There are some common misconceptions about what "proof" and "theory" mean. I hope to clear up a few of those in this article.

First, the idea that "you can't prove a negative." Ummm ... yeah .... not only can you prove a negative but it's what science is based upon.

Let's take a simple example. In science, you come up with an hypothesis. Let's say that your hypothesis is that mixing salt and water will produce an explosion of catastrophic proportions. So other scientists who disagree with your hypothesis (in addition to culinary experts around the world) set out to prove you wrong.

Now obviously this hypothesis will be disproved. Scientists in their laboratories and my aunt in her kitchen will give the lie to that statement. But what are they proving? That mixing salt and water will NOT produce an explosion of catastrophic proportions. They are proving a negative.

So where did this whole idea come from (the idea that you can't prove a negative)?

It's the universal negative that cannot be proven. I cannot prove that never, ever will mixing salt and water produce an explosion of catastrophic proportions. Who knows? The laws of the universe might alter tomorrow such that mixing those two things would cause untold damage. That, however, is not science; that is speculation. Science deals with what we have here and now, not what we might have there and then.

Now, for an atheist, this has some other ramifications. As an atheist, I claim that there is no god.

I'm claiming also, though not stating it explicitly, that there was never a god and that there never will be a god. My main quarrel with the entire issue is one of definitions.

You and I both know what "salt" is. We agree on what "water" is. We have a shared conception of what "mixing" and "explosion" mean. Though I suspect many might disagree, we probably do not have a shared conception of what the word "god" means.

Definitions matter. In science, they matter more than anywhere else. What does the word "god" mean? Is it a bearded guy sitting on a cloud? Is it a nebulous energy that permeates all things? Is it three hypostases in one godhead, and if so how do you define those terms?

Not only does definition matter but there is this whole "testability" thing. This goes back to what what I was talking about right at the start: proving a negative. If I cannot disprove what you are saying then it is not a scientific statement.

Let me clarify that. I am not saying that my inability to come up with a disproof of your statement affects its validity; not at all. However, if your statement is phrased such that there is no possible disproof, then it is not science. Science not only welcomes criticism and disproof, it will often explain how exactly to go about doing that very thing. Science is not difficult, but it is rigorous.

This bring us to the next concept ... Theories.

Everybody has theories. Some theorize that JFK was killed by order of Congress. Some theorize that apes evolved into humans. Some theorize that the moon is made of green cheese. None of those is actually a theory, scientifically speaking, and at least two are completely false.

Let's start by saying what a theory is not. A theory is not a "guess." It is not even a "best guess." A theory, in scientific terminology, means our best explanation of how the facts fit together. A theory does not claim to be absolute truth in the same way that the Koran or the Bible claims to be absolute truth. Science wants to be proven wrong, although some scientists may not.

A theory is not a waypoint on the journey to becoming a law. There is no "now you're the theory of caramelization" and "now you're the law of caramelization" It does not work that way.

There can be laws and theories about the same thing. There is a law of gravity. If you drop something, it will fall downwards. (Assuming you are on the Earth or an equivalent territory.) There are also a few theories of gravity. The laws explain WHAT happens while the theories attempt to explain WHY it happens.

In the same sense, there are theories of evolution. These theories attempt to explain why the offspring of a brown­eyed male and a green­eyed female has blue eyes. (OK, that's more genetics than evolution, actually, but the connection is clear.) There is also the FACT of evolution which those without a PhD which involved more than six months of "classes" might dispute.

There are theories of evolution. Evolution is a fact. There are theories of gravity Gravity is a fact. I welcome those who disagree to step off of a thirty­story building and prove me wrong.