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There is the specific universe we live in, the "actual" universe with planet Earth, humans evolving, and us discussing metaphysical debates on physics.se in 2012, etc. There might or might not also be other possible/potential worlds out there, some differing majorly, like in the laws of physics, or minorly, almost like our current world, but maybe I didn't pose this question on physics.se. According to many worlds advocates, the other possible worlds also exist out there in Platonic space. Is this world we find ourselves the only universe out there, or do other possible worlds also exist?

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Where's "out there"? –  Alfred Centauri Jul 14 '12 at 12:35
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Maybe you should have a look at this wiki page on Multiverses: en.wikipedia.org/wiki/Multiverse. Your question is not entirely clear though. –  ramanujan_dirac Jul 14 '12 at 13:40
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This is not a sensible question from the point of view of logical positivism, the answer is whatever you want it to be, or whatever is convenient for your current rhetorical purposes. –  Ron Maimon Jul 14 '12 at 21:31
    
Another metaphysical question. –  Anixx Jul 16 '12 at 22:46
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5 Answers 5

This question is a contradictionary question: An universe is a space-time with particles and energy etc. and it is an "invariant set", meaning that if you or any particle in this universe wander around you/it can never leave this universe. You and all energy and all particles will stay forever in this "box". If you where able to watch "thorugh a window" a second universe than it wouldn't be a second universe because photons or something you could watch was leaving the second universe. Therefore your universe (rather a sub-universe) is only an invariant sub-set of the "real" universe which is the unity of both. As the people in the second universe would classify your sub-universe not as "second" universe because particles or enrgy from their part can "wander" to your part.

The meaning of "universe" is that you mean the space-time for all particles and energy that exists in that way, that they may interact with particles or energy which possibly may interact with us. So the universe is the space-time and particles and energy which could be possible observed by us.

If there was an outer universe which contents we can not observe so how do you ever conclude its existence? This is an important statement of Karl Popper: Theories in science can be true or false but most importantly, you can test them whether they are true or false.

The outer-universe-theory is untestable because either you can test it (observe it) but than it is part of THE UNIVERSE or you can not observe it, than you cant test this theory and so it is not a physical theory.

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i was just watching this documentary when i saw your question. it explains the idea of a multiverse prediction as a result the inflation theory

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If there are multiple universe variants out there, then we have to ask, why are we in this particular universe and not some other universe? Why precisely like this and not that? Answers along the lines of well, it has to be one particular choice, are unsatisfactory and evades the question. This crops up in the many worlds interpretation. A way out is to propose this universe has consciousness, but the other universes don't.

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The issue hinges on co-existence. Can both our universe and some other universe co-exist? If universes interact so that they're observable, they probably co-exist, but even then, can we say for sure? But with decoherence, the many worlds of the many worlds interpretation decouple. The multiverses of eternal inflation lie beyond our cosmological horizon out of reach to us. So do they exist? The jury is still out on this.

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There are alot of theories to our "local universe".Many believe in the "big bang"which fits into the local universe model.Most now believe there are "blackholes"at the centre of each galaxy,galaxies join and so do blackholes forming larger and larger blackholes which over time become universe size blackholes,there are many of these outside of "our"universe which are pulling our universe in every direction.Each forming larger and larger blackholes the size of countless universes until over countless eons you end up with OMEGA a blackhole formed of all universes,so much matter it draws all to itself,Forming the one true singularity that finally can not contain any more that it "explodes"this is ALPHA"whitehole"it explodes with so much force that it travels faster than 'speed of light"that it is actually happened before it started and overlapps the old "multiverse",a continous cycle,the old becomes our "dark energy".we have been here many times before and as have other entities some who can step outside the cycle as we eventuallary do ourselves in our distant future,we now have future selves watching over us in energy form,look to the ionosphere we are there.haarp knows of this and so do nasa.;)

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this is nonsense. –  Ron Maimon Jul 15 '12 at 4:06
    
Yep Ron is right. –  Dilaton Jul 15 '12 at 23:01
    
AhAhAH, LOL, it's not physics but it is so hilarious as all the others 'Spiritism's, 'Multiverses', Darknesses and Blacknesses. They are adequate to Magic Minds and 'free lunchers'. They are the result and a measure of our total ignorance. This answers is a parody about all the nonsence I'm used to get in physics domain. The 'sunshaker' answer has the merit to recognize that a 'cyclic' universe makes sense. –  Helder Velez Jul 17 '12 at 2:10
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