There’s going to be some physics talk here, but it’s important to remember this is primarily a philosophical argument over a question of reality and proper definition.
Being primarily mathematical in nature, I’ve encountered no good reason to believe that the second law of thermodynamics does not apply to the big bang in the same way that it applies to other, observable singularities in the universe. Namely, black holes.
Restating in my own words, the second law holds that in a closed system heat will become more distributed over time, and never less. As a consequence, over time everything in the closed system must eventually regress to the average temperature of the system. After infinite time, all deviations must be due to statistical fluctuations rather than order.
We have no physical reason to believe that the universe we inhabit is an open system that receives matter, heat, order, information or any inputs at all from outside. (If it did, we’d be forced to accept that there are at least two universes, one of which has causal influence over our own. I’ll leave that train of thought at the station for now.) We recently witnessed a controversy in the field of physics that claimed some of our matter was disappearing through black holes without any equivalent replacement. This would have indicated that the second law breaks down at a singularity.
Thanks to Stephen Hawking and Roger Penrose, we now know that black holes do replace the matter they gobble up through Hawking radiation. It seems that quantum mechanics allows statistical freak particles to tunnel past the event horizon, temporarily exceeding the speed of light. This means that, as I said before, the second law is still true inside a singularity.
By all accounts, the universe is still a closed system. Even before the Big Bang occurred and all matter was contained in a tightly packed soup of energy and quantum mechanical madness, before gravitational and eletromagnetic and nuclear forces existed, before the universal constants of classical mechanics had definitions, before “spacetime” itself existed, the second law of thermodynamics was apparently still true.
While it’s difficult to talk define time in a singularity, it’s important to note that infinite time cannot have passed since any particular singularity. Else all the universe would have regressed to the mean temperature of the closed system, allowing only statistical variation. This is not the case in the universe we observe, which has lots of open space at a near constant temperature and sharp discontinuities at stars, black holes, planets, and other congregations of matter.
This is true even if this is not the first universe to have existed. Say all the matter of some portion of a previous universe had gravitationally collapsed into the singularity known as the big bang. And if time has no beginning, this must happen an infinite number of times: All matter must eventually condense, expand into infinity, or hold in perfect stasis between balanced forces. The matter in our universe is probably split in this regard, with galaxies splitting into island universes that drift away from each other into infinity.
This leads to the same eventual fate as the second law predicted. None of the derivative universes can contain more matter than the previous universe, which means that entropy has increased as expected. Over infinite time, entropy still reaches a maximum through this process. And we can observe that this is not the case.
So the argument, in summary, is this:
- There was no location in the causal history of the universe during which the second law of thermodynamics did not apply.
- If causality has no beginning, then entropy must be at a maximum.
- Entropy is not at a maximum.
- Therefore, causality has a beginning. (I.e. The universe was not always a closed system.)
I did some baiting and switching between “causality” and “time” in the physical descriptions in support of the first statement, but I don’t think I violated the logic. (I assume time is merely a series of material interactions.)