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Two entities truly captured within a singularity would have no positional offset from each-other, nor volume to differ either. Yet for two things to push away from each-other, they must have either volume or position for physics to determine which direction they should push each-other in. So it seems that because physics did decide which direction different entities would be expelled toward in the first instant of time after the big bang, the elements must have some positional offset from each-other.

Perhaps I haven't articulated this very well, but it just seems that for a singularity to expand, there must be some positional relationship other than zero in every dimension.

Even considering the HUP, I'm having trouble understanding it. Because HUP's behavior can be demonstrated in Feynman diagrams, but I don't think those diagrams support two entities trapped in zero volume and zero offset. There's always a positional relationship involved in the interaction, and it seems this is built into the very way physics works.

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  • $\begingroup$ What is HUP? ????? $\endgroup$
    – garyp
    Aug 6, 2021 at 0:20
  • $\begingroup$ @garyp unfamiliar with heisenberg uncertainty principle? $\endgroup$
    – J.Todd
    Aug 6, 2021 at 0:42
  • $\begingroup$ I've been a physicist for 45 years, and I never heard it referred to as "HUP". Best not to use acronyms unless they are extremely common. People have different experiences. $\endgroup$
    – garyp
    Aug 6, 2021 at 10:32
  • $\begingroup$ @garyp long name to type out every time. $\endgroup$
    – J.Todd
    Aug 6, 2021 at 11:46

2 Answers 2

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One needs to be very careful when thinking about the "expansion" of the universe from the Big Bang. There is no pre-existing space for the singularity to expand into, and therefore the use of terms like "push away" from each other have little meaning. The expansion of the universe is determined by the properties of the metric. Two particles theoretically existing within the singularity never move away from each other. Rather, it is the fabric of space and space-time that changes as determined by the properties of the metric resulting in what we experience as an expanding universe.

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  • $\begingroup$ That's an interesting thought. Even so I still see an issue. Let's simplify this to a two-body problem. There's a singularity before the big bang with two bodies, whatever they are. Now space expands between them. Simple enough. But wait, there's a third body. A new kind of three body problem: How does nature decide which direction space has spread between the two and this third body? Above or below them? Ah, to the three bodies there is no above or below to refer to. But to the fourth and fifth bodies it certainly matters. $\endgroup$
    – J.Todd
    Aug 6, 2021 at 1:03
  • $\begingroup$ I don't think specifying that "space is getting changed by the properties of the metric" rather than "objects are moving away from each other" addresses the question. $\endgroup$
    – Señor O
    Aug 6, 2021 at 1:31
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    $\begingroup$ @SeñorO thinking it through, I guess it's nothing more than a perspective shift, where you consider the question as an observer outside of space vs an observe in it. $\endgroup$
    – J.Todd
    Aug 6, 2021 at 2:13
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Very simplified version of what you may want:

Firstly, the universe is expanding constantly.

Secondly, we know this because of the Doppler effect, where objects that are further are red-shifted, whereas objects nearer are blue-shifted.

Therefore (there is more to this), objects are not actually moving apart, the addition of extra "space" (due to uniform expansion) in between galaxies causes the illusion of them moving apart.

Extension:

Also, extending the possible expansion theorem above, we do not know when the universe began (guesses are about 13 billion years ago but it keeps increasing) or how it began... The universe astronomers and scientists currently are aware of it the observable universe (about 96 billion light years in diameter). The universe could be much bigger than that (possibly infinite).

To understand the Big Bang, first astronomers and scientists in the past used light to calculate the position of celestial objects far away and even though light travels very fast, it's still take a very very very very very long time to reach us.

Taken into a inverse perspective: If a person 70 million light years away is looking towards Earth right now, they would be seeing the dinosaurs because the light currently reaching them took 70 million years to travel and carried information from approximately 70 million years ago.

Now if we looked at a galaxy 2 billion light years away, it does not define what or where the galaxy is now, but instead what and where it had been 2 billion years ago.

Now back to the Big Bang. Seeing as we have potential data from eons ago, scientists and astronomers used this to approximately calculate the age of the universe and what it might have been like.

The universe coming from a point of singularity is similar to saying black holes are mini-verses. Although the statement is not false, you might what to prove it by some form of proof (search google maybe).

I know this is not directly answer your question but see if it helps anyway.

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