Would the universe have played out differently?

Question

If the universe was rewound to an earlier point of time(to the beginning of the universe for example), would events have manifested exactly the same?

That is, would facts such as "[The Sun] formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud" or "Earth formed around 4.54 billion years ago" be true after 13.8 billion years had passed in the newly played out universe?

Would the randomness of stochastic events allow it to be manifestable that the factual history of the newly played out universe be divergent from ours?

I assume that the bare minimum satisfying the factual history of the newly played out universe departing from ours would be that a stochastic event after the point of rewoundment would occur differently than which occured in ours.

Thus, I assume, that the future of the newly played out universe could be vastly different from ours depending on when the first diverging stochastic event occured.

Answer 1

Physicists disagree, never mind metaphysicists.

The current standard understanding of quantum theory is that nature is inherently uncertain and probabilistic, so a second rerun would be almost certain to differ in detail, up to quite large scales inherited from the uncertainties inherent in the Big Bang and still visible across the night sky.

However some physicists believe, or suspect, that this uncertainty reflects our own ignorance of the true state of affairs; if we knew enough about aspects currently hidden to us, called "hidden variables", then the uncertainty would disappear. The universe would be found to be entirely deterministic after all, and any rerun would be expected to be identical.

The problem is that no such comparative rerun is logically possible, so it is in principle impossible to test which prediction is correct and the two positions are regarded as unscientific interpretations of quantum theory, as opposed to the theory itself.

Metaphysicians tend to pick and choose between such interpretations according to how they impact issues such as free will. For example physicist Hugh Everett posited a many-worlds theory in which a deterministic universe splits into multiple new universes every time a choice or an experimental observation is made. Thus, in any given timeline we appear to have free will. The idea appeals to those who seek some sense of free will in a deterministic reality, but it too is an unverifiable interpretation.

Answer 2

A question loaded with assumptions.

1. Your question carries the assumption that we know how variables behave along universe formation, so you ask what if we change one. This should be answered by you, according to the assumptions you are taking.

2. "the randomness of microscale events in the newly played out universe be non-negligible" assumes a subjective order of magnitude to make the difference: negligible to what degree? three atoms of difference is negligible? the existence of two stars? The results of a poll in USA? [1]

[1] Given that you use the term microscale, which is probably equivalent to thermodynamics microstate, I remember you that macrostates are subjective (e.g. temperature is basically a feeling). You suggest that even microstates change, macrostates might not. So, your measurement would depend essentially of subjective opinions. Think the consequences of such condition.

Answer 3

I tend to believe to the theory of Max Tegmark, that we live in mathematical universe. Which says that some mathematical structures exists, we don't know yet which mathematical structures are "basic", therefore existing, and which are "invented" by us. According to that theory, there is infinite number of possible universes, therefore our universe is, by anthropological principle, one of them, with laws of nature expectedly suitable for intelligent life.

Leopold Kronecker said that god created integer numbers, and everything else is created by man. According to that logic, only (positive?) integers are somehow bult-in into reality, in realm above and beyond "universes", perhaps because non-existence of integer numbers would cause some logical inconstancy.

From that point, we can assume, that any projection of integer set is equally "existent". Every way we look at existing object (integers) is equally "right" or "existent". Our universe, therefore, in its deepest level is mathematical function (projection) of integer numbers, which in turn, as an emergent by some additional projection can be perceived like "Level-3 multiverse" (Max Tegmark), which is multiverse of all Everettian possibilities of quantum interactions.

Note that in this model randomness is human invention, in nature itself there is nothing really random going on, only pseudo-randomness, like indexing problem, or insufficient knowledge / insufficient information.

Tegmark made great point, in my opinion, that function which defines laws of nature in our Level-4 universe is definitely "existant", because we can confirm its existence. But, if similar functions, with little bit different parameters or operators are non-existent, there would have to be some magic substance inside our particular mathematical function. That doesn't sound plausible. Also, we don't know what function define our mathematical universe, we are approaching it from two sides: Schrodinger equation and general relativity, but maybe it contain enormously huge numbers (constants) that we simply cannot ever derive from anything.

Side note: I'm sorry for not being yet allowed to comment/answer on your questions re this and other my posts.