Friday, December 3, 2010

Theory vs. Law (12/23/2008)

This was originally posted on a horrible site called Myspace. When Myspace underwent a redesign in Fall 2010, hundreds of insightful reader comments that had been left over the years were lost. I have since deleted my account there.

In the evolution "debate" you frequently hear people discussing the definition of the word "theory" (as in the theory of evolution, germ theory of disease, etc.). That has been written about extensively, so I won't go into it here. But occasionally you also hear a creationist say, "If evolution is so true, why is it still a theory and not a law, like gravity?"

Here's the scoop: In science, a "law" is something that can be described by a simple mathematical equation, one that is never seen being deviated from in nature. So, yes, gravity is a law, because there's a simple equation that predicts how two bodies will react gravitationally to each other, given a couple of variables: their masses and their distances. And it always works out. Force equals mass times acceleration -- that's a law. Energy equals mass times the square of the speed of light is also a law. They're laws because you can test them by plugging in the numbers and comparing the real result to the predicted result, which are always the same.

Natural processes like evolution don't work like that. There's no equation to describe how evolution works, any more than there's an equation that describes how cells divide or how memory is stored in the brain. Biological systems -- unlike, say, the planets and the sun -- are complex and chaotic, with tens or hundreds of variables. You can predict exactly when a solar eclipse will occur because the bodies of the solar system are simple and obey Kepler's and Newton's laws of motion. But you cannot predict the weather three days from now with any certainty, because there is no "law of weather." There are too many variables; each particle of air is doing its own thing.

However, in meteorology we have non-law theories which are very useful and predictive. A cold front moving into warm, moist air will cause precipitation and maybe thunderstorms; that is the prediction from meteorological theory, and from observation we know it is very much a truth. The germ theory of disease predicts that if people inhale anthrax spores, they will contract anthrax. And we know that they will -- we know because the germ theory has been supported to the point of virtual certainty. Even if there isn't a simple equation expressing this knowledge.

"Why isn't evolution a law?" is just another fallacy that creationists and IDers throw up because it sounds half-reasonable, and because they don't know better. Don't let it flummox you.


  1. I agree with you essentially, but that's not quite it either. If you go into just about any physics forum and ask if gravity is a law or a theory, you will get a lot of discussion on it. There is the theory of gravity and gravitation, just as there is the theory of evolution. You see Ed it's not about law vs theory, but rather how the phrasing is worded and used. Gravity is a proven natural phenomenon, as is evolution. It's not a question as to whether they exist or not, but rather the mechanisms by which they work. It's all about the wording.

    Whenever you see the phrase, "Theory of..." it is meant to be the Theory that explains how an established natural phenomenon (law) works. By contrast, whenever you see the same word, but phrased as, "Big Bang Theory", it's meant to both pose the idea and explanation of a possible, yet unproven event, in other words, it really is "just a ttheory". Notice that it is worded "big bang theory" and not "theory of the big bang". Notice how it's referred to as "inflation theory" and not the "theory of inflation", or how it's referred to as "M theory" as opposed to "theory of Membranes". It's all about the phrasing.

    Notice that it is the "theory of gravity", which means it's a law. Now notice how it's always phrased "theory of evolution", never ever "evolution theory". We're not questioning whether gravity or evolution happened or if they even exist or not, we are questioning how these established phenomenas (natural laws) work.

    Long story short, the phrasing "theory of..." questions how a proven law works, not whether it exists or not because we already know it does. The phrasing, "... theory." is meant to question the possible existence of a hypothesized event or state. This is why the phrasing is so important; "theory of..." and "...theory" are not equal.

  2. The law of universal gravitation is a law -- it's an equation describing and predicting the behavior of objects, and objects' behavior is never seen to deviate from this law (at least in non-relativistic, non-galactic contexts).

    General relativity, MOND, loop quantum gravity etc. are theories. They are attempts to explain the foundational underpinnings of the invariant laws that constrain the behavior of objects. It is a subtle distinction.

    I don't know about your syntactical point...sounds like another personal opinion. When I Google "evolution theory" or "quantum theory," there are thousands of legitimate results.

  3. You didn't just... um, okay.

    The wording isn't just a random coincidence and google results aren't evidence. The same can be said of Unicorn Meat and Pixie Dust when they're googled.

  4. Mmmm, unicorn meat with pixie dust...

    It's all just semantics. When you are talking about science, theories and laws imply the same thing. It's just tradition which is used for which one.

    The usual problem is that "theory" is used casually to mean "hypothesis" or even just "idea". That's why the ignorant masses sometimes say that evolution is "just a theory"; they don't know what being a scientific theory implies, which is that it is a law.

    It's the same with "evidence" and "proof", and what they imply in science and math vs. how they are used in common conversation. That often causes annoying confusion by those who don't understand.

    That's my story, and I'm sticking to it.


  5. I don't agree that it's only a matter of semantics. Laws are theories that predict specifically what will always happen given a set of initial conditions. A bunch of laws are embedded in the much broader theories of general relativity and quantum mechanics, but those theories are not themselves laws. They are systems of laws, and to make specific predictions you need to access the appropriate laws within the theory. Same thing applies with evolution, which embeds many laws, such as those that govern DNA replication, in a much broader and more complex theory.

  6. It's oddly hard to find something authoritative on this to reference, but actually that makes sense when you put it that way. "Law of Gravity" vs. "Theory of Gravity" both seem OK, but "Law of Evolution" sounds wrong.

    In any case, the meaning of "theory" is usually only confused when somebody thinks "only a theory" makes something not a fact, and this is only used in the case of the theory of evolution. Nobody says the germ theory of disease is "just a theory", and proceeds to throw their antibiotics in the trash.


  7. The word Theory in science has a specific definition; it means the best current possible explanation for a serious of facts that we have at this moment.

    Because science, unlike religion, is nor dogmatic. Because science, unlike religion, is conditional, science is always open to the possibility that a new fact or experiment will contradict the current scientific theory.

    Religious creationists/intelligent designers love to use this aspect of science to prove their agenda but, of course, it proves nothing.