In the debate over whether God exists, we have theists on the one side, atheists on the other, and, in the middle, science. Atheists claim there is scientific proof that God is not real. Theists, on the other hand, insist that science, in fact, has been unable to prove that God does not exist. According to atheists, however, this position depends upon a mistaken understanding of the nature of science and how science operates. Therefore, it is possible to say that, scientifically, God does not exist—just as science discounts the existence of a myriad of other alleged beings.

What Science Can and Cannot Prove

To understand why "God does not exist" is a legitimate scientific statement, it's important to understand what the statement means in the context of science. When scientist say, "God does not exist," they mean something similar to when they say "aether does not exist," "psychic powers do not exist," or "life does on the moon does not exist."

All such statements are shorthand for a more elaborate and technical explanation, which is that this alleged entity (or God) has no place in any scientific equations, plays no role in any scientific explanations, cannot be used to predict any events, does not describe anything or force that has yet been detected, and there are no models of the universe in which its presence is either required, productive, or useful.

What should be most obvious about the more technically accurate statement is that it isn't absolute. It does not deny for all time any possible existence of the entity or force in question; instead, it's a provisional statement denying the existence of any relevance or reality to the entity or force based on what we currently know. Religious theists may be quick to seize upon this and insist that it demonstrates that science cannot "prove" that God does not exist, but that requires far too strict of a standard for what it means to "prove" something scientifically.

Scientific Proof Against God

In "God: The Failed Hypothesis—How Science Shows That God Does Not Exist," Victor J. Stenger offers this scientific argument against the existence of God:

Hypothesize a God who plays an important role in the universe. Assume that God has specific attributes that should provide objective evidence for his existence. Look for such evidence with an open mind. If such evidence is found, conclude that God may exist. If such objective evidence is not found, conclude beyond a reasonable doubt that a God with these properties does not exist.

This is basically how science would disprove the existence of any alleged entity. If God existed, there should be concrete evidence of His existence—not faith, but tangible, measurable, consistent evidence that can be predicted and tested using the scientific method. If we fail to find that evidence, then God cannot exist as defined.

Certainty and Doubt in Science

Of course, nothing in science is proven or disproven beyond a shadow of any possible doubt. In science, everything is provisional. Being provisional is not a weakness or a sign that a conclusion is weak. Being provisional is a smart, pragmatic tactic because we can never be sure what we'll come across when we round the next corner. This lack of absolute certainty is a window through which many religious theists try to slip their god, but that's not a valid move.

In theory, it may be possible that someday we will come across new information that will lead us to further explore the God hypothesis. If the evidence described in the above argument were found, for example, that would justify a rational belief in the existence of the sort of god under consideration. It wouldn’t prove the existence of such a god beyond all doubt, though, because belief would still have to be provisional.

It may also be possible that the same could be true of an infinite number of other hypothetical beings and supernatural forces. Zeus or Odin, Christian or Hindu—every possibility of a God or gods is up for exploration.

What Does it Mean to "Exist"?

Finally, for such a proposition as "God exists" to have meaning to science, we need to define what "existence" in this case means. When it comes to God or a series of gods, their existence is dependent on evidence that they have had or continue to have an impact on the universe. In order to prove impact on the universe, there must be measurable and testable events that could best or only be explained by whatever this "God" is we are hypothesizing. Believers must be able to present a model of the universe in which some god is "either required, productive, or useful."

This is obviously not the case. Many believers work hard trying to find a way to introduce their god into scientific explanations, but none have succeeded. No believer has been able to demonstrate, or even strongly suggest, that there are any events in the universe that require a supernatural being to explain.

Instead, these constantly failing attempts end up reinforcing the impression that there is no "there" there—nothing for "gods" to do, no role for them to play, and no reason to give them a second thought.

So far, everyone who has tried to scientifically prove that God exists has failed. While it's technically true that this doesn't mean that no one ever will succeed, it is also true that in every other situation where such failures are so consistent, we don't acknowledge rational or even serious reasons to bother believing.