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If there are people in other universes, and they are watching the Big Bang that created ours. What will they see?
Answer 1:

Well, that depends on how time works in the universe of that people, and if it is similar or different to time in our universe.

However, here is something to consider: a location called a singularity exists at the center of a black hole, where the forces involved become infinite, and space and time come to an end. If you were to fall into such a black hole (and somehow not be torn apart by the tidal forces), you would reach the singularity in a finite period of time, at which point time itself would, literally, end.

Now, black holes have event horizons (an event horizon is a boundary in spacetime beyond which events cannot affect an outside observer) that hide the singularities and what goes on around them from the outside. However, there may be objects in the universe called naked singularities - essentially black holes but without event horizons. If you were to see something else falling into a naked singularity, then you would notice that it would slow down and slow down and never actually reach the singularity, unless of course you were falling in yourself, in which case you would get there at the same time as the other object, even if it had been falling in ahead of you.

The Big Bang was a singularity, just of the opposite type, with space, time, matter, and energy coming OUT of it instead of falling in. Relativity implies that a singularity like the Big Bang could not directly be observed in the same way that the singularity of a black hole could not directly be observed, event horizon notwithstanding: you would notice time speeding up for objects coming out of a singularity like the Big Bang, instead of time slowing down for something falling into a black hole.

Now, IF there are other universes, AND they can see into our universe, and their time works like ours, then they would have to obey relativity just as we do and what I described in the previous paragraph is what they would see. However, if they really are in a different universe, there is no reason why the physics of their universe would need to be anything like our physics: time might work entirely differently, not even be the same thing, or, for that matter, time might not exist at all for them. Until WE can actually observe said other universes, then there is no way that we could know anything about what their physics are like.

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