Separation of Multiple Universes?

  • #1

Main Question or Discussion Point

Assuming that theories regarding the existence of multiple universes are true, what would separate said universes? If multiple universes exist, it can be assumed that there is some form of separation between said universes. This could be in the form of a barrier, or a kind of "space" between the universes, or both. Has there been any serious speculation regarding the topic of what exactly separates these universes?
 

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  • #2
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There has been a good deal of research into such ideas... the first stumbling point is semantic, what exactly distinguishes multiple universes from one larger universe. I'm only familiar with eternally inflated (multi)verse theories--so my response will be relative to those.

A 'universe' (in this context) is a causally isolated region of space, i.e. it has an event horizon. This is consistent with observations, as we believe there is an event horizon at about 13.7 billion light years from us. According to eternal inflation theories, there are an infinite number of other universes out there, outside our horizon, separated from us by normal old space (which may or may not be rapidly inflating---causing or perpetuating the horizon at some point in history). There would be no 'barrier' per se, but the gap is fundamentally untraversable.

Again, I'm not very familiar with most other multiverse theories, but presumably our 3+1 dimensional universe is embedded in a higher dimensional space, and thus a 5th (e.g.) dimension separates numerous 3+1 dimensional universes.... perhaps.

Hope that helps.
 
  • #3
bcrowell
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I agree with zhermes that this depends a lot on what you mean by multiple universes.

If you're talking about the many-worlds interpretation of quantum mechanics, then there is no separation at all. They're superposed waves.

In the context of baby universes (e.g., Smolin's cosmological natural selection), I think the baby is typically imagined as being a separate spatial manifold for a given surface of simultaneity, so that there is no space or anything else physically separating the parent and daughter universes -- they're just causally disconnected spacetimes.
 
  • #4
Chronos
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The notion of 'multiple' unverses is illogical, IMO. If they are causally disconnected, they are not observationally relevant. If not causally disconnected, they are part of our observationally accessible universe - i.e., you cannot have your cake and eat it too.
 
  • #5
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Since learning about causually disconnected universes beyond our own observable universe I am convinced that not only do they exist but that they are separated from us by the fact that they are flying away from us at superluminous velocities. That surely is a wall of separation that can never be breached with anything physical in this universe.
 
  • #6
bcrowell
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The notion of 'multiple' unverses is illogical, IMO. If they are causally disconnected, they are not observationally relevant. If not causally disconnected, they are part of our observationally accessible universe - i.e., you cannot have your cake and eat it too.
For a counterexample, see Smolin's cosmological natural selection, which is a multiple-universe theory that makes testable predictions, and that was in fact falsified last year by observation, 18 years after it was proposed.
 
  • #7
Chronos
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For a counterexample, see Smolin's cosmological natural selection, which is a multiple-universe theory that makes testable predictions, and that was in fact falsified last year by observation, 18 years after it was proposed.
Am I correct in assuming you are refering to detection of high mass neutron stars?
 
  • #8
bcrowell
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Am I correct in assuming you are refering to detection of high mass neutron stars?
Yes.
 
  • #9
There has been a good deal of research into such ideas... the first stumbling point is semantic, what exactly distinguishes multiple universes from one larger universe. I'm only familiar with eternally inflated (multi)verse theories--so my response will be relative to those.

A 'universe' (in this context) is a causally isolated region of space, i.e. it has an event horizon. This is consistent with observations, as we believe there is an event horizon at about 13.7 billion light years from us. According to eternal inflation theories, there are an infinite number of other universes out there, outside our horizon, separated from us by normal old space (which may or may not be rapidly inflating---causing or perpetuating the horizon at some point in history). There would be no 'barrier' per se, but the gap is fundamentally untraversable.

Again, I'm not very familiar with most other multiverse theories, but presumably our 3+1 dimensional universe is embedded in a higher dimensional space, and thus a 5th (e.g.) dimension separates numerous 3+1 dimensional universes.... perhaps.

Hope that helps.


Why are you using the term event horizon? if every black hole has an event horizon, and there are many black holes in our universe, does that not mean that the number of event horizons = the number of black holes. when i read your answer, it sounds like the expanding edge of the universe (if it is expanding) is a black hole.
 
  • #11
the use of the phrase 'event horizon' can be correct. has anybody proved/disproved whether we are actually a singularity ourselves. nobody really knows the physics of inside a black hole where time and space are different (or same, no-one knows) compared to the outside. my point being, (almost) every term and every physical outcome may be possible until proved otherwise (assuming the mathematics holds aswell).
 

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