into account the laws of physics, including gravitational interactions, material properties, and the dynamics of celestial bodies. Here are some key points supported by simulation models:

• Debris Formation: Simulations show that the collision between Earth and Theia would have generated a significant amount of debris. This debris was then expected to form a disk of molten material around Earth.
• Moon Formation: The debris in the accretion disk gradually came together to form the Moon. This process, called accretion, involved the gravitational attraction and merging of countless small particles into larger bodies.
• Angular Momentum Conservation: The simulations explain how angular momentum is conserved in the system. The rotation of the Earth-Moon system is a key outcome of the collision, and the models show how the final configuration of the Earth-Moon system reflects the conservation of angular momentum.
• Isotope Ratios: The chemical composition of the Moon is found to be similar to Earth’s mantle, supporting the idea that the Moon originated from Earth. However, the Moon has a lower iron content, consistent with the expectation that the impacting body (Theia) contributed to the Moon’s formation.

In summary, the Giant Impact Hypothesis provides a compelling explanation for the origin of the Moon, and numerical simulations offer support by demonstrating how the collision between Earth and Theia could have led to the formation of our planet’s natural satellite. These simulations help scientists understand the dynamics of early solar system events and the processes that shaped the terrestrial planets.

Understanding the conditions of pre-collision Earth is crucial for comprehending the dynamics that led to the formation of the Moon. Around 4.5 billion years ago, during the early stages of the solar system, Earth was undergoing a series of transformative processes. Here are key aspects of Earth’s early conditions and composition:

• Formation: Earth formed through accretion, a process in which smaller planetesimals and protoplanets collided and merged to create a larger body. This process led to the differentiation of Earth’s interior into distinct layers, with heavy metals like iron and nickel sinking to the core, and lighter materials forming the mantle and crust.
• Molten State: In its early stages, Earth was predominantly molten due to the heat generated during the accretion process and the energy released by the decay of radioactive isotopes. This molten state allowed for the segregation of materials based on density.
• Atmosphere and Hydrosphere: Earth’s early atmosphere was likely composed of volatile compounds like water vapor, carbon dioxide, methane, and ammonia. The presence of water vapor eventually condensed, leading to the formation of Earth’s primitive oceans and the beginning of the hydrosphere.
• Heavy Bombardment: During the Late Heavy Bombardment period, which occurred roughly 4.1 to 3.8 billion years ago, Earth experienced intense impacts from leftover planetesimals and protoplanets. These impacts played a significant role in shaping the early Earth and may have contributed to the eventual formation of the Moon.

Proto-Moon or Pre-existing Celestial Bodies:

The question of whether Earth had a proto-Moon or pre-existing celestial bodies before the giant impact is a topic of scientific investigation. Some models propose the existence of a small moon or moonlets in orbit around Earth prior to the giant impact. Here are a few considerations:

• Co-formation Hypothesis: Some models suggest that the Moon formed alongside Earth during the accretion process. According to this co-formation hypothesis, a series of smaller moonlets or proto-Moons may have coalesced to form a larger Moon. These moonlets could have been remnants of the material from which Earth itself was forming.
• Capture Hypothesis: Another hypothesis proposes that the Moon was captured by Earth’s gravity from its original orbit around the Sun. However, the likelihood of such a capture is considered to be low, as it would require specific conditions that are not commonly found in the solar system.
• Collision and Debris: The prevailing Giant Impact Hypothesis suggests that the Moon formed from the debris ejected during a collision between Earth and a Mars-sized protoplanet (Theia). In this scenario, there was no pre-existing Moon, and the collision itself led to the creation of the Moon from the resulting debris disk.

While the precise details of Earth’s early conditions and the presence of a proto-Moon or pre-existing celestial bodies are still areas of active research, the Giant Impact Hypothesis remains the most widely accepted explanation for the Moon’s formation. This hypothesis provides a coherent and well-supported narrative for the events that led to the creation of Earth’s natural satellite.

The impact event that led to the formation of the Moon was an incredibly violent and energetic collision between Earth and a Mars-sized protoplanet called Theia. Here’s a description of the key stages of the impact:

• Approach and Orbital Dynamics: Theia, on a collision course with Earth, approached our planet at a high velocity. The specifics of the collision were influenced by the orbital dynamics of both bodies, with gravitational forces playing a significant role in determining the trajectory and energy of the impact.
• Contact: As Theia collided with Earth, an immense amount of energy was released. The impact would have been so powerful that it led to the deformation and disruption of both the impacting body and Earth’s surface.
• Ejection of Debris: The impact resulted in the ejection of a large amount of debris from both Earth and Theia. This debris was propelled into space, forming an accretion disk around Earth.
• Accretion Disk Formation: The debris, consisting of molten and vaporized rock, formed a swirling disk of material around Earth. This disk extended into space and gradually coalesced due to gravitational interactions.

Energy Release, Heat, and Formation of a Molten Mass:

The collision between Earth and Theia released an extraordinary amount of energy, transforming a significant portion of the impacted region into a molten mass. Here are key aspects of this process:

• Energy Release: The energy released during the impact was immense, equivalent to a staggering amount of kinetic and gravitational potential energy being converted into heat. This energy release contributed to the extreme temperatures generated during the collision.
• Heat Generation: The impact generated intense heat due to the conversion of kinetic energy into thermal energy upon collision. The temperatures reached were high enough to melt a substantial portion of Earth’s surface and the impacting body, creating a molten, partially vaporized mass.
• Molten Mass Formation: The heat generated by the impact caused the impacted region to melt and form a molten mass. This molten material, consisting of rock and metal from both Earth and Theia, contributed to the creation of the accretion disk around Earth.
• Accretion of the Moon: Over time, the molten material in the accretion disk began to cool and solidify. Through the process of accretion, small particles within the disk began to clump together, forming larger and larger bodies. Ultimately, these processes led to the coalescence of material into the Moon.

The aftermath of the impact event resulted in the formation of the Moon and marked a critical phase in the early history of both Earth and the Moon. The debris ejected into space eventually came together to create the Moon, and the energy released during the collision played a fundamental role in shaping the characteristics of Earth’s natural satellite.

The formation of a proto-lunar disk was a crucial step in the process that eventually led to the creation of the Moon. This disk formed as a result of the immense energy released during the collision between Earth and the impactor, Theia. Here’s a detailed explanation of how the debris and materials ejected into space contributed to the formation of a disk around Earth:

• The high-velocity impact between Earth and Theia resulted in the violent ejection of a significant amount of material from both bodies.
• This ejected material consisted of molten rock, vaporized substances, and fragments from the impacting bodies. The composition included elements from Earth’s mantle, crust, and Theia.
• The ejected material did not escape Earth’s gravitational influence completely. Instead, it formed a swirling disk of debris in orbit around Earth.
• The gravitational forces acting on the debris caused it to spread out and take the form of a disk-shaped structure encircling Earth.
• The proto-lunar disk was composed of molten and vaporized rock, as well as other materials that were present in the colliding bodies.
• The intense heat generated by the impact kept the material in the disk in a molten or partially vaporized state.
• The conservation of angular momentum played a crucial role in the formation of the proto-lunar disk. As the impacting body and Earth collided, their combined angular momentum influenced the motion of the debris.
• This conservation principle led to the rotation of the proto-lunar disk in the same direction as Earth’s rotation.
• Within the proto-lunar disk, small particles began to accrete and collide due to gravitational attraction. This process led to the formation of larger and larger bodies within the disk.
• Over time, these accreted bodies merged to form protomoonlets and, eventually, the Moon itself. The gradual coalescence of material within the disk resulted in the solidification of the Moon as it grew in size.
• The proto-lunar disk influenced the orbital dynamics of the system. As the Moon formed within the disk, it interacted with the surrounding material and adjusted its orbit over time.

The formation of the proto-lunar disk represents a critical phase in the Giant Impact Hypothesis, providing a mechanism for the creation of the Moon from the debris ejected during the collision. This swirling disk of molten material, shaped by gravitational forces and angular momentum conservation, laid the foundation for the subsequent accretion and consolidation of material into Earth’s natural satellite.

The accretion of the Moon involved the gradual coming together and merging of smaller bodies within the proto-lunar disk, driven by gravitational forces. As these bodies accreted, they formed larger and larger structures until the Moon took shape. Here’s a detailed explanation of the accretion process and the subsequent cooling and solidification of the Moon:

1. Gravitational Forces and Accretion:

• Within the proto-lunar disk, individual particles, protomoonlets, and smaller bodies experienced gravitational attraction toward one another.
• Gravitational forces caused these particles to come together, forming larger aggregates. As these aggregates grew, their gravitational pull increased, facilitating the accretion of more material.

2. Formation of Protomoonlets:

• Initially, small protomoonlets formed as a result of the accretion process. These were intermediate-sized bodies that continued to grow by attracting additional material within the disk.

3. Collisions and Growth:

• Larger bodies within the proto-lunar disk collided with one another, leading to the formation of even larger structures.
• Over time, the process of collisions and accretion resulted in the development of protomoonlets of substantial size.

4. Continued Accretion:

• Gravitational interactions persisted, causing protomoonlets to attract more material and merge with neighboring bodies.
• The largest of these protomoonlets exerted stronger gravitational influence, leading to their dominance in the ongoing accretion process.

5. Moon Formation:

• As the accretion continued, one dominant body emerged, gradually accumulating most of the material within the proto-lunar disk.
• This dominant body evolved into the Moon, representing the culmination of the accretion process.

6. Cooling and Solidification:

• As the Moon formed and grew in size, the heat generated during the accretion process began to dissipate.
• The cooling of the Moon occurred as the heat was radiated away into space. This cooling process led to the solidification of the Moon’s surface and interior.

7. Differentiation:

• The cooling and solidification of the Moon allowed for the differentiation of its interior. Heavier materials sank toward the Moon’s core, while lighter materials rose to the surface, a process similar to the early differentiation of Earth.

8. Final Configuration:

• Over a considerable period, the Moon reached its final configuration as a solid, differentiated body with a surface composed of solidified rock.
• The Moon’s rotation became tidally locked with Earth, meaning it always shows the same face to our planet.

The accretion of the Moon was a dynamic process influenced by gravitational interactions, angular momentum conservation, and the orbital dynamics within the proto-lunar disk. The subsequent cooling and solidification of the Moon resulted in the formation of the lunar surface and the establishment of the Moon as Earth’s natural satellite.

The Moon is composed of various materials that provide insights into its formation and evolution. The primary components of the Moon’s composition include:

• The lunar crust is predominantly composed of rocks rich in aluminum and silica, known as anorthosite . Anorthosite is formed from the solidification of molten material during the Moon’s early history.
• Beneath the crust lies the lunar mantle, which is composed of denser rock materials such as pyroxene and olivine . These materials are remnants from the Moon’s early molten state.
• Unlike Earth, the Moon does not have a large, liquid outer core. Instead, any metallic core is thought to be small and partially solidified, primarily composed of iron and nickel.
• The Moon’s surface is marked by various features, including impact craters, lunar maria (large, dark plains formed by ancient volcanic activity), mountains, and valleys. These features result from a combination of volcanic activity, impact events, and the Moon’s geological history.
• The lunar regolith is a layer of loose, fragmented material that covers the Moon’s surface. It consists of fine-grained particles produced by the continual bombardment of the Moon by micrometeoroids and larger impactors.
• Recent discoveries suggest the presence of water ice in permanently shadowed regions near the lunar poles. This finding has implications for future lunar exploration and potential resource utilization.

Differentiation of Materials within the Moon:

The Moon’s composition and structure exhibit signs of differentiation, a process that involves the separation and sinking of denser materials toward the center, while lighter materials rise to the surface. Here’s an overview of the differentiation of materials within the Moon:

• During the Moon’s early history, when it was in a molten or partially molten state, differentiation began. Heavier materials, such as iron and nickel, sank toward the lunar core, while lighter materials, like aluminum and silica, rose to form the crust.
• The solidification of the lunar magma ocean led to the formation of the anorthositic crust. Anorthosite rocks, rich in aluminum and silica, represent the primary components of the lunar crust.
• The lunar mantle, lying beneath the crust, is composed of denser rocks like pyroxene and olivine. These materials are remnants from the early differentiation process and provide insight into the Moon’s internal structure.
• While the Moon is thought to have a small metallic core, it is not as extensively differentiated as Earth’s core. The Moon’s core likely contains a mixture of iron and nickel, and it may be partially solidified.
• The Moon’s surface features, including impact craters and lunar maria, are the result of subsequent geological processes that have shaped the lunar landscape. Impact events have played a significant role in modifying the Moon’s surface over time.

Understanding the composition and differentiation of the Moon’s materials provides valuable information about the early solar system, the Moon’s formation, and the processes that shaped terrestrial bodies in our cosmic neighborhood. Ongoing scientific exploration and study of lunar samples contribute to refining our understanding of the Moon’s complex history.

The Giant Impact Hypothesis, which proposes that the Moon formed as a result of a massive collision between Earth and a Mars-sized protoplanet (Theia), is supported by various lines of evidence, including Moon rock samples, isotopic ratios, and orbital characteristics. Here’s an overview of these supporting pieces of evidence:

• The analysis of lunar rock samples brought back by the Apollo missions reveals striking similarities between the composition of the Moon’s crust and Earth’s crust.
• Both the Moon’s anorthositic crust and Earth’s crust are rich in aluminum and silica, specifically in the form of anorthosite rocks. This similarity supports the idea that the Moon formed from material that originated on Earth.
• Isotopic analysis of Moon rock samples has provided crucial evidence supporting the Giant Impact Hypothesis.
• The isotopic ratios of oxygen, titanium , and other elements in lunar rocks closely match those found in Earth’s mantle, indicating a connection between the Moon and Earth’s composition.
• The similarity in isotopic ratios supports the idea that the Moon’s material originated from both Earth and the impacting body (Theia).
• The Giant Impact Hypothesis predicts certain characteristics of the Earth-Moon system that align with observations.
• The conservation of angular momentum during the impact event is reflected in the current orbital characteristics of the Moon, including its rotation period and its synchronous rotation with Earth. This alignment supports the hypothesis that the Moon formed from the debris ejected during a high-energy impact.
• Numerical simulations and modeling of the collision between Earth and Theia provide additional support for the Giant Impact Hypothesis.
• These simulations demonstrate how the impact could have led to the ejection of debris, the formation of an accretion disk, and the subsequent coalescence of material into the Moon.
• The Moon’s relatively small or non-existent iron core is consistent with the Giant Impact Hypothesis. The impacting body, Theia, may have contributed little to no iron to the forming Moon, explaining the Moon’s composition.
• The lunar maria, large plains on the Moon’s surface, are thought to have formed from volcanic activity that occurred after the giant impact.
• This volcanic activity is consistent with the presence of a molten state during the Moon’s early history, as predicted by the Giant Impact Hypothesis.

In summary, the Giant Impact Hypothesis is supported by a convergence of evidence, including the composition of Moon rock samples, isotopic ratios, orbital characteristics, and the results of numerical simulations. The consistent findings from multiple lines of inquiry strengthen the scientific consensus regarding the Moon’s formation through a colossal collision event in the early history of our solar system.

While the Giant Impact Hypothesis is widely accepted as the leading explanation for the Moon’s formation, alternative theories have been proposed. Here are a couple of alternative theories, along with a brief comparison of their strengths and weaknesses:

• The Double Planet Hypothesis suggests that the Moon formed as a result of the gravitational capture of a celestial body that was passing by Earth. This passing body would have been captured into orbit around Earth, eventually becoming the Moon.
• It doesn’t rely on a massive collision, potentially avoiding some of the challenges associated with the energy requirements of the Giant Impact Hypothesis.
• The mechanics of gravitational capture are complex, and it is challenging for a celestial body to be captured into a stable orbit around Earth without a significant energy transfer. This hypothesis faces challenges in explaining the observed isotopic similarities between the Moon and Earth.
• The Fission Hypothesis suggests that the Moon was once part of Earth and was separated from it early in the planet’s history. This separation could have been caused by the rapid rotation of a young Earth, leading to material being ejected and forming the Moon.
• It accounts for the isotopic similarities between the Moon and Earth.
• The hypothesis doesn’t require an external impacting body.
• The energy required to separate a portion of Earth and form the Moon through fission is considered to be impractical.
• It is challenging to explain the current angular momentum and orbital characteristics of the Earth-Moon system using this hypothesis.

Comparison of Strengths and Weaknesses:

• Consistent with the observed isotopic similarities between the Moon and Earth.
• Explains the angular momentum and orbital characteristics of the Earth-Moon system.
• Supported by numerical simulations.
• Challenges related to the energy requirements of the impact event.
• Doesn’t rely on a massive collision.
• Faces challenges in explaining isotopic similarities.
• Complex mechanics of gravitational capture.
• Accounts for isotopic similarities.
• Doesn’t require an external impacting body.
• Impractical energy requirements for the fission process.
• Challenges in explaining current angular momentum and orbital characteristics.

In summary, each hypothesis has its strengths and weaknesses. The Giant Impact Hypothesis remains the most widely accepted due to its ability to account for multiple lines of evidence, including isotopic similarities and orbital characteristics. However, ongoing research and advances in planetary science may lead to further refinement or new theories regarding the Moon’s formation.

The post-formation evolution of the Moon is characterized by a complex interplay of geological processes that have shaped its surface and interior. Here’s an overview of the early history of the Moon, including impact cratering, volcanic activity, and other significant geological processes:

1. Early Bombardment (4.5 to 3.8 billion years ago):

• The Moon’s early history was marked by a period of intense bombardment known as the Late Heavy Bombardment (LHB). During this time, the Moon, along with other bodies in the solar system, experienced a high frequency of impact events from leftover planetesimals and asteroids.

2. Formation of Impact Basins:

• Large impact events during the early bombardment created basins, some of which later became filled with lava, forming lunar maria. Notable impact basins include Imbrium, Serenitatis, Crisium, and others.

3. Lunar Maria Formation (3.8 to 3.2 billion years ago):

• The lunar maria are large, dark plains on the Moon’s surface. These areas were formed by volcanic activity that occurred after the early bombardment. Lava flows filled the impact basins, creating the smooth, dark regions visible on the Moon.

4. Decline in Volcanic Activity:

• The Moon’s volcanic activity declined over time, and the most recent volcanic activity is thought to have occurred around 1 billion years ago. The decline may be related to the Moon’s cooling interior and decreasing availability of molten material.

5. Regolith Formation:

• The continuous bombardment of the Moon’s surface by micrometeoroids and larger impactors over billions of years has created a layer of loose, fragmented material known as regolith. This layer covers much of the lunar surface and is several meters thick in some areas.

6. Tidal Evolution:

• The gravitational interactions between the Moon and Earth have led to tidal forces that influenced the Moon’s rotation. As a result, the same face of the Moon always points toward Earth in a phenomenon known as synchronous rotation.

7. Seismic Activity:

• While the Moon is not tectonically active like Earth, it does experience moonquakes. These quakes are thought to be caused by the gravitational interactions with Earth, the cooling and contraction of the Moon’s interior, or the stress induced by impacts.

8. Surface Weathering :

• The Moon’s lack of atmosphere means that it is not subject to weathering processes like wind and water erosion. However, micrometeoroid impacts and the solar wind have contributed to a form of “space weathering,” altering the surface properties over time.

9. Recent Geological Activity (Possible):

• Recent discoveries, including observations of transient lunar phenomena and hints of potential volcanic activity, have raised questions about the possibility of more recent geological processes. However, further research is needed to confirm the nature and extent of any recent lunar activity.

In summary, the Moon’s early history was shaped by intense bombardment during the Late Heavy Bombardment, followed by the formation of impact basins and volcanic activity that created the lunar maria. Over time, the Moon’s geological activity declined, and its surface was further modified by ongoing impact cratering and the accumulation of regolith. Studying the Moon’s geological history provides valuable insights into the early solar system and the processes that shaped rocky bodies in our cosmic neighborhood.

In conclusion, the formation of the Moon is intricately tied to the Giant Impact Hypothesis, which proposes that a massive collision between Earth and a Mars-sized protoplanet, Theia, led to the creation of our natural satellite. Key points in the Moon’s formation include:

• Giant Impact Hypothesis: The Moon formed approximately 4.5 billion years ago as a result of a colossal collision between Earth and Theia. The impact led to the ejection of debris, the formation of an accretion disk, and the gradual coalescence of material into the Moon.
• Composition and Isotopic Similarities: Moon rock samples collected during the Apollo missions exhibit a composition similar to Earth’s crust, supporting the hypothesis that the Moon originated from both Earth and Theia. Isotopic ratios further confirm these similarities.
• Accretion and Differentiation: The accretion of material within the proto-lunar disk, driven by gravitational forces, led to the differentiation of the Moon’s interior. The Moon’s crust, mantle, and limited core reflect the processes of early solar system evolution.
• Post-Formation Evolution: The Moon’s early history was marked by intense bombardment during the Late Heavy Bombardment, the formation of impact basins, and volcanic activity that created the lunar maria. Ongoing geological processes, such as regolith formation and tidal evolution, continue to shape the lunar surface.
• Scientific Interest and Exploration: The Moon remains a focal point for scientific interest and exploration. Ongoing missions, including robotic landers, orbiters, and potential crewed missions, aim to uncover new insights into lunar geology, the Moon’s history, and its potential as a platform for further space exploration.

The Moon serves as a natural laboratory for studying planetary processes, the early solar system, and the dynamics that have shaped rocky bodies in our cosmic neighborhood. Continued scientific exploration, including planned lunar missions and potential human presence, holds the promise of unraveling more mysteries about the Moon’s formation and evolution, as well as its significance in the broader context of space exploration and understanding our solar system.

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Structural stability hypothesis of dual unitary quantum chaos

Jonathon riddell, curt von keyserlingk, tomaž prosen, and bruno bertini, phys. rev. research 6 , 033226 – published 29 august 2024.

• No Citing Articles
• INTRODUCTION
• STABILITY OF THE ERGODIC PHASE…
• PERTURBATION THEORY
• DISCUSSION OF ASSUMPTION t2
• CONCLUSIONS
• ACKNOWLEDGMENTS

Having spectral correlations that, over small enough energy scales, are described by random matrix theory is regarded as the most general defining feature of quantum chaotic systems as it applies in the many-body setting and away from any semiclassical limit. Although this property is extremely difficult to prove analytically for generic many-body systems, a rigorous proof has been achieved for dual-unitary circuits—a special class of local quantum circuits that remain unitary upon swapping space and time. Here we consider the fate of this property when moving from dual-unitary to generic quantum circuits focusing on the spectral form factor , i.e., the Fourier transform of the two-point correlation. We begin with a numerical survey that, in agreement with previous studies, suggests that there exists a finite region in parameter space where dual-unitary physics is stable and spectral correlations are still described by random matrix theory, although up to a maximal quasienergy scale. To explain these findings, we develop a perturbative expansion: it recovers the random matrix theory predictions, provided the terms occurring in perturbation theory obey a relatively simple set of assumptions. We then provide numerical evidence and a heuristic analytical argument supporting these assumptions.

• Received 15 March 2024
• Accepted 30 July 2024

DOI: https://doi.org/10.1103/PhysRevResearch.6.033226

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

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• Research Areas
• Physical Systems

Authors & Affiliations

• 1 School of Physics and Astronomy, University of Nottingham , Nottingham NG7 2RD, United Kingdom
• 2 Centre for the Mathematics and Theoretical Physics of Quantum Non-Equilibrium Systems, University of Nottingham , Nottingham NG7 2RD, United Kingdom
• 3 Department of Physics, King's College London , Strand WC2R 2LS, United Kingdom
• 4 Faculty of Mathematics and Physics, University of Ljubljana , Jadranska 19, SI1000 Ljubljana, Slovenia
• 5 Institute of Mathematics, Physics, and Mechanics , Jadranska 19, SI1000 Ljubljana, Slovenia

Article Text

Vol. 6, Iss. 3 — August - October 2024

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• Quantum Physics
• Quantum Information

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Diagrammatic representation of tr [ U t ] . The boxes represent local gates and different legs act on different spatial sites. Matrix product is represented by joining legs and goes from bottom to top. The lines at the left and right edges are joined because we consider periodic boundary conditions ( L ≡ 0 ), while those at the top and bottom are joined because of the trace. The background grid specifies the space-time lattice. The gates in the same vertical column are identical.

Graphical representation of K ( t , L ) [cf. Eq. ( 11 )]. The symbols represent the local gates as per Eqs. ( 12 ) and ( 13 ). Random one-site gates along the same column coincide, while those on different columns are uncorrelated.

The gap Δ 0 ( t ) = 1 − | λ 1 | at the dual unitary point for various t and J , all data are collected from ( ν , ν ′ ) = ( 0 , 0 ) symmetry sector. The top plot takes α → ∞ as in Eq. ( 32 ) while the bottom plot sets J = 0 and takes σ finite. The bottom plot is the only data set in this article where σ is taken to be finite, all other datasets and figures take σ → ∞ . The data showcased in the top plot with J = 0 are featured in Fig.  9 .

ln ( λ 0 ( t ) − 1 ) as a function of time for various ε 1 , ε 2 . Dotted lines indicate numerical fits. Circle data points are retrieved with the power method isolated in the ( ν , ν ′ ) = ( 0 , 0 ) symmetry sector. Diamond data points are calculated using the Monte Carlo. Monte Carlo data consist of 10 7 samples for t ≤ 10 and t > 10 use 10 5 data points. In the top two panels, we supply exact values and Monte Carlo estimates for all times t , while in the bottom two panels, we simply plot exact values for t ≤ 9 and the remaining points are Monte Carlo estimations.

The gap Δ = | λ 0 | − | λ 1 | versus time t for various choices of perturbation. These data were retrieved using the Arnoldi method in the ( ν , ν ′ ) = ( 0 , 0 ) symmetry sector.

Full spectrum λ n , ( ν , ν ) analysis (all diagonal double momentum sectors) of T for various ε and t . Points are plotted in polar coordinates, with the radius being the magnitude of the eigenvalue (this plot therefore covers up some degeneracy in the sub-leading eigenvalues). The polar angle is 2 π ν / t , where ν labels the symmetry sector ( ν , ν ) . Results were obtained by an Arnoldi method converging n = 12 eigenvalues at the edge of the spectrum.

[ n ] terms in perturbation theory as a function of t and n . Solid dots represent the natural logarithm of data retrieved through exact evaluation of [ n ] in the ( ν , ν ′ ) = ( 0 , 0 ) sector. Dotted lines are numerical fits indicating exponential dependence on the independent variables t , n .

[ n ] terms in perturbation theory as a function of t and n . Solid dots represent the natural logarithm of data retrieved through exact evaluation of [ n ] in the ( ν , ν ′ ) = ( 0 , 0 ) sector. Dotted lines are numerical fits indicating an exponential dependence on the independent variables t , n .

Data extracted from numerical fits in Figs.  7 and 8 for different choices of ε 1 , ε 2 . α ( t , ε ) , δ ( t , ε ) correspond to the quantities defined in Eq. ( 75 ). Δ 0 ( t ) is the gap at the dual unitary point. Importantly we plot Δ 0 ( 9 ) for reference, α ( t , ε ) and δ ( t , ε ) were not extracted for t = 9 .

Diagrammatic representation of B n , 0 (a) and B n , τ ≠ 0 (b).

Flat coefficients [ 1 , 1 , 1 ⋯ 1 ] as a function of t for different values of m and ε . The top panels report two examples of case I ( ( ε 1 , ε 2 ) = ( 0.1 , 0 ) and ( ε 1 , ε 2 ) = ( 0.3 , 0 ) ) while the bottom ones report two examples of case II ( ε 1 = ε 2 = 0.01 and ε 1 = ε 2 = 0.1 ).

Flat coefficients [ 111 ⋯ 1 ] as a function of m for different values of t and ε . The top panels report two examples of case I ( ( ε 1 , ε 2 ) = ( 0.1 , 0 ) and ( ε 1 , ε 2 ) = ( 0.3 , 0 ) ) while the bottom ones report two examples of case II ( ε 1 = ε 2 = 0.01 and ε 1 = ε 2 = 0.1 ).

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