Yazata: Obviously, if time itself ceases to exist in any form once we rewind to the big bang, then the notion of causality also vanishes at that point. In that case, asking "What caused the big bang?" is kind of like asking "What is north of the North Pole?" You're right, though, that many (perhaps most) cosmologists are not satisfied with this. This is why some speculate that there are physical laws and principles that operate beyond the bounds of the space and time that we find in an individual universe. Some suggest that our universe might, in fact, be part of a much larger "multiverse" consisting of many separate universes. Perhaps the "other" universes are like ours, or maybe they differ in various ways (e.g. in the values of certain "fundamental" constants of nature, perhaps). This is all speculation. Even the idea that time began at the big bang is speculative, because our current theories can't say for sure what happened in the earliest epochs. Maybe time is somehow continuous, in a sense. Stephen Hawking in his Brief History of Time, suggests, for example, that "imaginary time" (where "imaginary" is used in a technical, mathematical, sense) might link consecutive instances of an oscillating universe. We don't necessarily have to dispense with physical reality. A multiverse model, for example, still has lots of physical "stuff" in it - perhaps uncountable "bubble" universes, which might pop up for a while then die off again several billion years later (sometimes much quicker, sometimes not so quick). If our own universe is just one "bubble", there's no need to invoke metaphysical Platonic forms to explain it. We only need to throw out the idea that our observed universe is in some sense special in containing space, time, matter and energy. Both physicists and mathematicians differ in their personal points of view on this question. Valenkin, seen in the video in the opening post, appears to be (perhaps) a believer in eternal Platonic forms, or something like that, though it's hard to tell from what he says there. Others agree with him. On the other side of the fence, though, I think you'll find equal numbers of physicists and mathematicians who regard mathematics as a human-created descriptive tool. There remains some mystery about why mathematics applies just as well as it does to describing our physical world, because there's no a priori reason for us to assume that should be true. Speaking personally, I do not believe that the elements of mathematics exist in some kind of ideal realm, separately from the human beings who think about them. But that's just my personal opinion. From my point of view, while mathematics is amazingly useful, the further we dig into physical reality the harder it seems to be to apply our mathematics to describing it. Things get mathematically messy very quickly as we drill down. There's not a perfect match between neat maths and neat physics. In fact, I'd say that we put certain strains on our mathematics when we use it to describe certain kinds of physical phenomena, to which it perhaps is not well suited. Newton was a Christian, convinced that the bible held arcane secrets etc. Einstein, on the other hand, claimed to believe in "Spinoza's God", by which he seems to have meant the total impersonal collection of fundamental physical principles etc. Einstein's statements about the "mind of God" and the like can be read as talking about the principles of the natural world; "God" was just a shorthand for nature's laws, for him.