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Chapter: Foundations of Life Science
Lesson 1: Nature of Science
- List the principles that should guide scientific research.
- Examine a scientist’s view of the world.
- Outline a set of steps that might be used in the scientific method of investigating a problem.
- Explain why a control group is used in an experiment.
- Outline the role that reasoning plays in examining hypotheses.
- Examine the function of the independent variable in an experiment.
- Define what is meant by a theory.
- Compare a hypothesis to a theory.
The goal of science is to learn how nature works by observing the physical (natural) world, and to understand it through research and experimentation. It is a distinctive way of learning about the natural world.
Goals of Science [B-head]
Science involves objective, logical, and repeatable attempts to understand the principles and forces working in the natural universe. Science is from the Latin word, scientia, which means "knowledge." Good science is an ongoing process of testing and evaluation. One of the hoped-for benefits of students taking a biology course is that they will become more familiar with the process of science.
Humans are naturally interested in the world we live in. Young children constantly ask "why" questions. Science is a way to get some of those "whys" answered. When we shop for groceries, we are carrying out a kind of scientific experiment. If you like Brand X of salad dressing, and Brand Y is on sale, perhaps you try Brand Y. If you like Y you may buy it again even when it is not on sale. If you did not like Brand Y, then no sale will get you to try it again.
[Insert Figure 1, girl shopping, here]
There are many different areas of science, or scientific disciplines, but all scientific study involves:
- asking questions
- making observations
- relying on evidence to form conclusions
- being skeptical about ideas or results
Skepticism is a position in which a person questions the truthfulness of claims that lack evidence. Scientific skepticism (also called skeptical inquiry), questions claims based on their scientific verifiability rather than accepting claims on faith or anecdotes. Scientific skepticism uses critical thinking to analyze such claims and opposes claims which lack scientific evidence.
How Scientists Think [B-head]
The acronym CUDOS is a helpful way to remember the principles that should guide good scientific research. An acronym is an abbreviation, such as NATO, laser, and AIDS, that is formed by using the initial letters of words or word parts in a phrase or name. According to the CUDOS principles, scientific research should be governed by Communalism, Universalism, Disinterestedness, Originality, and Skepticism.
- Communalism means that scientific results are common property, to be shared with the entire scientific community.
- Universalism means that all scientists can contribute to science regardless of race, nationality, culture, or gender.
- Disinterestedness means that scientists should not present their results in a way that is affected by their personal beliefs or by their activism for a certain cause. Scientists should have a dispassionate attitude towards their findings. (Read more about disinterestedness later in the lesson under the topics of scientific bias and conflicts of interest).
- Originality means that claims made by researchers must be novel and add something to our knowledge and understanding of the world.
- Skepticism means that scientific claims must be exposed to scientific testing (through critical thinking) before being accepted.
This acronym was first developed in 1942 by a sociologist named Robert Merton. The term CUDOS is gaining in acceptance in the scientific community as a way of summarizing the principles for good science.
Even though the guiding principles can apply to all scientific research, scientists differ greatly from one another in what they investigate and in how they go about their work. For example, thy differ :
- in the reliance they have on historical data or on experimental data and findings.
- in what they measure, and how they measure it.
- in how much they use fundamental principles such as gravity, force, or atomic theory in their studies and research.
- in how much they draw on the findings of other sciences.
Still, scientists share certain basic beliefs and attitudes about what they do and how they view their work. These have to do with the nature of the world and what can be learned about it.
The exchange of techniques, information, and concepts between scientists goes on all the time. There are common understandings among scientists about what a scientific investigation is and what makes a claim scientifically valid.
A Scientific View of the World [C-head]
Science is based on the analysis of things that humans can observe either by themselves through their senses, or by using special equipment. Science therefore cannot explain anything about the natural world that is beyond what is observable by current means. The term supernatural refers to entities, events, or powers regarded as being beyond nature, in that such things cannot be explained by scientific means. They are not measurable or observable in the same way the natural world is, and so considered to be outside the realm of scientific examination.
When a natural occurrence which was once considered supernatural is understood in the terms of natural causes and consequences, it has a scientific explanation. For example, the flickering lights sometimes seen hovering over damp ground on still evenings or nights are commonly called Will-o’-the-wisp (in Western Europe, Eastern United States, and Eastern Canada). Will-o’-the-wisp looks like a lamp or flame, and is sometimes said to move away if approached. Much folklore surrounds the legend, such as the belief that the lights are lost souls, or fairies attempting to lead travelers astray. However, science has offered several potential explanations for Will-o’-the-wisp from burning marsh gases to glowing fungi or animals (who glow, or fluoresce in a similar way to lightning bugs).
There is no fixed set of steps that scientists always follow, nor is there one single path that leads to scientific knowledge. There are, however, certain features of science that give it a very specific way of investigating something. You do not have to be a professional scientist to think like a scientist. Everyone, including you, can use these features of scientific thinking to think critically about issues and situations in everyday life.
Science assumes that the universe is a vast single system in which the basic rules are the same. Things that are learned from studying one part of the universe can be applied to other parts of the universe. For example, the same principles of motion and gravitation that explain the motion of falling objects on Earth also explain the orbit of the planets around the sun, and galaxies, as shown in Figure 2.
[Insert Figure 2, solar system/Ferris wheel, here]
Nature Can be Understood
Science presumes that the things and events in the universe happen in patterns that can be understood by careful study. Scientists believe that through the use of the mind, and with the help of instruments that extend the human senses, people can discover patterns in all of nature that can help us understand the world and universe.
Scientific Ideas Can Change
Science is a process for developing knowledge. Change in knowledge about the natural world is expected because new observations may challenge the existing understanding of nature. No matter how well one theory explains a set of observations, it is possible that another theory may fit just as well or better, or may fit a still wider range of observations. In science, the testing and improving of theories goes on all the time. Scientists know that even if there is no way to gain complete knowledge about something, an increasingly accurate understanding of nature will develop over time.
The ability of scientists to make more accurate predictions about the natural world, from determining how a cancerous tumor develops a blood supply to calculating the orbit of an asteroid, provides evidence that scientists are gaining an understanding of how the world works.
Scientific Knowledge Can Stand the Test of Time
Continuity and stability are as much characteristics of science as change is. Although scientists accept some uncertainty as part of nature, most scientific knowledge stands the test of time. A changing of ideas, rather than a complete rejection of the ideas, is normal practice in science. Powerful ideas about nature tend to survive, grow more accurate and become widely accepted.
For example, in developing the theory of relativity, Albert Einstein did not throw out Issac Newton’s laws of motion but rather, he showed them to be only a small part of the bigger, cosmic picture. That is, the Newtonian laws of motion have limited use within a more general concept (the universe). For example, the National Aeronautics and Space Administration (NASA) uses the Newtonian laws of motion to calculate the flight paths of satellites and space vehicles.
Science Cannot Offer Answers to All Questions
There are many things that cannot be examined in a scientific way. There are, for instance, beliefs that cannot be proved or disproved (such as the existence of supernatural powers, supernatural beings, or the meaning of life). In other cases, a scientific approach to a question and a scientific answer may be rejected by people who hold to certain beliefs.
Scientists do not have the means to settle questions about things such as good and evil, or love and hate, although they can sometimes contribute to the discussion of such issues by identifying the likely reasons for certain actions by humans, and possible consequences of these actions. The contributions of science may be helpful in understanding such topics.
Scientific Methods [B-head]
Science attempts to understand nature. It can be difficult sometimes to define research methods in a way that will clearly distinguish science from non-science. However, there is a set of core principles that make up the "bones" of scientific research. These principles are accepted within the scientific community and among academics such as philosophers of science.
We learned earlier in this lesson that there is no fixed set of steps that scientists always follow during an investigation. Neither is there one single path that leads scientists to knowledge. There are, however, certain features of science that give it a very specific way of investigating things.
Scientific investigations examine, gain new knowledge, or build on previous knowledge about phenomena. A phenomenon, is any occurrence that is observable, such as the burning match shown in Figure 3. A phenomenon may be a feature of matter, energy, or time. For example, Isaac Newton made observations of the phenomenon of the moon’s orbit. Galileo Galilei made observations of phenomena related to swinging pendulums.
[Insert Figure 3, match lighting, here]
Although procedures vary from one field of scientific inquiry to another, certain features distinguish scientific inquiry from other types of knowledge. Scientific methods are based on gathering observable, empirical (produced by experiment or observation) and measurable evidence that is critically evaluated.
A hypothesis is a suggested explanation based on evidence that can be tested by observation or experimentation. Experimenters may test and reject several hypotheses before solving a problem.
Scientific Investigations [C head]
The scientific method is not a step by step, linear process. It is a way of learning about the world through the application of knowledge. Scientists must be able to have an idea of what the answer to an investigation is. Scientists will often observe and then form a hypothesis to explain why a phenomenon occurred. They use all of their knowledge and a bit of imagination in their journey of discovery.
Scientific investigations involve the collection of data through observation, the formation and testing of hypotheses by experimentation, and analysis of the results that involves reasoning.
Scientific investigations begin with observations that lead to questions. We will use an everyday example to show what makes up a scientific investigation. Imagine that you walk into a room, and the room is dark.
- You observe that the room appears dark, and you question why the room is dark.
- In an attempt to find explanations to this phenomenon, you develop several different hypotheses. One hypothesis might state that the room does not have a light source at all. Another hypothesis might be that the lights are turned off. Still, another might be that the light bulb has burnt out. Worst yet, you could be going blind.
- To discover the answer, you experiment. You feel your way around the room and find a light switch and turn it on. No light. You repeat the experiment, flicking the switch back and forth; still nothing.
- This means your first two hypotheses, that the room is dark because (1) it does not have a light source; and (2) the lights are off, have been rejected.
- You think of more experiments to test your hypotheses, such as switching on a flashlight to prove that you are not blind.
- In order to accept your last remaining hypothesis as the answer, you could predict that changing the light bulb will fix the problem. If your predictions about this hypothesis succeed (changing the light bulb fixes the problem), the original hypothesis is valid and is accepted.
- However, in some cases, your predictions will not succeed (changing the light bulb does not fix the problem), and you will have to start over again with a new hypothesis. Perhaps there is a short circuit somewhere in the house, or the power might be out.
The general process of a scientific investigation is summed up in Figure 4.
[Insert Figure 4, scientific investigation, here]
|Table 1 Common Terms used in Scientific Investigations|
|Scientific Method||The process of scientific investigation|
|Observation||The act of noting or detecting phenomenon by the senses. For example, taking measurements.|
|Hypotheses||A suggested explanation based on evidence that can be tested by observation or experimentation|
|Scientific Reasoning||The process of looking for scientific reasons for observations|
|Experiment||A test that is used to rule out a hypothesis or validate something already known.|
|Rejected Hypothesis||An explanation that is ruled out by experimentation|
|Confirmed Hypothesis||An explanation that is not ruled out by repeated experimentation and makes predictions that are shown to be true.|
|Inference||Developing new knowledge based upon old knowledge.|
|Theory||A widely accepted hypothesis that stands the test of time. Often tested, and usually not rejected.|
Scientists first make observations that raise questions. An observation is the act of noting or detecting phenomenon through the senses. For example, noting that a room is dark, or counting the number of birds that visit a bird feeder.
In order to explain the observed phenomenon, scientists develop a number of possible explanations, or hypotheses. A hypothesis is a suggested explanation for a phenomenon or a suggested explanation for a relationship between many phenomena. Hypotheses are always based on evidence that can be tested by observation or experimentation.
Scientific investigations are required to test hypotheses. Scientists mostly base hypotheses on prior observations or on extensions of existing scientific explanations.
A hypothesis is not really an educated guess. To define a hypothesis as "an educated guess" is like calling a tricycle a "vehicle with three". The definition leaves out the concept’s most important and characteristic feature: the purpose of hypotheses. People generate hypotheses as early attempts to explain patterns observed in nature or to predict the outcomes of experiments. For example, in science, one could correctly call the following statement a hypothesis: identical twins can have different personalities because the environment influences personality.
Scientific methods require hypotheses that are falsifiable, that is, they must be framed in a way that allows other scientists to prove them false. Proving a hypothesis to be false is usually done by observation. However, confirming (or failing to falsify) a hypothesis does not necessarily mean the hypothesis is true.
For example, a person comes to a new country and sees (observes) only white sheep. This person might form the hypothesis: "All sheep in this country are white." This statement can be called a hypothesis, because it is falsifiable; anyone could falsify the hypothesis by observing a single black sheep, shown in Figure 5. If the experimental uncertainties remain small (for example, that a person can reliably tell the observed black sheep from a goat or a small horse), and if the experimenter has correctly interpreted the hypothesis (for example, does the meaning of "sheep" include male sheep (rams), or just female sheep (ewes)?), finding a black sheep falsifies the "only white sheep" hypothesis. However, you cannot call a failure to find non-white sheep as proof that no non-white sheep exist.
[Insert Figure 5, sheep, here]
Scientific Reasoning [B-head]
Any useful hypothesis will allow predictions based on reasoning. Reasoning can be broken down into two categories: deduction and induction. Most reasoning in science is done through induction.
Deductive Reasoning (Deduction) [C-head]
Definition: Determining a single fact from a general statement; it is only as accurate as the statement.
Example: The teacher said she checks homework every Monday; therefore she will check homework on next Monday.
Deductions are intended to have reasoning that is valid. The reasoning in this argument is valid, because there is no way in which the reasons 1 and 2, could be true and the conclusion, 3, be false:
Reason 1: All humans are mortal.
Reason 2: Albert Einstein is a human.
Conclusion: Albert Einstein is mortal.
[Insert Figure 6, Albert Einstein, here]
Inductive Reasoning (Induction) [C-head]
Definition: Determining a general statement from several facts that is very likely to be true.
Example: We have had a test every Tuesday for the past three months; therefore, we will have a test next Tuesday (and every Tuesday).
Induction contrasts strongly with deduction. Even in the best, or strongest, cases of induction, the truth of the reason does not guarantee the truth of the conclusion. Instead, the conclusion of an inductive argument is very likely to be true; you cannot be fully sure it is true because you are making a prediction that has yet to happen.
A classical example of inductive reasoning comes from the philosopher David Hume:
Reason: The sun has risen in the east every morning up until now.
Conclusion: The sun will also rise in the east tomorrow.
Inductive reasoning involves reaching conclusions about unobserved things on the basis of what has been observed already. Inferences about the past from present evidence, such as in archaeology, are induction. Induction could also be across outer space, as in astronomy where conclusions about the whole universe are drawn from the limited number of things we are able to observe.
Experiments [B head]
A scientific experiment must have the following features:
- a control, so variables that could affect the outcome are reduced
- the variable being tested reflects the phenomenon being studied
- the variable can be measured accurately, to avoid experimental error
- the experiment must be reproducible
An experiment is a test that is used to eliminate one of more of the possible hypotheses until one hypothesis remains. The experiment is a cornerstone in the scientific approach to getting deeper knowledge about the physical world. Scientists use the principles of their hypothesis to make predictions, and then test to see if their predictions are confirmed or rejected.
Scientific experiments involve controls, or subjects that are not tested during the investigation. In this way, a scientist limits the factors, or variables that can cause the results of an investigation to differ. A variable is a factor that can change over the course of an experiment. Independent variables are factors whose values are controlled by the experimenter to determine its relationship to an observed phenomenon (the dependent variable).Dependent variables change in response to the independent variable. Controlled variables are also important to identify in experiments. They are the variables that are kept constant to prevent them from influencing the effect of the independent variable on the dependent variable.
For example, if you were to measure the effect that different amounts of fertilizer have on plant growth, the independent variable would be the amount of fertilizer used (the changing factor of the experiment). The dependent variables would be the growth in height and/or mass of the plant (the factors that are influenced in the experiment). The controlled variables include the type of plant, the type of fertilizer, the amount of sunlight the plant gets, the size of the pots you use. The controlled variables are controlled by you, otherwise they would influence the dependent variable.
- The independent variable answers the question "What do I change?"
- The dependent variables answer the question "What do I observe?"
- The controlled variables answer the question "What do I keep the same?"
Experimental Design [C-head]
In the old joke, a person claims that they are snapping their fingers "To keep tigers away"; and justifies their behavior by saying "See, it works!" While this "experiment" does not falsify the hypothesis "Snapping your fingers keeps tigers away," it does not support the hypothesis either, because not snapping your fingers will also keeps tigers away. It also follows that not snapping your fingers will not cause tigers to suddenly appear.
[Insert Figure 7, tiger, here]
To demonstrate a cause and effect hypothesis, an experiment must often show that, for example, a phenomenon occurs after a certain treatment is given to a subject, and that the phenomenon does not occur in the absence of the treatment.
One way of finding this out is to carry out a controlled experiment. In a controlled experiment, two identical experiments are carried out side-by-side. In one of the experiments the independent variable being tested is used, in the other, the control, the independent variable is not used.
A controlled experiment generally compares the results obtained from an experimental sample against a control sample. The control sample is almost identical to the experimental sample except for the one variable whose effect is being tested. A good example would be a drug trial. The sample or group receiving the drug would be the experimental group, and the group receiving the placebo would be the control. A placebo, is a form of "medicine" that does not contain the drug that is being tested.
Controlled experiments can be carried out when it is difficult to exactly control all the conditions in an experiment. In this case, the experiment begins by creating two or more sample groups that are similar in as many ways as possible, which means that both groups should respond in the same way if given the same treatment.
Once the groups have been formed, the experimenter tries to treat them identically except for the one variable that he or she wants to study (the independent variable). Usually neither the patients nor the doctor know which group receives the real drug, which serves to isolate the effects of the drug and allow the researchers to be sure the drug does work, and that the effects seen in the patient is not due to the patient believing they are getting better. This type of experiment is called a double blind experiment.
Controlled experiments can be carried out on many more things other than people, some are even carried out in space! The wheat plants in Figure 8 are being grown in the International Space Station to study the effects of microgravity on plant growth. Researchers hope that one day enough plants could be grown aboard during spaceflight to feed hungry astronauts and cosmonauts. The investigation also measured the amount of oxygen the plants can produce in the hope that plants could become a cheap and effective way to provide oxygen during space travel.
[Insert Figure 8, space wheat, here]
Experiments Without Controls
The term experiment usually means a controlled experiment, but sometimes controlled experiments are difficult or impossible to do. In this case researchers carry out natural experiments. Natural experiments depend on the scientist’s observations of the system under study, rather than controlling just one or a few variables as happens in controlled experiments.
For a natural experiment, researchers attempt to collect data in such a way that the effects of all the variables can be determined, and where the effects of the variation remains fairly constant so that the effects of other factors can be determined. Natural experiments are a common research tool in areas of study where controlled experiments are difficult to carry out. For example, astronomy (the study of stars, planets, comets, galaxies and phenomena that originate outside Earth’s atmosphere), paleontology (the study of prehistoric life forms through the examination of fossils), and meterology (the study of Earth’s atmosphere).
In astronomy it is impossible, when testing the hypothesis "Suns are collapsed clouds of hydrogen", to start out with a giant cloud of hydrogen, and then carry out the experiment of waiting a few billion years for it to form a sun. However, by observing various clouds of hydrogen in various states of collapse, and other phenomena related to the hypothesis, such as the nebula shown in Figure 9, researchers can collect data they need to support (or maybe falsify) the hypothesis.
An early example of this type of experiment was the first verification in the 1600s that light does not travel from place to place instantaneously, but instead has a speed that can be measured. Observation of the appearance of the moons of Jupiter were slightly delayed when Jupiter was farther from Earth, as opposed to when Jupiter was closer to Earth; and this phenomenon was used to demonstrate that the difference in the time of appearance of the moons was consistent with a measurable speed of light.
[Insert Figure 9, Helix nebula, here]
There are situations where it would be wrong or harmful to carry out an experiment. In these cases, scientists carry out a natural experiment. For example, alcohol can cause developmental defects in fetuses, leading to mental and physical problems, a condition called fetal alcohol syndrome.
Certain researchers want to study the effects of alcohol on fetal development but the researchers would not ask a group of pregnant women to drink alcohol to study its effects on their children. To do so would be considered wrong, or unethical. Instead, researchers carry out a natural experiment in which they study data that is gathered from mothers of children with fetal alcohol syndrome, or pregnant women who continue to drink alcohol during pregnancy. The researchers will try to reduce the number of variables in the study (such as the amount or type of alcohol consumed), which might affect their data. It is important to note that the researchers do not influence or encourage the consumption of alcohol, they collect this information from volunteers. This is one of the reasons why most health professionals recommend that pregnant women avoid alcohol completely.
Field experiments are so named to distinguish them from lab experiments. Field experiments have the advantage that observations are made in a natural setting rather than in a human-made laboratory environment. However, like natural experiments, field experiments can get contaminated, and conditions like the weather are not easy to control. Experimental conditions can be controlled with more precision and certainty in the lab.
A prediction is a statement that tells what will happen under specific conditions. It can be expressed in the form: If A is true, then B will also be true. Predictions are based on confirmed hypotheses (shown to be true or not proved to be false).
For a researcher to be confident that his or her predictions will be useful and descriptive, their data must have as few errors as possible. Accuracy is the measure of how close a calculated or measured quantity to its actual (true) value. Accuracy is closely related to precision, also called reproducibility or repeatability. Reproducibility and repeatability of experiments are cornerstones of scientific methods. If no other researchers can reproduce or repeat the results of a certain study, then the results of the study will not accepted as valid. Result are called valid only if it they are both accurate and precise.
A useful tool to help explain the difference between accuracy and precision is a target, shown in Figure 10. In this analogy, repeated measurements are the arrows that are fired at a target. Accuracy describes the closeness of arrows to the bulls eye at the center. Arrows that hit closer to the bulls eye are more accurate. Arrows that are grouped together more tightly are more precise.
[Insert Figure 10, targets, here]
Experimental Error [C-head]
An error is a boundary on the precision and accuracy of the result of a measurement. Some errors are caused by unpredictable changes in the measuring devices (such as balances, rulers, or calipers), but other errors can be caused by reading a measuring device incorrectly or by using broken or malfunctioning equipment. Such errors can have an impact on the reliability of the experiment’s results; they affect the accuracy of measurements. For example, you use weighing scales to weigh a 100 gram block. Three measurements that you get are: 93.1 g, 92.0 g, and 91.8 g. The measurements are precise, as they are close together, but they are not accurate.
If the cause of the error can be identified, then it can usually be cut out or minimized. Reducing the number of possible errors by careful measurement and using a large enough sample size to reduce the effect of errors will improve the reliability of your results.
Scientific Theories [B-head]
Scientific theories are hypotheses which have stood up to repeated attempts at falsification and are thus supported by much data and evidence. Some well known biological theories include the theory of evolution by natural selection, the cell theory (the idea that all organisms are made of cells), and the germ theory of disease (the idea that certain microbes cause certain diseases). The scientific community holds that much more evidence supports these ideas than contradicts them, and so they are referred to as theories.
In every day use, people often use the word theory to describe a guess or an opinion. For example, "I have a theory as to why the light bulb is not working." When used in this common way, "theory" does not have to be based on facts, it does not have to be based on a true description of reality. This usage of the word theory often leads to a misconception that can be best summed up by the phrase "It’s not a fact, it’s only a theory." In such everyday usage, the word is most similar to the term hypothesis.
Scientific theories are the equivalent of what everyday in everyday speech we would refers to as facts. In principle, scientific theories are always subject to corrections or inclusion in another, wider theory. As a general rule for use of the term, theories tend to deal with much broader sets of phenomena than do hypotheses, which usually deal with a much more specific sets of phenomena or a specific applications of a theory.
In time, a confirmed hypothesis may become part of a theory or may grow to become a theory itself. Scientific hypotheses may be mathematical models. Sometimes, they can be statements, stating that some particular instance of the phenomenon under examination has some characteristic and causal explanations. These theories have the general form of universal statements, stating that every instance of the phenomenon has a particular characteristic.
A hypothesis may predict the outcome of an experiment in a laboratory or the observation of a natural phenomenon. A hypothesis should also be falsifiable, and one cannot regard a hypthesis or a theory as scientific if it does not lend itself to being falsified, even in the future. To meet the "falsifiable" requirement, it must at least in principle be possible to make an observation that would disprove the hypothesis. A falsifiable hypothesis can greatly simplify the process of testing to determine whether the hypothesis can be proven to be false. Scientific methods rely heavily on the falsifiability of hypotheses by experimentation and observation in order to answer questions. Philosopher Karl Popper suggested that all scientific theories should be falsifiable otherwise they could not be tested by experiment.
A scientific theory must meet the following requirements:
- is consistent with pre-existing theory in that the pre-existing theory was experimentally verified, though it will often show a pre-existing theory to be wrong in an exact sense
- is supported by many strands of evidence rather than a single foundation, ensuring that it is probably a good approximation, if not totally correct.
Also, a theory is generally only taken seriously if it:
- allows for changes to be made as new data is discovered, rather than claiming certainty.
- is the most straight forward explanation; it makes the fewest assumptions about a phenomenon (commonly called "passing the Occam’s razor test").
This is true of such established theories as special relativity, general relativity, quantum mechanics, plate tectonics, and evolution. Theories considered scientific meet at least most, but ideally all, of these extra criteria.
You can sum up all of this by saying that to meet the status of a scientific theory, the theory must be falsifiable or testable. Examples of scientific theories in different areas of science include:
- Astronomy: Big Bang Theory
- Biology: Cell Theory; Theory of Evolution; Germ Theory of Disease
- Chemistry: Atomic Theory; Kinetic Theory of Gases
- Physics: General Relativity; Special Relativity; Theory of Relativity; Quantum Field Theory
- Earth Science: Giant Impact Theory; Plate Tectonics
Currently Unverifiable Theories
The term theory is sometimes stretched to refer to theoretical speculation which is currently unverifiable. Examples are string theory and various theories of everything. String theory is a model of physics, which predicts the existence of many more dimensions in the universe than the four dimensions that current science understands (length, width, height, and space-time). A theory of everything is a hypothetical theory in physics that fully explains and links together all known physical phenomena.
For a scientific theory to be valid it must be verified experimentally. Many parts of the string theory are currently untestable due to the large amount of energy that would be needed to carry out experiments and the high cost of them. Therefore string theory may not be tested in the foreseeable future, so some scientists have asked if it even deserves to be called a scientific theory because it is not falsifiable.
A superseded, or obsolete, scientific theory is a theory that was once commonly accepted but (for whatever reason) is no longer considered the most complete description of reality by mainstream science. It can also mean a falsifiable theory which has been shown to be false.
In some cases, the theory has been completely discarded. In other cases, the theory is still useful because it provides a description that is "good enough" for a particular situation. Giraffes, shown in Figure 11, are often used in the explanation of Lamarck’s superseded theory of evolution. In Lamarckism, a giraffe is able to lengthen its neck over its life time, for example by stretching to reach higher leaves. That giraffe will then have offspring with longer necks. The theory has been superseded by the understanding of natural selection on populations of organisms as the main means of evolution, not physical changes to a single organism over its lifetime.
[Insert Figure 11, giraffes, here]
Scientific laws are similar to scientific theories in that they are principles which can be used to predict the behavior of the natural world. Both scientific laws and scientific theories are typically well-supported by observations and/or experimental evidence. Usually scientific laws refer to rules for how nature will behave under certain conditions. Scientific theories are more overarching explanations of how nature works and why it exhibits certain characteristics.
A physical law or law of nature is a scientific generalization based on a sufficiently large number of empirical observations that it is taken as fully verified.
Isaac Newton’s law of gravitation is a famous example of an established law that was later found not to be universal—it does not hold in experiments involving motion at speeds close to the speed of light or in close proximity of strong gravitational fields. Outside these conditions, Newton’s Laws remain an excellent model of motion and gravity.
Scientists never claim absolute knowledge of nature or the behavior of the subject of the field of study. A scientific theory is always open to falsification, if new evidence is presented. Even the most basic and fundamental theories may turn out to be imperfect if new observations are inconsistent with them. Critical to this process is making every relevant part of research publicly available. This can allows peer review of published results, and it also allows ongoing reviews and repeats of experiments and observations by many different researchers. Only by meeting these expectations can it be said how reliable the experimental results are for possible use by others.
Lesson 1 Summary
- Scientific skepticism questions claims based on their scientific verifiability rather than accepting claims on faith or anecdotes. Scientific skepticism uses critical thinking to analyze such claims and opposes claims which lack scientific evidence.
- Science is based on the analysis of things that humans can observe either by themselves through their senses, or by using special equipment. Science therefore cannot explain anything about the natural world that is beyond what is observable by current means. Supernatural things cannot be explained by scientific means.
- Scientific investigations involve the collection of data through observation, the formation and testing of hypotheses by experimentation, and analysis of the results that involves reasoning.
- In a controlled experiment, two identical experiments are carried out side-by-side. In one of the experiments the independent variable being tested is used, in the other, the control, the independent variable is not used.
- Any useful hypothesis will allow predictions based on reasoning. Reasoning can be broken down into two categories: deduction and induction. Most reasoning in science is done through induction.
- A variable is a factor that can change over the course of an experiment. Independent variables are factors whose values are controlled by the experimenter to determine its relationship to an observed phenomenon (the dependent variable).Dependent variables change in response to the independent variable..
- Scientific theories are hypotheses which have stood up to repeated attempts at falsification and are thus supported by much data and evidence.
Points to Consider
Science is a one particular way in which people examine and ask questions about the world. Can you think of other ways in which people examine and ask questions about the world?
Consider the importance of replication in an experiment, and how replication of an experiment can affect results.
Scientists often disagree amongst themselves about scientific findings, and communicate such disagreement at science conferences, through science articles in magazines, or science papers, in scientific journals. Can you think of other ways in which scientists could communicate so that the public can a better idea what the "hot topics" in science are.
References: Foundations of Life Science
URLs of Interest
The first scientific experiment
Cinema and Science: http://www.cisci.net/about.php?lang=1
What is the goal of science?
goal of science is to learn how nature works by observing the physical (natural) world, and to understand it through research and experimentation.
Distinguish between a hypothesis and a theory.
A hypothesis is a suggested explanation based on evidence that can be tested by observation or experimentation. A theory is a widely accepted hypothesis that withstands repeated attempts at falsification.
The makers of two types of plant fertilizers claim that their product grows plants the fastest and largest. Design an experiment that you could carry out to investigate the claims.
Accept any reasonable design that follows scientific methods.
Identify how hypotheses and predictions are related.
Predictions are based on confirmed hypotheses.
What is the difference between the everyday term "theory" and the term "scientific theory"?
In every day use, people often use the word theory to describe a guess or an opinion. Scientific theories are hypotheses which have stood up to repeated attempts at falsification.
Identify two ways that scientists can test hypotheses.
Any two of the following: By carrying out a controlled experiment, a field experiment, or an investigation without an experiment.
Outline the difference between inductive and deductive reasoning.
Induction contrasts strongly with deduction. Inductive reasoning involves reaching conclusions about unobserved things on the basis of what has been observed already. Deduction on the other hand, is determining a single fact from a general statement. It is only as accurate as the statement, but it is based on things that are observed directly.
What is the range of processes that scientists use to carry out a scientific investigation called?
They are called scientific methods.
What role does skeptical thinking play in scientific investigations?
Scientific skepticism uses critical thinking to analyze claims and opposes claims which lack scientific evidence.
To ensure that your results are not due to chance, scientists will usually carry out an experiment a number of times, a process called replication. A scientist has two types of plants, A and B. She has about 40 plants of each type. She wants to test which plant produces the most oxygen under sunny conditions outdoors. Which approach to replication of the experiment do you think would be the most practical for her?
Testing several samples of plants A and B at the same time
Testing one sample of plant A and plant B in each experiment, over 40 days.
Testing several samples of the plants at one time will allow the scientist to replicate the experiment in a short period of time. If she were to carry out the experiment over many days, the weather might change which would affect the variables in the experiment.
In taking measurements, what is the difference between accuracy and precision?
Accuracy is the measure of how close a calculated or measured quantity to its actual (true) value. Precision, also called reproducibility or repeatability is closely related to accuracy.
Name two features that a hypothesis must have to be called a scientific hypothesis.
Reproducibility and falsifiability
Identify two features that a theory must have to qualify as a scientific theory.
The theory must be consistent with pre-existing theory that was experimentally verified, and it is supported by many strands of evidence rather than a single finding.
Give an example of a superceded theory.
Can a hypothesis take the form of a question? Explain your answer.
A hypothesis is a suggested explanation based on evidence that can be tested by observation or experimentation. So, a hypothesis cannot be a question.
Why is it a good idea to try to reduce the chances of errors happening in an experiment.
Errors will affect measurements, observations, and eventually experimental results, which would affect conclusions.
Observation: Flies are often found on or around stored raw meat.
Conclusion: Flies come from rotting meat.
The above observation and conclusion form the basis of the spontaneous generation of life, a belief that living organisms came directly from non-living things such as meat, mud, or straw.
Design an experiment that will investigate whether flies do indeed come directly from raw meat. Present your experimental design to your class.
Lesson 1 Figures
Figure 1 Shopping sometimes involves a little science experimentation. You are interested in inventing a new type of salad that you can pack for lunch. You might buy a vegetable or salad dressing that you have not eaten before, to discover if you like it. If you like it, you will probably buy it again. [Source: http://www.flickr.com/photos/johnjoh/463607020/. Photo by: star5112. Licence: CC-by-SA]
Figure 2 With some changes over the years, similar principles of motion have applied to different situations. The same scientific principles that help explain planetary orbits can be applied to the movement of a Ferris wheel. [Source: http://commons.wikimedia.org/wiki/Image:Solar_sys.jpg. Image by: NASA. Licence: PD; Ferris Wheel source: http://www.flickr.com/photos/pjlewis/53056038/. Image by: PJLewis. Licence: CC-by-SA]
[ click me!]
Figure 3 The combustion of this match is an observable event and therefore a phenomenon.
[Source: http://en.wikipedia.org/wiki/Image:Streichholz.jpg, Photo by: Sebastian Ritter. Licence: CC –by-SA 2.5]
Figure 4 The general process of scientific investigations. A diagram that illustrates how scientific investigation moves from observation of phenomenon to a theory. The progress is not as straightforward as it looks in this diagram. Many times, every hypothesis is falsified which means the investigator will have to start over again. [Source: http://en.wikibooks.org/wiki/Image:Ap_biology_scienceofbiology01.jpg. Image by: Cnelson. Licence: PD]
Figure 5 The statement "there are only white sheep in this country" is a scientific hypothesis because it is open to being falsified. However, a failure to see a black sheep will not falsify the hypothesis. [Cropped by writer from source: http://commons.wikimedia.org/wiki/Image:Schapen_33.jpg, Photo by: Fruggo. CC-by 1.0]
Figure 6 Albert Einstein (1879–1955) Deductive reasoning has helped us determine that Albert Einstein is a mortal being. [Source: http://commons.wikimedia.org/wiki/Image:Albert_Einstein_1947a.jpg. Image by: Oren Jack Turner, Princeton, N.J. - Modified with Photoshop by en:User: PM_Poon and later by User:Dantadd. Licence: PD
'Figure 7 Are tigers really scared of snapping fingers, or is it more likely they are just not found in your neighborhood?' Considering which of the hypotheses is more likely to be true can help you arrive at a valid answer. This principle, called Occam’s razor states that the explanation for a phenomenon should make as few assumptions as possible. In this case, the hypothesis "There are no tigers in my neighborhood to begin with" is more likely, because it makes the least number of assumptions about the situation. http://en.wikibooks.org/wiki/Image:Siberian_Tiger_by_Malene_Th.jpg. Photo by: Malene Thyssen. Licence: GFDL. ]
[Review: Is this a valid analogy? Or have I just created more confusion?--NGW]
Figure 8 Spaceflight participant Anousheh Ansari holds a miniature wheat plant grown in the Zvezda Service Module of the International Space Station. [Source: http://commons.wikimedia.org/wiki/Image:Anousheh_Ansari_in_the_ISS.jpg. Image by: NASA. Licence: PD]
[Review: Ansari is not part of the crew, she is a space tourist. However, this is such a great photo because it had a person in it!---NGW]
Figure 9 The Helix nebula, located about 700 light-years away in the constellation Aquarius, belongs to a class of objects called planetary nebulae. Planetary nebulae are the remains of stars that once looked a lot like our sun. When sun-like stars die, they puff out their outer gaseous layers. These layers are heated by the hot core of the dead star, called a white dwarf, and shine with infrared and visible colors. Scientists can study the birth and death of stars by analyzing the types of light that are emitted from nebulae. [Source: http://commons.wikimedia.org/wiki/Image:169141main_piaa09178.jpg, Licence: NASA/JPL-Caltech/Univ. of Ariz. Licence: PD]
Figure 10 A visual analogy of accuracy and precision. Left target: High accuracy but low precision; Right target: low accuracy but high precision. The results of calculations or a measurement can be accurate but not precise; precise but not accurate; neither accurate nor precise; or accurate and precise. [Source: http://en.wikipedia.org/wiki/Image:High_accuracy_Low_precision.svg, Licence: PD; Source: http://en.wikipedia.org/wiki/Image:High_precision_Low_accuracy.svg.
Figure 11 Natural selection is the process by which favorable traits that are heritable become more common in successive generations of a population of reproducing organisms, and unfavorable traits that are heritable become less common. Natural selection acts on the phenotype, or the observable characteristics of an organism, such that individuals with favorable phenotypes are more likely to survive and reproduce than those with less favorable phenotypes. [Source: http://commons.wikimedia.org/wiki/Image:Giraffes_Arusha_Tanzania.jpg. Photo by: Geir Kiste. Licence: GFDL]