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Thread: Understanding the Multiverse Theory

  1. #1 Understanding the Multiverse Theory 
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    Hi Everyone,

    I'm a physics layman and was curious if ya'll can help explain to me in simple to understand terms what this theory is all about.

    First of all, is the cosmology/physics theory of the multiverse the same as this new-age religion theory of the multiverse where one decision affected the entire universe and there is another universe in which someone still lives in had that someone made a different decision? Ex) You and I are sitting on the sofa, we go outside, I get bite by a dog. That's one universe. In another universe, you and I are still sitting on the sofa, we decide not to go outside, I don't get bite by a dog, we watch football instead.


    My second question, if there is a difference, is the cosmological/physics theory of the multiverse saying that multiple universes/entire cosmos have banged and crunched many times before and we are now alive in this current bang or is it saying that we have many, many universes/cosmos going on at the same time right now. Hope this makes sense.

    Thanks to all that reply.


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  3. #2  
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    Quote Originally Posted by Tau Ceti View Post
    First of all, is the cosmology/physics theory of the multiverse the same as this new-age religion theory of the multiverse
    No.
    It's a scientific interpretation, a possible explanation of quantum mechanics.

    My second question, if there is a difference, is the cosmological/physics theory of the multiverse saying that multiple universes/entire cosmos have banged and crunched many times before and we are now alive in this current bang or is it saying that we have many, many universes/cosmos going on at the same time right now.
    All "going on now".


    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
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  4. #3  
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    Quote Originally Posted by Tau Ceti View Post
    I'm a physics layman and was curious if ya'll can help explain to me in simple to understand terms what this theory is all about.
    There are several different theories (speculations or hypotheses might be more accurate) that could be described this way. For example, there is "Eternal inflation" which proposes that there are "big bangs" happenign continuously in different places, creating new universes. There are extensions of string theory which suggest our universe may be part of a higher dimensional "brane space". And many others I am even less familiar with.
    Eternal inflation - Wikipedia, the free encyclopedia
    Brane cosmology - Wikipedia, the free encyclopedia
    Multiverse - Wikipedia, the free encyclopedia

    First of all, is the cosmology/physics theory of the multiverse the same as this new-age religion theory of the multiverse where one decision affected the entire universe and there is another universe in which someone still lives in had that someone made a different decision?
    This sounds like a version of Everett's Many Worlds interpretation of quantum mechanics. This is an alternative to things like the Copenhagen Interpretation and others. Rather than an observation collapsing the wave function (the Copenhagen view) it says that all possibilities exist as separate parallel worlds. Nothing to do with the multiverse. And not a theory - just a different view of the same underlying theory.
    http://en.wikipedia.org/wiki/Many-worlds_interpretation

    My second question, if there is a difference, is the cosmological/physics theory of the multiverse saying that multiple universes/entire cosmos have banged and crunched many times before and we are now alive in this current bang or is it saying that we have many, many universes/cosmos going on at the same time right now.
    Either and/or both of the above!
    ei incumbit probatio qui dicit, non qui negat
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  5. #4  
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    Quote Originally Posted by Tau Ceti View Post
    Hi Everyone,

    I'm a physics layman and was curious if ya'll can help explain to me in simple to understand terms what this theory is all about.

    First of all, is the cosmology/physics theory of the multiverse the same as this new-age religion theory of the multiverse where one decision affected the entire universe and there is another universe in which someone still lives in had that someone made a different decision? Ex) You and I are sitting on the sofa, we go outside, I get bite by a dog. That's one universe. In another universe, you and I are still sitting on the sofa, we decide not to go outside, I don't get bite by a dog, we watch football instead.


    My second question, if there is a difference, is the cosmological/physics theory of the multiverse saying that multiple universes/entire cosmos have banged and crunched many times before and we are now alive in this current bang or is it saying that we have many, many universes/cosmos going on at the same time right now. Hope this makes sense.

    Thanks to all that reply.
    Welcome Aboard, Tau Ceti.

    The Multi-verse idea is not a "Theory." It is a hypothesis- at best.

    The basic idea is that any in-determinant outcome simultaneously exists in both states until the outcome is determined, collapsing it to one state. (Edit: Strange expanded on that much better than I did. I hate you Strange. <Shakes fist. 'Wernstrom!!'> )

    Personally, I find the hypothesis to be... Imaginative and rather too literal.

    Unlike Relativity, Evolution, The standard model, etc, Multiverse or Brane is not supported by a good set of observational and experimental evidence.

    Even "String Theory" is not a theory. It is a hypothesis that is mathematically very interesting, incomplete, and not supportable by experimentation at this time.
    If you want details on String- ask someone else. It's way over my head...
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  6. #5  
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    If it's all going on now, where are these other universes? Are these other universes something we can actually detect?

    Also, does this multiverse idea butt heads with the idea that our universe is the only universe created from the singular Big Bang or is there some sort of reconciliation between the two that I'm ignorant of?

    Thanks again.
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  7. #6  
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    Quote Originally Posted by Tau Ceti View Post
    If it's all going on now, where are these other universes? Are these other universes something we can actually detect?
    In the case of the many worlds interpretation, I'm not sure how literally it is supposed to be taken. The "other worlds" can never be detected because that would make it a different theory from the underlying theory of QM. If they can't ever be detected, the word "exists" doesn't really seem relevant.

    In the case of cosmological theories, there are suggestions we could detect some very faint interactions between other universes but this is still highly speculative.

    Also, does this multiverse idea butt heads with the idea that our universe is the only universe created from the singular Big Bang
    Strictly speaking, the big bang theory doesn't say anything about "creation of the universe" - it is purely about the evolution of the universe from an earlier hot dense state. It also doesn't require there to be only one; the eternal inflation idea is just one (of many) variant of big bang cosmology.
    ei incumbit probatio qui dicit, non qui negat
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    Hello,

    I don`t know much about those "cosmologistic" multiverses, branes and such. For computational purposes only it is very convenient to assume many worlds interpretation of quantum mechanics. One can avoid uneccesary mistakes computing amplitudes especially in quantum optics.
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  9. #8  
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    Quote Originally Posted by Tau Ceti View Post
    First of all, is the cosmology/physics theory of the multiverse the same as this new-age religion theory of the multiverse
    If there really is a new-age woo version of Everett's idea then it is strangely ironic because (as I understand it) one of the strengths of this interpretation is that it gets rid of the idea that an "observer" collapses the wave function. And, of course, the woo-meisters, love to insist that the "observer" must be a conscious observer and therefore "we create the universe" (if we do, couldn't we make a slightly better job of it?)
    ei incumbit probatio qui dicit, non qui negat
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  10. #9  
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    In The Hidden Reality Brian Greene discusses 9 different versions of Multiverse hypothesis. If you don't like any of those, you can probably make up your own.
    Neverfly likes this.
    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
    Philosophically more pleasing, more psychologically easy
    Prof Richard Feynman (1979) .....

    Das ist nicht nur nicht richtig, es ist nicht einmal falsch!"
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  11. #10  
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    I'm getting the feeling that the multiverse is more of just a hypothesis/fun idea. Correct?

    If that is the case, would you guys say that our cosmos is indeed the only cosmos out there and the only one ever created/existed?

    Is the evidence pointing more strongly towards the idea that our universe did indeed begin to exist and has only been in existence once?
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  12. #11  
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    Quote Originally Posted by Tau Ceti View Post
    I'm getting the feeling that the multiverse is more of just a hypothesis/fun idea. Correct?If that is the case, would you guys say that our cosmos is indeed the only cosmos out there and the only one ever created/existed? Is the evidence pointing more strongly towards the idea that our universe did indeed begin to exist and has only been in existence once?
    "The multiverse" is actually ill-defined; there are many multiverse ideas out there. But if we are talking about Everett's multiverse interpretation of QM, it is precisely that: An interpretation. As Everett points out in his PhD thesis, this interpretation is experimentally indistinguishable from, say, the Copenhagen interpretation version of QM (because these other universes are orthogonal -- not parallel -- to ours). So, while QM is certainly a theory, Everett's multiverse is not. There is no experiment, no test that one could perform to falsify it. In that sense, Everett's multiverse interpretation is aimed at human psychology. As for your other questions, there is no evidence of other or prior universes. That's all we can say. Until such evidence emerges, Occam suggests we proceed for now as if no such universes exist or have existed There's no reason to complicate things, so until we're given a reason, we'll keep it as simple as possible, while maintaining consistency with evidence.
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    If there is no evidence for a prior universe or other universes, then this should stop the idea of a multiverse in it's tracks, since it is not detectable.

    So, bottom line...our universe is not eternal, we are the only universe/cosmos that we know of, and it definitely began with the Big Bang. Correct?

    Thanks again to all of you guys.
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  14. #13  
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    Quote Originally Posted by Tau Ceti View Post
    If there is no evidence for a prior universe or other universes, then this should stop the idea of a multiverse in it's tracks, since it is not detectable.
    The fact that we don't currently have any evidence doesn't mean that people shouldn't use existing theory to come up with possibilities. Some of those might be testable and give us some evidence one way or the other.

    So, bottom line...our universe is not eternal
    Not known. It might be or it might not. It might have had a beginning or maybe not. If it had a beginning, it might still last forever.

    , we are the only universe/cosmos that we know of, and it definitely began with the Big Bang. Correct?
    We have no idea about any "beginning". Again, there is speculation that the universe could have "begun" at some time but there are also theories that say it has always existed.
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    Oh boy....these competing theories of cosmology is a lot like an atheist vs christian debate. Two sides butting heads using what they each call evidence for their position.

    If our universe, the one we know now and exist in now, "began" or evolved, as Strange kindly educated me, then our universe could not be eternal because if it were eternal then it should have evolved past our current state by now. Maybe I'm lacking some info. here that's hindering my understanding though.

    On the flip-side, if our universe is eternal, then it would have already expanded and ran out of energy by now, wouldn't it? Thus, it "began" to exist. But, I'm hearing that there are theories/hypotheses saying it can be eternal but if so, then we're back to my first paragraph in this post. I'm just a layman talking. Do correct me and provide input without hesitation.

    I know this part was a bit off topic but thanks for hanging in there with me. This is really important to me personally so I hope ya'll don't mind the multiple questions.
    Thanks to all who replied.
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  16. #15  
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    Quote Originally Posted by Tau Ceti View Post
    On the flip-side, if our universe is eternal, then it would have already expanded and ran out of energy by now, wouldn't it? Thus, it "began" to exist. But, I'm hearing that there are theories/hypotheses saying it can be eternal but if so, then we're back to my first paragraph in this post.
    Well one possibility is that there was a "big bounce" rather than a big bang: an infinitely repeating series of cycles of expansion and collapse. This was the default assumption until observation appeared to contradict it. There are also models that put the big bang an infinite time in the past.
    ei incumbit probatio qui dicit, non qui negat
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  17. #16  
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    Quote Originally Posted by Tau Ceti View Post
    If it's all going on now, where are these other universes?
    That's like asking where is the future.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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  18. #17  
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    WARNING: The following is how I understand the multiverse, which may differ from how others understand it.

    The multiverse is a configuration space. That is, it is the set of all possible realities, which may be taken to mean entire histories. There is nothing new about the notion of a configuration space. The notion is implicit in Lagrangian mechanics and the calculus of variations, both which date from no later than the 18th century. The idea is that although there is only one version of any configuration of the entire history of reality, many versions do share the same configuration of parts of entire history of reality. This means that there are many versions of the same entire history of the universe up to this time which differ only at some point in the future. Quantum mechanics is based on the notion that while we have a choice to measure a wide variety of observables, these observables are not necessarily compatible with other, such that causing one observable to take on a specific value causes some other observables to take on a multiplicity of values. This is the Heisenberg uncertainty principle. For example, an audio waveform cannot have both a definite location in time and a definite frequency, frequency and time being incompatible (for mathematical reasons). This forces us to conclude that each of the configurations of reality exist in a real sense because a single configuration in itself violates the Heisenberg uncertainty principle.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by Tau Ceti View Post
    If there is no evidence for a prior universe or other universes, then this should stop the idea of a multiverse in it's tracks, since it is not detectable.
    "No evidence" does not necessarily equate to "not detectable." And Everett's multiverse interpretation says nothing about prior universes. You were not specific about what multiverse ideas you meant. I talked only of Everett's. In his multiverse interpretation, the other realities that fork at each juncture are forever "lost" in the sense of not being detectable. Since his interpretation does not enhance QM's predictive power, it has somewhat fallen out of favor with most mainstream physicists (at least the ones I know).

    So, bottom line...our universe is not eternal, we are the only universe/cosmos that we know of, and it definitely began with the Big Bang. Correct?
    Bottom line is actually that we only know of one universe. We don't know anything about its beginning, however. The BBT is a theory of evolution, not of creation (despite what you may have read in the popsci literature). We know that the universe was once denser and hotter than it is now. That's not quite the same as asserting that it "definitely began" with the BB. We do not have a mathematically self-consistent, rigorous theory that extends that far back. So the only honest answer is "we don't know how it began." Since we don't know that, we certainly don't know what went before.
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