Carl Sagan: The answer depends very much on what we mean by God. The word "god" is used to cover a vast multitude of mutually exclusive ideas. And the distinctions are, I believe in some cases, intentionally fuzzed so that no one will be offended that people are not talking about their god.
But let me give a sense of two poles of the definition of God. One is the view of, say, Spinoza or Einstein, which is more or less God as the sum total of the laws of physics. Now, it would be foolish to deny that there are laws of physics. If that's what we mean by God, then surely God exists. All we have to do is watch the apple drop.
Newtonian gravitation works throughout the entire universe. We could have imagined a universe in which the laws of nature were restricted to only a small portion of space or time. That does not seem to be the case. And Newtonian Gravitation is one example, but quantum mechanics is another. We can look at the spectra of distant galaxies and see that the same laws of quantum mechanics apply there as here. So that is itself a deep and extraordinary fact: that the laws of nature exist and that they are the same everywhere. So, if that is what you mean by God, then I would say that we already have excellent evidence that God exists.
But now take the opposite pole: the concept of God as an outsize male with a long white beard, sitting in a throne in the sky and tallying the fall of every sparrow. Now, for that kind of god I maintain there is no evidence. And while I'm open to suggestions of evidence for that kind of god, I personally am dubious that there will be powerful evidence for such a god not only in the near future but even in the distant future. And the two examples I've given you are hardly the full range of ideas that people mean when they use the word "god".
---The Varieties of Scientific Experience
- What is your take of the idea of "god" ?