I have heard some theories that the Big Bang could be possible due to the way quantum mechanics work, which would allow for empty space and matter to be created out of nothing. What are your thoughts on this? Do these theories rely on circular reasoning?
There are highly speculative theories—so speculative so as to not really even deserve the label scientific “theory” that the universe itself could be created from some sort of vacuum—out of nothing. This theory uses as support the fact that quantum mechanics predicts the temporary production of particles from empty space. This second claim of quantum fluctuations in the universe is consistent with evidence, and is therefore a good scientific theory. The idea that the universe itself was created as some sort of incredibly massive quantum effect is not even a scientific theory. It is mere speculation and speculation of the most unreasonable sort in my opinion. Any scientific theory which deserves the name must be both testable by experiment and refutable by experiment. This theory of the quantum creation of the universe is neither testable by experiment nor is it refutable. It therefore does not deserve to be considered as a scientific theory of creation of the universe.
Besides, the argument is that the quantum creation of the universe is somehow analogous to the quantum creation of particles out of space is simply NOT TRUE. The creation of particles by random quantum fluctuations is something created out of something. Space is a thing in the quantum view, and it is the thing from which these particles appear to come. The speculation of the creation of the universe itself as a quantum fluctuation is a theory of creation of something out of literally nothing. This is NOT analogous to the quantum fluctuation theory at all. With the big bang, there is no space out of which it can fluctuate randomly. What is the “thing” from which this quantum fluctuation came? This theory begs the question. It involves an unprovable assumption which violates the law of cause and effect.
Whether this theory relies on circular reasoning will depend on who is doing the reasoning. For example if this theory is used as “proof” that God does not exist, then it is clearly circular reasoning, but if it is used merely as an attempt to explain the existence of the physical universe, then it may not be circular reasoning, but it is using blind speculation and should not be presented as a solid scientific theory, as it amounts not only to speculation about physical things, but is in fact a philosophical speculation—one which most scientists are probably not even equipped to make.