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RE: Why the universe is most likely not infinite – Part 5: Popular argument against infinity
Very interesting.
This argument does not work quite as well as hoped, but the Big Bang is also not a proof of infinity and at least rules out an infinitely old, infinitely large steady-state universe.
This would be the case if you make the assumption that the universe started with the Big Bang. However, the Big Bang is not the origin of the universe, but the earliest state that we have evidence of. It is like the highest point of a mountain, which is not the beginning of the mountain, but the place where it starts to descend. The Big Bang describes how the universe evolved from an incredibly dense and tiny point, but it doesn't account for the laws of physics and other things. More and more cosmologists are moving away from the idea that the Big Bang was an absolute beginning and consider it a sort of "first moment of time", as Sean Carroll puts it.
I would say that this argument reminds me of another argument that apologists use to defend the existence of God using science to make philosophical points, such as in the Kalam cosmological argument. William Lane Craig is one of the main defenders of that argument but he was was critiziced by top physicists and mathematicians such as Sean Carroll, Roger Penrose, Carlo Rovelli, Adrian Moore and others on the plausibility that the universe may be eternal and and therefore, actual infinities may exist. The documentary is on Youtube.
Do you think the universe can be eternal? This, I think, brings many aporias.
If the past is infinite (rather uninitiated), we can go infinitely backwards, right? But if the past is infinite, it would take an infinity of time to elapse (the past), wouldn't it? But an infinite time would never end, precisely because it is infinite. However, the past has already end because we are, obviously, in the present. So, how can the universe be eternal?
Yeah, I'm pretty sure that's answered in the documentary too. You should watch it. There are several ways to approach it.
Given that there will be an infinite number of present times, then it is logically conceivable that an infinite amount of time has elapsed for each one of them. The limit of the past present time doesn't have to be the present time that you want to pick up, because that would be confusing and switching the necessary condition with the sufficient condition. I know, it gets confusing, that's how the logic works. This is only by resorting to Logic and Philosophy, not Physics. You can watch the documentary for more information.
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good point, at least we have good evidence of the Big Bang, but we have no idea what happened before the Big Bang and why it happened in the first place, but those questions are meta-physical, pure speculation, non-scientific in the sense that we cannot test theories that are outside of our universe.
I agree, but it's still mathematically consistent. Many cosmologists regard the Big Bang as an open boundary, so there are both models of the universe with a beginning and models of eternal universes. Also, as a general principle, metaphysics should conform to physics, so it's not unscientific necessarily. Anyway, the main point was that actual infinities might exist and it's a widely accepted view among the experts in the relevant fields. Thanks for bringing up this topic.