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In this lesson, you will review what science encompasses and how it works, and cover some of the diversity of its fields. You will also review scientific ethics, reliability, techniques, evaluations, and theories.
The word science comes from a Latin word that means “to know.” However, science is more than just a collection of facts and knowledge. It is a way of observing nature and the universe, and of testing explanations for how and why things are the way they are. Scientists search for the truth. They strive to uncover facts and a better understanding of the natural world and how its parts are interrelated.
Scientific knowledge and understanding are built on the principle that the universe can be explained in terms of cause and effect. Although there are many definitions of science, only two are useful in our modern understanding: empiricism and realism.
According to empirical philosophy, scientific theories are objective, testable, and predictive of results that can be replicated and verified through experimentation. On the other hand, scientific realism is more akin to identifying objects and processes; their causes, constituents, or origins; and the manner in which the causes or origins work. In short, empiricism is more about asking questions about reality, and realism is more about identifying structure and cause. It may seem to be a subtle difference and the two are linked closely in a real-world definition of science that encompasses much of both schools of philosophy.
An important philosopher of science, Karl Popper, argued that in true scientific investigation, verification is impossible, and that advancements in scientific knowledge can only be made based on hypotheses that are held to be true, meaning they have not been falsified. Thomas Kuhn also stated that human bias makes all observations tainted with preconceptions based on the current paradigm. Kuhn argued that science involves paradigms and assumptions, and that scientific progress is mainly gained through the falsification or modification of paradigms and the emergence of newer and more powerful paradigms in a cycle that never ends. He also pointed out that science has never historically proceeded as a steady accumulation of facts, but as a series of dramatic (and sometimes cataclysmic) paradigm shifts that precipitate scientific revolution.
The universe works on a consistent set of principles that science attempts to summarize, organize, and interpret for use by man. For instance, storms occur because a certain amount of energy from the sun has heated parts of Earth more than others. Energy flows between these places in a predictable way that follows natural laws. This flow of energy causes the storm and other atmospheric phenomena. Almost every part of our daily lives is based on scientific knowledge and its applications.
Science covers a lot of conceptual ground; therefore, people separate it into different branches of knowledge. The term “branches” might indicate that the fields of science can be shown in a tree-like diagram. However, as our storehouses of knowledge expand, a web of knowledge may display science more accurately. No matter how you prefer to visualize the complexity of science, please realize that all of scientific progress is inter-related and there are no isolated disciplines within science—everything is connected.
Broad fields of scientific study include:
Most scientific investigations do not fall strictly within just one of these fields, and there is tremendous overlap and interconnection between them. Within and between these broad fields, there are many other classifications of science. These include biochemistry and geophysics, which combine concepts included in two or more of the broad fields. Others, for example botany and organic chemistry, are specialties within one of the broad fields. In addition, the principles of science are used by sociologists, economists, psychologists, and others who study human behavior. The main idea to remember is that science is a process that encompasses the whole range of causes and effects in the natural world and our systematic attempts to understand it all.
Science is a process that involves performing many different functions. Although many scientists work in laboratories, certain branches of science work mostly in the field. The settings for scientific research are often as diverse as the careers that utilize them. For instance, engineers, teachers, computer scientists, doctors, farmers, and even chefs do science every day. Furthermore, some scientific fields, such as astronomy, actively encourage amateur observers to contribute their data, observations, and interpretations to a larger bank of data for use by all astronomers. The bottom-line is that anyone, at any time, can think like a scientist.
Scientific research has several purposes. In its most basic form, science is a search for truth that leads to greater understanding. By nature, some people are curious about how things work, such as why the sky is blue, or whether it will rain tomorrow. Science also has a practical aspect, known as technology. Technology is the application of scientific knowledge to solve practical problems. Farmers use a wide variety of technologies to produce food. After early farmers observed that certain seeds grew better when the soil was loosened, they applied this knowledge to the design of the plow. Modern farm equipment now includes global positioning systems to help control precise application of fertilizer, water, and pesticides.
Modern technologies are built on the results of past scientific research that have occurred over many thousands of years. Think about all of the knowledge that goes into building your car, for example. The engine requires an understanding of the chemistry of fuel combustion and of the materials that can handle the heat generated by internal combustion. Brakes are designed to distribute massive forces of a thousand kilogram body moving at high speeds. Safety systems apply the results of biological investigations to prevent damage to human bodies in an accident. Even the process of designing an appealing shape applies the scientific study of aerodynamics and human aesthetics.
Scientific investigation reports can be trusted because science is based on relationships between causes and effects in nature—an experiment performed under the same conditions will always yield the same results. This is the basic assumption on which all scientific investigations and scientific knowledge are built.
Verification of results by other scientists is the core of science. When scientists report their findings to the scientific community, other scientists attempt the same experiment to verify the results. Depending upon the outcome, the process of peer review may solidify or raise doubts about the results of the original experiment. The results of two similar investigations should be the same and show the same conclusions. When that does not happen, additional trials are attempted to find the error. Scientific knowledge accumulates by the continual review of experiments to verify data and conclusions.
The reliability of scientific results is based on researchers following a code of ethical behavior. Elements of this code include:
Accurately recording and reporting results is critical so that an experiment can be repeated in exactly the same way by anyone. Scientific research depends on careful documentation so independent researchers can reproduce the experiment. When results are not reproducible, they cannot be accepted by the scientific community.
This happened in 1989 when the results of a now-famous “cold fusion” experiment were announced. The potential new source of energy received wide coverage in the press; however, when other scientists attempted to reproduce the results from the experiment, they obtained entirely different results. What happened?
No one is sure exactly why the cold fusion results were not reproducible. There may have been a problem with the experimental design that was overlooked. Perhaps a second independent variable was introduced or some condition was not controlled, so that the exact procedure could not be determined. Whatever the cause of the error, the results have not been accepted as valid because they are not reproducible. Needless to say, this did nothing positive for the professional integrity of the scientists involved.
It is important that all results be reported. Sometimes an experiment produces data that are not expected or appear to be inconsistent with earlier data. These inconsistencies must be recorded and analyzed just like all the rest of the data.
Unexpected data may lead to new questions and research directions. Therefore, it is important to accurately record the exact methods and equipment used and all data obtained in an experiment. Scientists generally report their results at conferences or in scientific journals that are reviewed by other scientists. One of the problems encountered by the cold fusion researchers was that results were released to the general media prior to review by other scientists.
Perhaps the most important ethical consideration in scientific research is to avoid influencing, or biasing, the results of an experiment. Bias occurs when the results are skewed by the expectations of the scientist to a particular outcome. Bias can be as innocuous as accidentally altering an experimental procedure, but also include the blatant changing of recorded data to obtain the expected or desired result. The latter case constitutes fraud and is a very serious breach of scientific ethics. Often times, however, bias is more subtle. If the experimenter expects a particular result, he or she may tend to accept results that support the expectation and reject results that do not, perhaps without any conscious realization of having done so.
The design of many experiments prevents bias by using a “double-blind” technique. Because the results can be influenced by an expectation that an action will work, neither the subjects nor the researchers know which subjects received the control or the variable being tested. A carefully designed experiment searches and accounts for all types of bias before the experiment begins.
A key part of any scientific investigation is the hypothesis—a possible explanation for a phenomenon that can be tested. A hypothesis is sometimes referred to as an educated guess, but it is actually more than that; it is a tentative explanation for something that has been observed. The hypothesis sets the design for the experiment. In other words, the experiment is testing the truth of the hypothesis.
For example, in the early 17th century most people believed that all celestial bodies revolved around Earth. Nicolaus Copernicus carefully observed the motions of the planets and formulated a hypothesis that the sun, not Earth, was the center of the Solar System—a heliocentric system. His hypothesis, or possible explanation, was based on observations. Of course, not everyone was immediately convinced. Other hypotheses or explanations of the motions of stars and planets already existed. More testing of his hypothesis was needed to verify the truth of his hypothesis. So other scientists replicated his experiments and made similar observations and collected data in other locations. One observation that supported the heliocentric hypothesis was that the planets sometimes appear brighter and sometimes dimmer. The relative positions of the sun, the planets, and the Earth change in different ways in a heliocentric system than in a geocentric system, and the observed patterns of brightness also corresponded to a heliocentric system. The fundamental change from a geocentric universe to a heliocentric solar system was a paradigm shift that brought a scientific revolution.
A hypothesis is useful for a scientific investigation if it has certain features. First, it must make a prediction that can be tested. How does Copernicus’s heliocentric universe stack up to this requirement? He could predict the positions of the planets far into the future (that could be falsified) and later observations supported the hypothesis. Second, the hypothesis must be falsifiable. If the hypothesis is not correct, there are tests or experiments that will show it to be incorrect. If the motion of the celestial bodies is not consistent with the hypothesis, it can be shown to be incorrect. In fact, parts of the Copernican hypothesis (that planets move in uniform circular motions around the sun) were later falsified. The observed motions of the planets are not consistent with these circular orbits; planets actually move in elliptical orbits around the sun. The Copernican hypothesis, although not completely correct, eventually led to an understanding of the solar system that allowed people to walk on the moon and robots to explore Mars.
Science is based on testable hypotheses, using the scientific method described below. Pseudoscientific fields, such as astrology, fortune telling, therapeutic touch, and studies of UFOs are generally built on a foundation based on beliefs and encompass hypotheses that are not falsifiable. When the data support the “hypothesis,” they are presented as proof. When they do not, there is always an explanation, which cannot be tested. This is not science and there is no confusion about what is and what is not scientific.
Which of the following could be a scientific hypothesis?
The correct answer is C. Choice C makes a prediction that can be tested. It can also be falsified if cats demonstrate to have hearing that is as good as, or better than, that of dogs. Choice D is not falsifiable because there is no way to prove that people do not know what their pets are thinking. Choices A and B do not make testable predictions.
Forming a hypothesis is only one step of the scientific method.
The hypothesis is a tentative explanation, but it is not really useful until there are data to support it. Using a prediction based on your hypothesis, you can design an experiment to test the prediction. An experiment is a set of controlled tests and observations of the results that determine whether the prediction is correct. Although an experiment can show that you were unable to disprove the hypothesis, you can never truly verify hypotheses beyond further testability. In other words, the best you can do in scientific inquiry is to not refute a hypothesis. Skepticism always remains and empowers science to achieve hypotheses that can later become theories, and perhaps even laws.
The experiment must be designed to actually test the hypothesis, providing an answer that will support it or disprove it. For example, how can you design an experiment to test a hypothesis that small mammals are likely to eat sunflower seeds and thistle seeds equally? If you place only thistle seeds in a feeder and count the number of small mammals that eat them, your data does not test the hypothesis. What if no small mammals show up? That could either mean that the small mammals do not like thistle seeds or that there are no small mammals in the area. In addition, it provides no data about whether they eat sunflower seeds. However, if you place two identical feeders side by side, one holding sunflower seeds and the other holding thistle seeds, and there are small mammals in the area, your experiment can test the hypothesis. If the small mammals spend equal time at the two feeders, the hypothesis is supported. Keep in mind that a single test does not prove the hypothesis to be true. If no small mammals arrive at either feeder, you still do not have useful data, because there are several possible explanations for the observation that do not have anything to do with your hypothesis. On the other hand, if all the small mammals go wild over the sunflower seeds and ignore the thistle seeds altogether, the hypothesis is not supported by the observations.
Which observation supports the hypothesis that fire ants produce a substance that is harmful to humans?
Answer C is the correct answer because the statement predicts some kind of adverse reaction. Choices A and B are observations that are unrelated to toxicity. There are nontoxic, red insects. Although people may be afraid of fire ants because they inflict pain, the fear itself is not evidence of toxicity. In fact, many people are afraid of insects that do not produce toxins.
An experiment must produce unambiguous results. You can accomplish this by designing the test so that only one variable is changed at a time. Let’s go back to the small mammals and the seeds. The previous paragraph refers to placing different types of seed in two identical feeders. Why is the word “identical” italicized? There must be some reason for the emphasis. Well, what if you placed the sunflower seeds in a platform feeder and the thistle seeds in a tube feeder? Now you observe the small mammals eating sunflower seeds, but you still do not have support for the hypothesis. Why? It is possible that the small mammals do not prefer one seed over the other, but instead, prefer one type of feeder over the other. The experiment does not test the hypothesis because two variables were changed. One change—the type of seed—tests the hypothesis. The other change—the type of feeder—does not. You do not know whether your experimental results are due to one change or the other or both.
The table below shows some examples in which an independent variable— the factor that is being tested and is manipulated by the experimenter as part of the test—affects the dependent variable—a measurable event that changes in response to changes of the independent variable.
| Variables | |
|---|---|
| heating time (minutes) | temperature (°C) |
| 0 | 45 |
| 1 | 68 |
| 2 | 88 |
| 3 | 100 |
| 4 | 100 |
| 5 | 100 |
In well-designed experiments, all factors, except the independent variable, should be identical in each test. For example, to test the prediction that plants grow bigger if they have more light, a researcher might expose several plants to different amounts of light (independent variable) and measure growth (dependent variable). Other parameters, such as temperature, water, and fertilizer, must be the same for each plant in order to ensure that the change in the growth rate is a result of the difference in the amount of light. These factors are the controlled variables or constants. In the bird feeding experiment, identical feeders were chosen—a controlled variable.
Which of the sets of variables could be used in an experiment to test the hypothesis that different metals absorb different amounts of energy from sunlight?
The correct answer is C. If you want to determine the effect on different types of metals, your independent variable (the one you change) is the type of metal. The effect on the dependent variable tests your hypothesis. The temperature of the metal is related to energy absorption. Other variables, such as type and amount of lighting, and the size of the metal pieces, must be controlled.
After data are collected, the results of the test are analyzed to reach a conclusion. The conclusion may indicate that the experiment supports the hypothesis because the prediction is unable to be refuted by the data. Keep in mind that this does not prove the hypothesis—it only shows that the hypothesis is not untrue. An interesting thing about experiments is that the results may not match the original prediction. This is not necessarily a bad thing. The data are still useful. The scientific method is a cycle, not a linear progression. When the data do not match the hypothesis, scientists may challenge the original findings or modify their hypothesis and design a new experiment. What do you do if all of the small mammals flock to the sunflower seeds? It’s time for a new hypothesis: small mammals prefer sunflower seeds to thistle seeds.
A well-designed investigation not only tests the hypothesis, but also leads to new questions and further investigations. While observing the small mammals, you may have noticed that the thistle feeder attracts birds. Why does one type of bird prefer one food and another prefer a different food? There may be a new hypothesis and series of experiments just waiting for the right scientist.
How does the scientific method work?
The correct answer is D. The scientific method is based on the testing of falsifiable hypotheses that are based on observations. If these hypotheses are shown to be untrue, new hypotheses are developed and tested. When hypotheses are unable to be refuted, they are tested in new experiments. Although we commonly assume some very well-known hypotheses, they can never strictly be proven.
A single test does not prove a hypothesis, but it can support it. Generally a hypothesis must be tested by many different scientists working in different laboratories before it is generally accepted. A theory is an explanation of the natural world that incorporates verified and replicated data and the accompanying conclusions based on a well-tested hypothesis. Theories are not static knowledge. As new experiments and observations expand the base of knowledge, they are incorporated into the theory. For example, chemists have refined the atomic theory to account for observations about how atoms interact. In the early 20th century, a model was developed, showing electrons moving in fixed orbits around the nucleus, which could explain what was known about how atoms behaved. This model was incorporated into the atomic theory. Later experiments were not consistent with that model and the theory was modified. According to the current atomic theory, the model represents electrons by a “cloud” of likely electron locations. As new discoveries are confirmed, new observations may challenge this model. As experimental discoveries change our understanding of the truth, the theory may have to be modified again. This is how science works—truth builds upon truth.
In common use, the words theory and hypothesis are often used interchangeably; in science they represent very different concepts. This difference in usage has sometimes led to the misconception that a theory is a guess or belief. In science, a theory is supported by a large body of evidence based on many hypotheses and it is a tool for predicting experimental results and understanding how the natural world works. While a theory can serve as an explanation of observed phenomena, it also serves as a starting point for new investigations into predicted phenomena. Some theories have generated many new hypotheses, expanding the reach of an entire field of science.
There are thousands of theories in science, ranging from explanations of one particular phenomenon to theories that encompass entire fields of scientific understanding. Some of the most influential theories that have driven scientific research over the past few centuries are discussed on the next couple of pages.
Although the concept of atoms was first introduced by ancient Greek philosophers, it was not a scientific theory because it was not supported by experimental data. In the early 1800s, John Dalton designed experiments to test the existence of atoms as the basic units of the elements. Dalton modeled the atom as a hard ball—the basic particle of matter. Building on his work, later researchers have developed new models. According to modern atomic theory, the atom is composed of smaller charged and uncharged particles, held together by forces of attraction. Dalton’s basic idea—that an atom is the smallest particle of an element—is still a key part of atomic theory. The atomic theory is the basis of all of our applications of chemistry, including all sorts of modern materials and pharmaceuticals.
One of the implications of Albert Einstein’s theory of relativity is that the universe is expanding. This concept, combined with observations that distant galaxies are moving apart at increasing speeds forms the basis of the Big Bang Theory. According to this theory, the universe began about 14 billion years ago in a sudden expansion from an extremely hot, dense phase. In the 1960s, scientists discovered the Cosmic Microwave Background (CMB)—light waves that permeate the universe. The CMB was one of the predictions of the Big Bang Theory. Today, almost all cosmologists accept the Big Bang as the best theory of the beginning of the universe. Data from the Hubble Telescope and many other space and ground-based observatories support this explanation. The theory has been used to develop an understanding, not only of the broad universe, but also the basic particles that make up all matter.
Classical and quantum mechanics are concerned with the motions and forces that cause the movement of objects. Classical mechanics was first developed over 300 years ago through the work of Newton, Kepler, and Galileo (among others), whereas quantum mechanics is much more recent. The main scientists responsible for our progress in quantum mechanics are Bohr, Planck, and Einstein. The basis of classical mechanics on mathematical explanation was a decisive stage in the development and history of science. Not simply using math in rigorous ways, classical mechanic’s scientists also relied on experimentation for the first time and established the formulation of quantitative predictions, and how to test them by carefully designed experiments and measurements. The main tenets of classical mechanics deal with objects on a human scale and hold for 99.99% of our everyday activities. However, the revelation of quantum mechanics was a major breakthrough for our understanding of all motion—even at the subatomic scale. Quantum mechanics holds for energy, inertia, and the motion of all objects, including waves, and is most notable for the idea that light is a wave-particle duality. In a sense, quantum mechanics is more fundamental than classical mechanics because it provides precise explanations and predictions across all scales. Whereas there are some major holes in classical mechanics, quantum mechanics has yet to be refuted after more than a century of experimentation.
The theory of evolution began with the introduction of natural selection in a joint 1858 paper by Charles Darwin and Alfred Russel Wallace. They both independently, and later together, assembled and collated data from their observations of plants, animals, and fossils to build the theory of evolution by natural selection. Darwin and Wallace hypothesized that evolution occurs when a trait that increases an individual’s chance of successful mating becomes more common from one generation to the next. Evolution affects population genetics and eventually leads to the emergence of new species because individual organisms acquire and pass on novel traits via inheritance. The key element of the theory is that differential survival and reproduction (based on competition for resources and/or mates) allows some organisms to pass on genetic variation to their progeny. Although the theory has been modified since Wallace and Darwin’s time, natural selection remains a key concept on which our current understanding of biology, genetics, and ecology are built. The Modern Synthesis of the early 20th century has incorporated the idea of a gene as the unit of inheritance and we now understand the molecular biology of DNA replication, population and community ecology, and genetics in much greater detail. The theory of evolution is the most powerful theory in the life sciences.
In the early 20th century, Alfred Wegener noted how South America and Africa seem to fit together. He also researched the similarity of fossils at the edges of widely separated continents. He proposed a hypothesis of continental drift, which stated that all the continents had once formed a single land mass that he called Pangaea, but had split and were moving away from one another. Wegener’s ideas were not widely accepted because he lacked an adequate explanation for the mechanism of continental drift. In the 1960s, scientists discovered evidence that supported Wegener’s hypothesis. Magnetic materials in the rocks of the sea floor in the deep ocean provided evidence that the crust of Earth is made of plates that move relative to one another. This observation, as well as the results of other experiments, was combined with Wegener’s continental drift in the theory of plate tectonics. Scientists have used this theory to study the prehistoric structure of the continents and to develop other theories about the internal structure and the history of the planet.
A scientific law is a statement of fact that explains a relationship in nature that is generally accepted to be true and universal. Scientific laws are based on numerous observations and tests, have withstood the test of time with no exceptions being found. Like mathematical postulates, scientific laws do not require proofs. They are accepted based upon a long history of rigorous experimentation, verification, and replication by numerous scientists working independently to prove the law to be untrue. Scientific laws include the law of gravity, conservation of mass, and the gas laws that describe the behavior of gases. In many cases, scientific laws can be expressed as mathematical formulas.
Which of the following is an established scientific theory?
The correct answer is A—plate tectonics is a theory built on a number of tested hypotheses. Intelligent design is not a scientific theory because it is not falsifiable and therefore cannot be tested. Conservation of mass is a scientific law and the internal combustion engine is an example of technology.