Theory
From SkepticWiki
Contents |
[edit] Definition
A theory, in science, is a well-tested set of laws and facts which explains and predicts some collection of facts.
[edit] Quotations
- Theory: In science, a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses. --- US National Academy of Sciences [1]
- "Theory" means a logical, tested, well-supported explanation for a great variety of facts. --- National Center for Science Education, USA [2]
- Theory: A scientifically testable general principle or body of principles offered to explain observed phenomena. In scientific usage, a theory is distinct from a hypothesis (or conjecture) that is proposed to explain previously observed phenomena. For a hypothesis to rise to the level of theory, it must predict the existence of new phenomena that are subsequently observed. A theory can be overturned if new phenomena are observed that directly contradict the theory. --- NASA[3]
- Scientific theories, like evolution and relativity and plate tectonics, are hypotheses that have survived extensive testing and repeated verification. Scientific theories are therefore the best-substantiated statements that scientists can make to explain the organization and operation of the natural world. Thus, a scientific theory is not equal to a belief, a hunch, or an untested hypothesis. --- American Geophysical Union [4]
- A theory in science, such as the atomic theory in chemistry and the Newtonian and relativity theories in physics, is not a speculative hypothesis, but a coherent body of explanatory statements supported by evidence. --- American Intitute of Biological Science [5]
[edit] Theories and facts
There is a popular misconception that a theory is a weaker term than fact: that a theory is a putative fact not yet adequately proven. This misconception is fostered partly by the popular usage of theory to mean "guess, hypothesis, hunch", and partly by the incessant work of creationists who wish to delude the public into thinking that the use of the phrase "theory of evolution" implies that scientists do not have complete confidence in, or adequate proof of, that theory.
But, as we have seen, the word "theory" carries no such connotations in scientific usage. A theory is a well-tested explanation for a body of facts.
For this reason, "fact" and "theory" are relative terms. For example, the idea that the world is round may be considered a theory from the point of view of cartography: to a cosmologist, it is a fact to be explained by a theory of solar system formation. In the same way the idea that evolution has happened might be regarded as a theory by paleontologists, who can use this to explain the facts of the fossil record. But it is regarded as a fact by biologists, who then propose the theory of evolution to explain the fact of evolution.
It might indeed be said that everything we call a fact is also a theory, with the exception of such facts as: "I am currently having such and such a sensory experience"; "I have such-and-such a memory"; or "I am experiencing such-and-such an emotion". Every other fact, such as "There is a tiger over there" is a theory which accounts, in the case of this example, for the sensations of seeing black and orange stripes and hearing growling. Or "There was a clown at my tenth birthday party" might be regarded as a theory to account for the fact that you have memories of a clown being at your tenth birthday party.
[edit] Theories and laws
There is also a misconception that a theory, once sufficiently proven, becomes elevated into a law: that a theory is a putative law not yet adequately proven. But, as we have seen, a theory consists of a collection of laws and facts.
One might indeed say that a theory is a collection of laws sufficiently large to make interesting predictions. Consider Newton's law of gravity: F = Gm1m2/r2. This tells us what force will exist between two masses at a given distance. But this has no predictive power whatsoever unless we also have laws of motion telling us what happens to an object when a force acts on it: together with the law of gravity, these laws make up the Newtonian theory of gravity, which makes testable predictions.
To take another example, the Second Law of Thermodynamics, in the Clausius statement of that law, can be given as: "There's no such thing as a refrigerator without a power source". This has a little predictive power, but only about refrigerators. However, when we combine it with the First Law of Thermodynamics, we have a theory from which many much more interesting consequences can be derived.
[edit] Theories and hypotheses
A hypothesis is a weaker term than theory: it means a theory or fact that has not been sufficiently tested and proved. To put it another way, a theory is a hypothesis which has stood up to extensive testing and is supported by the data.
Some writers on science, especially popular science writers, will however use the term "theory" to denote any hypothesis, not matter how unsubstantiated. Conversely, as we have remarked, creationists often try to pretend that the word "theory" actually means "hypothesis".
A further confusion is that sometimes well-established theories will, for historical reasons, be referred to as hypotheses. A prominent example is the "Wobble Hypothesis", which we shall sketch out very briefly: the genetic code exhibits redundancy: for examples, the ribosomes of a cell will translate the both the codons AGU and AGC as the amino acid serine. The Wobble Hypothesis proposes that instead of there being one mechanism to translate AGU as serine and another mechanism to translate AGC as serine, there is a single mechanism for translating codons into serine which can't tell the difference between the codons AGU and AGC: and the same with other redundancies in the genetic code. When this was first proposed, it was a hypothesis: it has now been proved so definitively that no-one doubts it, but it is still referred to by the name that it was first given --- the "Wobble Hypothesis".
We should also note the use of the term "Conspiracy Theory". This is invariably used to describe a hypothesis that has not been proved; in fact, many such "theories" are so vague and unfalsifiable that they do not even deserve the name "hypothesis". This is confusing, but the term is in such common useage that there's nothing to be done about it.
