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Questions and Answers about Scientific Theories


1. If scientific theories are the most important ideas in science, and scientists are confident in their validity, why are they still referred to as just theories?

Scientific theories are arrived at through inductive reasoning rather than deductive reasoning so that within the strict framework of logic these ideas must be referred to as theories. This would seem simple enough, yet there is confusion about the meaning of this word since most of the public and even astrophysicists often use the word theory when they should be using the word hypothesis.

2. What determines if a scientific idea / model is a hypothesis or a theory?

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The analogy of solving a board puzzle is helpful in clarifying the distinction between theory and hypothesis. There may be several puzzle pieces that could be possible candidates to fill an open space in the puzzle. These puzzle pieces would be considered possible hypotheses. On trying out each of the puzzle pieces one of the pieces may appear to fit one of the sides of the puzzle. At this point it may be tempting to upgrade the status of that puzzle piece from being a good hypothesis to being a theory, but actually that puzzle piece is still only a hypothesis. Caution is needed because as more evidence comes in, or in the case of the board puzzle as more pieces fit around it, occasionally a piece that we thought fit on one side will not match up on another side and so our hypothesis must be rejected. It is only when our piece proves itself by fitting on at least two or three sides that we can be confident that our piece fits the puzzle. In the same way, only when there are multiple distinct logical arguments based on factual evidence can we upgrade our hypothesis to the status of being called a theory.

Finally, again similar to our board puzzle piece, when the correct theory fits into our base of knowledge it does much more than just seem to fit with the surrounding evidence. Whereas a hypothesis just seems to fit some of the facts, a theory allows us to see the big picture so as to make sense of all of the evidence that surrounds it. Theories are the most important ideas in science because they allow us to see the significance of what was before just random information.

3. What is wrong with the Sherlock Holmes type deductive reasoning statement: If all of the possible hypotheses are eliminated except for one, then that hypothesis, no matter how unlikely, is the correct hypothesis?

Because deductive reasoning draws conclusions with complete certainty, it is tempting to sometimes believe that we are using deductive reasoning when in fact we are using inductive reasoning. The fictional Sherlock Holmes makes this mistake. Rarely if ever, can our reasoning concerning nature be considered to be deductive reasoning. The problem with doing so is that this implies that all of the possible hypothesis can be identified, when in fact we may never know all of nature’s secrets. This is why it is so important to conduct experiments and collect field data to verify our logic. Through these experiments we often learn of nature’s secrets that are then added to our base of knowledge.

Even though inductive reasoning does not draw conclusions with complete certainty, it is generally much more helpful than deductive reasoning. Inductive reasoning allows us to reach conclusions on what has not been directly observed based on what has been observed. It is inductive reasoning that allows geologists to use present observations to draw conclusions about events that happened million of years ago in the Earth’s distant past. More often it is inductive reasoning that allows us to use observation of the past to anticipate probable events of the future. For example, if every day a bus stops by a bench at 4:00 pm, and we are sitting on that bench a few minutes before four, we would be expecting a bus to arrive within a few minutes. Notice that while our inductive reasoning may be correct the vast majority of times it is still not guaranteed to always be true. No matter how consistent the bus may be, we can not say with complete certainty that the bus will be there each day at the predicted time.

When attempting to solve a problem we would like to consider all of the reasonable hypotheses. But to believe that we can identify all of the possibilities is often the equivalent to stating that we have limited imagination.

4. Scientific theories are arrived at through inductive reasoning, so is it not true that that they can never be proven?

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Well, yes and no. In following the strict rules of logic one could claim that no matter how many arguments appear to confirm the theory there is technically still the possibility of it being wrong. However in realistic terms, when several sound arguments lead to agreement on the same conceptual model, the odds against the theory being wrong become so extremely small that for all practical purposes there can be no other answer. Referring again to the board puzzle example, let us say that a piece has appeared to fit on one side, but then it is matched on a second side, and then three and then finally all four sides fit the puzzle. Once the puzzle piece seamlessly fits into a puzzle, isn’t it a bit ridiculous to continue arguing about whether it belongs?

What can and often does happen to a theory is that new evidence will lead to slight, yet important, modifications of the theory. When biologists test the Theory of Evolution, they know that their chances of overturning the Theory of Evolution is effectively nil. But scientists continue to experiment in the hopes that they might gain a deeper understanding of how evolution works. For example, Darwin favored what is now called gradualism evolution by suggesting that the birth of a new species came about through a gradual separation from the original. Yet the recent evidence shows that it is far more common for the new species to evolve from small isolated populations that might later quickly displace the larger populations. Because of this punctuated equilibrium form of evolution, the fossil evidence tends to show more abrupt changes in species than what a gradual separation would suggest. This modification of Darwin’s original idea is certainly not an overthrow of evolution theory, but rather an important improvement in understanding how the process works.

5. What is an example of a scientific theory?

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The Copernican heliocentric model of the solar system is good example of how these guidelines show it to be a scientific theory.

For the purpose of a providing a simpler explanation for the movement of the planets, Nicolaus Copernicus suggested that the Sun rather than the Earth is the center of what was then thought to be the universe. Two of the many strong points of the Copernican model were that it gave a logical explanation for the phases of the Moon and the apparent retrograde motion of Mars as seen from the Earth. Yet like many scientific truths it was unsetting to many people to think that the Earth is not the center of the universe so more evidence was needed before it could be accepted. At this point the Copernican model would be considered a strong hypothesis rather than being a theory.

It was only much later when the philosopher Giordano Bruno promoted its merits throughout Europe and the scientists Galileo Galilei and Johannes Kepler provided the additional evidence that was needed to raise the status of the idea to that of being a theory.

Kepler used the precise data of another astronomer, Tycho Brahe, to discover that all of the planets move in an ellipse with the Sun at a focus. This is a powerful argument that the Sun rather than the Earth is the center.

Galileo’s contributions came from constructing one of the first telescopes and then using this new technology to record observations. With his telescope he observed mountains on the surface of the Moon, additional moons orbiting Jupiter, the phases of Venus, and sunspots on the Sun. He then presented how these observations supported the heliocentric model of the solar system in his publication Dialogue Concerning the Two Chief World Systems.

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Independently, and even collectively, because all of these arguments are based on inductive reasoning, they do not prove that the Sun is the center of the solar system. But when taken collectively, it becomes effectively impossible for all of these arguments to lead to the same conclusion without that being the correct conclusion. Each argument is like the side of the puzzle piece in that each argument might help or disprove a hypothesis just as there can be a fit or a mismatch on any one side of a puzzle piece. But with ever argument that supports the same conclusion it becomes increasingly more ridiculous to argue against that conclusion being correct. The hypothesis passes the test to being classified as a scientific theory when there are several strong independent arguments based on sound evidence all supporting the same conclusion.

6. Is the Theory of Evolution a true scientific theory?

The Theory of Evolution is a true scientific theory because it passes the test of having several independent arguments based on evidence all leading to the same conclusion. Furthermore the Theory of Evolution has demonstrated its ability as a powerful tool for making sense of the evidence that surrounds it. The Theory of Evolution has proven itself to be one of the most important of all scientific theories.

7. If the Theory of Evolution is a true scientific theory, then why is there still controversy?

Almost everyone believes that they are open to new ideas, and yet in reality, many if not most people are unwilling to adjust their fundamental beliefs. Many people see the Theory of Evolution as an affront to their belief that human beings are uniquely gifted apart from the other species of the planet. However there is no scientific evidence supporting the belief that we are endowed with an ancestral lineage separate from that of the other species. This truth upsets many people such that they would rather ignore the overwhelming evidence than to give up their belief.

By closing their minds to the overwhelming evidence, they envision that the Theory of Evolution is only a hypothesis so that there might remain hope that it can be defeated. In attacking evolution, often times by distorting the truth, their intention is not to promote better science but instead to fulfill their wishful agenda. While constructive criticism is welcome by all of us who seek improvement, it is clear that these critics of evolution promote an anti-science philosophy that is damaging to the success of our culture.

Good science seeks the truth about our reality regardless of how it makes us feel. However it is human nature to be self-centered and so we are more willing to listen to those who make us feel important. Even scientists, being human, are sometimes upset by the truths that they discover. But if we are to be successful at interacting with our reality then we need to show maturity in accepting the truth. We are not at the center of the universe, the Earth is not just six thousand years old, and human beings were not uniquely created from that of the other species. As a general rule that is helpful in determining the truth, any argument placing us at the center of attention is most likely deceiving us by playing on our human need to feel important and so it is almost certain to be wrong. But by fighting this human weakness we show maturity and we are then better able to make wise decisions.

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