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Can other universes exist?

  1. Aug 21, 2013 #1
    Can other universes exist? Can they have different laws of physics and/or different laws of math than our own universe?
     
  2. jcsd
  3. Aug 22, 2013 #2

    Chronos

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    Where? The universe is, by definition, everything causally connected to our universe.
     
  4. Aug 22, 2013 #3
    In my opinion the best case for other universes is presented by Alan Guth here:

    http://arxiv.org/abs/hep-th/0702178
    But we dont know for sure that inflation happened (so far the evidence loos pretty good but the slam dunk of gravity waves has not yet been seen).

    Even if inflation did happen there's still the possibility of Guth being wrong about the way the inflaton field evolves.
    There are other arguments that i find less convincing like the many worlds interpretation of Qm and string landscape.

    So I think the answer is yes they (possibly) can exist, but we cannot say that they do exist.
     
  5. Aug 22, 2013 #4
    I supect the answer to the OP's question is unknowable.
     
  6. Aug 22, 2013 #5

    phinds

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    Not necessarily. He asked "can" they exist which MIGHT be knowable, not "do" they exist, which I agree is almost certainly unknowable.
     
  7. Aug 22, 2013 #6
    I think there is some hope for progress. We might be able to see some signature of eternal inflation in the CMB. Or maybe theorrists can improve our understanding of inflation and show whether it is eternal or not. Perhaps some new theorretical framework will give us inflation without eternal inflation. Marcus think this is is the case with some forumaltion of LQC , but I'm not so sure its in all forumulations.
    Maybe inflaiton will be shown to be false. This wont disprove the multiverse but it will take the most plausible argument for it away IMHO
    Im not holding my breath for any of these but I dont see any reason to give up on increasing our knoweldge.
     
    Last edited: Aug 22, 2013
  8. Aug 22, 2013 #7
    Hmm. I'm guessing that while different universes could possibly have different laws of physics, the laws of math would be the same in all of them. Two plus two will always equal four, never five.
     
  9. Aug 22, 2013 #8

    phinds

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    Yes, since math is an internally consistent construct developed by man and divorced from physical reality (although it does a TERRRIFC job of describing lots of reality as we understand it) it would be independent of physical laws.
     
  10. Aug 22, 2013 #9
    Many worlds interpretation of QM comes to mind. But if the universe is infinite in size, could there exist any other universe?
     
  11. Aug 22, 2013 #10
    Yes, and I can give you a perfectly reasonable scenario under which that would happen. At present we do not understand how our Universe came in being. One possibility however which fits current observations is through a phase-transition. An analogy here would be helpful. Consider water. As we lower the temperature and reach the freezing point, it undergoes a phase-transition from liquid to solid. The freezing point is a critical point in the dynamics of the water.

    We observe many phase-transitions in Nature and often these changes are accompanied by likewise qualitative changes in the rules, or laws which describe the phenomenon: the rules on one side of the critical point are different than the rules which describe the phenomenon on the other side of the critical point. For example, the concept of swimming looses meaning at the freezing point of water as fluid-dynamics are replaced by solid-state dynamics.

    And so if the Universe was born as a critical-point transition of some larger dynamic system, a pre-existence we can call it, and if that pre-existence has multiple critical points, then I do not think it is unreasonable to suggest had it transitioned through a different critical-point, the resulting Universe might be very different from ours including the prospects of having qualitatively different physical laws.
     
    Last edited: Aug 22, 2013
  12. Aug 22, 2013 #11
    of course they can, there aren't any physical laws that would forbid them, the real question is if they do
     
  13. Aug 23, 2013 #12

    Chronos

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    The same applies to refrigerator light fairies. It's a cart full of imagination and crap.
     
  14. Aug 23, 2013 #13
    jackmell, I disagree for the following reason...

    Using your analogy of phases of mater; solid, liquid, and gaseous water all obey the same fundamental laws of physics. If the laws of physics that we observe and measure in our universe are different then those in another universe then none of them are actually fundamental laws of physics but rather different manifestations of deeper laws which are universal. (or multiversal) :-)
     
  15. Aug 23, 2013 #14

    That would lead to another question. Could the laws of physics be different in different areas of a single universe, maybe even our own universe?
     
  16. Aug 24, 2013 #15
    I think the whole question of other universes turns on the idea of there being a boundary to our own (and of course that begs the notion of 'neighbours') - and it's a question that's been documented at least since the Middle Ages and doubtless, long before that too.
    But to my mind, it's an absurdity at a level too profound to be resolved ... that is until we've answered a LOT more questions.
     
  17. Aug 24, 2013 #16
    There is nothing magical or supernatural about the conditions that gave rise to life in the solar system - they can all be physically defined.
    And when you understand that there are 3-400 billion stars in the Milky Way and at least the same number of galaxies in the observable universe, you begin to realise the immense probability of similarly conducive conditions existing elsewhere in the Milky Way alone.
     
  18. Aug 24, 2013 #17

    phinds

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    This has NOTHING to do with the statement that you quoted this as a response to.
     
  19. Aug 24, 2013 #18

    phinds

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    No that is not true at all. Multiverse theories do not require our universe to be either finite or bounded.
     
  20. Aug 24, 2013 #19
    May I ask why you dispute that? Is there any scientific reason to dispute that there is [STRIKE]no[/STRIKE] matter beyond the observable Universe? Do you think that Earth is at a special, privileged position in the Universe?

    EDIT: striked out a "no", which was originally unintended. :)
     
    Last edited: Aug 24, 2013
  21. Aug 24, 2013 #20
    As far as I know, there is no consensus whatsoever on the definition of multiverse (in my opinion multiverse is a very, VERY slippery term). You can have a look at this thread which contains input from many different posters and angles.
     
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