Theists: What is the most compelling argument you have heard for Atheism?

[masterofpuppets]

The multiverse doesn't have to be finely tuned because it can be thought of as a kind of "foam" in which different "bubble" universes come to exist with their own physical constants. As aforementioned the multiverse was hypothesised based on our current understanding of physics, so it is at least somewhat viable in comparison to the idea that an intelligent designer did it.

As for the claim that if the physical constants were slightly different then our universe couldn't evolve to have structure, I agree with that completely, but it doesn't explain anything because it only applies to OUR universe. The fact that the physical constants are the way they are is a consequence of the fundamental nature of our universe, not the other way round, so by definition they can't be different. Constants don't give rise to universes, they are a property of universes. The nature of other universes could be so vastly different that they may have different constants, or they might not even have constants. The correct question to be asking is "how likely is it for a universe with structure and significant duration to come to exist" and sadly we just don't know the answer to this question.

The fine tuning problem also cannot explain why the universe appears to be overly tuned in some aspects. For example, the entropy at the instant of the Big Bang is many orders of magnitude lower than what it needs to be for the Stelliferous Era of the universe to last up until now. I would appreciate if any theist here could explain why God would need to fine-tune the Universe to an unnecessary extent.