Hypothesis, Model, Theory and Law

Among the most extremist -and extremely ignorant- of the anti-science crowd you will come across statements such as this: "But evolution is only a theory." Indeed, but scratch the only. In science, the terms Hypothesis, Model, Theory and Law are indeed gradations in a scale but they certainly do not share their coloquial meaning or hierharchy. If you think a scientific theory ever becomes a law or a fact you may need to read the following. Let's go back to the basics.

A Hypothesis is pretty much what people think it is: an educated guess, the suggestion of a Model which needs further testing. And what is a Model exactly? That is a useful but untrue representation of a partially workable Hypothesis. A great example of this is the Bohr model of the atom, which depicts electrons circling the nucleus in an orbit not unlike the solar system: the model is very helpful but it is in no way supposed to be a true depiction of the atom.

Then there is that word. That wretched word so misused and mishandled by creationists that they should be prosecuted for raping the concept. It is of course the term Theory. It is usually synonimous with Hypothesis -but that is not its actual usage in science. Simply put, a Theory is a Hypothesis that has been proven to work, a demonstrated model that explains certain facts. The Theoy of Evolution is not a blind stab in the dark. The Big Bang Theory is not a wild guess.

What is a Law then? How is any Theory worth studying when we have actual natural laws that work as if they were written in stone by a control freak space daddy? As much as it might disappoint those who follow the commandments of sand people that lived two or three thousand years ago, the truth is that a Law is just the fundamental mathematical description of a fact or group of facts that repeat without any known exceptions. Nothing more, nothing less.

For example, the Law of Gravitation basically says "things fall". To be fair, it is a bit more complicated than that: "every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.". That is a Law (and one of the four fundamental forces of the universe) because there has not been observed any exceptions to the rule.

A Law is just a statement of fact. But how did that happen? To answer that we need a Theory, which in the case of the Law of Gravitation is the Theory of Gravity. This goes beyond the simplest mathematical description of the thing and tells us how it actually works and what causes it. Laws are not above Theories -one is only concerned with statements of facts and the other one explains those facts. Both are needed to understand any given phenomenon.

But if that is true how is it that there is not an equivalent supporting Law for the Theory of Evolution? Plainly, evolution cannot be described as a Law because the concept does not apply: there is not, and never will be, a mathematical formulation of evolution. Biology can rarely be expressed with mathematical precision because life is just so complex. Of course, it is technically not impossible to devise a Law of Evolution, but nothing short of omniscience would grant us such a gift of knowledge. Unless we boil it down to "Life evolves," of course.

After making those distinctions it might suddenly become more obvious why it is such an affront to human intelligence to put warnings such as "Evolution is only a theory" in the Biology textbooks of so many American and Islamic children. It might be true that there are hundreds of long, boring books devoted to the tiniest minutia around the philosophical underpinnings of these concepts. But it is also true that these terms can be explained in literally five minutes.

There is no excuse for using the "Only a Theory" argument: these people are either profoundly stupid or maliciously dishonest. None of those tributes qualify anyone to legislate on education.

(El artículo traducido al castellano aquí: Hipótesis, Modelo, Teoría y Ley)