In ordinary language, such a confusion of terms is inconsequential, but:
Scientific Laws, Hypotheses, and Theories
Lay people often misinterpret the language used by scientists. And for that reason, they sometimes draw the wrong conclusions as to what the scientific terms mean.
Three such terms that are often used interchangeably are "scientific law," "hypothesis," and "theory."
In layman’s terms, if something is said to be “just a theory,” it usually means that it is a mere guess, or is unproved. It might even lack credibility. But in scientific terms, a theory implies that something has been proven and is generally accepted as being true.
Here is what each of these terms means to a scientist:
Scientific Law: This is a statement of fact meant to explain, in concise terms, an action or set of actions. It is generally accepted to be true and univseral, and can sometimes be expressed in terms of a single mathematical equation. Scientific laws are similar to mathematical postulates. They don’t really need any complex external proofs; they are accepted at face value based upon the fact that they have always been observed to be true.
Some scientific laws, or laws of nature, include the law of gravity, the law of thermodynamics, and Hook’s law of elasticity.
Hypothesis: This is an educated guess based upon observation. It is a rational explanation of a single event or phenomenon based upon what is observed, but which has not been proved. Most hypotheses can be supported or refuted by experimentation or continued observation.
Theory: A theory is more like a scientific law than a hypothesis. A theory is an explanation of a set of related observations or events based upon proven hypotheses and verified multiple times by detached groups of researchers. One scientist cannot create a theory; he can only create a hypothesis.
In general, both a scientific theory and a scientific law are accepted to be true by the scientific community as a whole. Both are used to make predictions of events. Both are used to advance technology.
The biggest difference between a law and a theory is that a theory is much more complex and dynamic. A law governs a single action, whereas a theory explains a whole series of related phenomena.
An analogy can be made using a slingshot and an automobile.
A scientific law is like a slingshot. A slingshot has but one moving part--the rubber band. If you put a rock in it and draw it back, the rock will fly out at a predictable speed, depending upon the distance the band is drawn back.
An automobile has many moving parts, all working in unison to perform the chore of transporting someone from one point to another point. An automobile is a complex piece of machinery. Sometimes, improvements are made to one or more component parts. A new set of spark plugs that are composed of a better alloy that can withstand heat better, for example, might replace the existing set. But the function of the automobile as a whole remains unchanged.
A theory is like the automobile. Components of it can be changed or improved upon, without changing the overall truth of the theory as a whole.
Some scientific theories include the theory of evolution, the theory of relativity, and the quantum theory. All of these theories are well documented and proved beyond reasonable doubt. Yet scientists continue to tinker with the component hypotheses of each theory in an attempt to make them more elegant and concise, or to make them more all-encompassing. Theories can be tweaked, but they are seldom, if ever, entirely replaced.
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hypothesis - a proposition explaining the occurrence of a phenomenon or phenomena, often asserted as a conjecture to guide further investigation. After dropping the ball from one height several times, you may think that dropping it from a greater height will lead to a different response, and you may predict that different response. Your prediction is a hypothesis, and you can test it by changing the height of the drop and observing the result. At that point, you'll have done an experiment to test your hypothesis.
multiple working hypotheses - a method of research where one considers not just a single hypothesis but instead multiple hypotheses that might explain the phenomenon under study. Many of these hypotheses will be contradictory, so that some, if not all, will prove to be false. However, the development of multiple hypotheses prior to the research lets one avoid the trap of narrow-mindedly focusing on just one hypothesis.
The Web has more on Multiple Working Hypotheses
theory - a coherent set of propositions that explain a class of phenomena, that are supported by extensive factual evidence, and that may be used for prediction of future observations. For our rather trivial example, a theory would emerge only after a huge number of tests of different kinds of balls at different heights. The theory would try to explain why different kinds of balls bounce differently, and it ought to be useful in predicting how new materials would behave if dropped as balls in the same way.
Scientists have produced lots of familiar theories:
- - - Copernicus's theory of the heliocentric solar system,
- - - Newton's theory of gravity,
- - - Einstein's theory of relativity, and
- - - Darwin's theory of natural selection are a few.
Each of these theories draws on huge numbers of facts:
- - - observations of the passage of the sun and planets for the heliocentric theory;
- - - the behavior of the planets, of projectiles, and rather famously of apples for the theory of gravity, and
- - - the existence and location of fossils, as well as the modern distribution and reproduction of organisms, for the theory of natural selection.
Some people dismiss a given scientific idea with "That's just a theory". They're right - all science can provide is theories. However, those theories have proven quite useful to all of us. Most of us won't step off the top of a building because of the results predicted by Newton's theory of gravitation - and yet it's just a theory. NASA and other space agencies launch space craft to distant planets on the basis on Newton's theory of gravitation and Copernicus's theory of the heliocentric solar system - and yet they're just theories. It's instructive to remember that Copernicus was required by the authorities of his time to preface his work as just a series of "hypotheses", and not even as a "just a theory".
evidence - the physical observations and measurements made to understand a phenomen. Perhaps equally important is what's not evidence: theories aren't evidence, and the opinions of even the most learned scientists aren't evidence.
Note that evidence is one of the critical underpinnings of a theory (see above). A good scientist or observer of science periodically asks, "What do we think we know, and why do we think we know it?" The answer to the second part should be some sort or sorts of evidence, as defined in the previous paragraph.
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