A popular objection to atheists' arguments and critiques of theism is to insist that one's preferred god cannot be disproven — indeed, that science itself is unable to prove that God does not exist. This position depends upon a mistaken understanding of the nature of science and how science operates. In a very real and important sense, it is possible to say that, scientifically, God does not exist — just as science is able to discount the existence of a myriad of other alleged beings.
What Can Science Prove or Disprove?
To understand why "God does not exist" can be a legitimate scientific statement, it's important to understand what the statement means in the context of science. When a scientist says "God does not exist," they mean something similar to when they say "aether does not exist," "psychic powers do not exist," or "life does not exist on the moon."
All such statements are casual short-hand for a more elaborate and technical statement: "this alleged entity has no place in any scientific equations, plays no role in any scientific explanations, cannot be used to predict any events, does not describe any thing 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 and is modified form of the argument from a lack-of-evidence: God, as defined, should produce evidence of some sort; if we fail to find that evidence, God cannot exist as defined. The modification limits the sort of evidence to that which can be predicted and tested via the scientific method.
Certainty & Doubt in Science
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 requiring or benefiting from some sort of "god" hypothesis in order to better make sense of the way things are. 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.
By the same token, though, it may be possible that the same could be true of an infinite number of other hypothetical beings, forces, or other things which we might invent. The mere possibility of existing is one that applies to any and every possible god, but religious theists only try to use it for whatever god they happen to personally favor. The possibility for needing a "god" hypothesis applies equally as well to Zeus and Odin as it does to the Christian god; it applies equally well to evil or disinterested gods as it does to good gods. Thus even if we limit our consideration to the possibility of a god, ignoring every other random hypothesis, there's still no good reason to pick out any one god for favorable consideration.
What Does "God Exists" Mean?
What does it mean to exist? What would it mean if "God exists" were a meaningful proposition? For such a proposition to mean anything at all, it would have to entail that whatever "God" is, it must have some impact on the universe. In order for us to say that there is an impact on the universe, then there must be measurable and testable events which would 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 which requires some alleged "god" 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. It's technically true that the constant failures don't mean that no one will ever succeed, but it's even more true that in every other situation where such failures are so consistent, we don't acknowledge any reasonable, rational, or serious reason to bother believing.