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Multiverse Evidence Explanation?

  1. Jun 14, 2013 #1

    TheDemx27

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    My friend keeps on harping on this sort of stuff. He says that there is a gravitational pull from other universes affecting the matter in this universe and creating imperfections in the cosmic background radiation. I find it hard to believe that any sort of boson would be able cross the nonexistent space between universes. Someone please explain.

    Thanks.
     
  2. jcsd
  3. Jun 14, 2013 #2

    mfb

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    As far as I know, there is no sign of such an influence. Just ask him for a reference ;).

    The temperature fluctuations can be explained with our own universe only - in fact, they fit very nicely to the model predictions.
     
  4. Jun 14, 2013 #3

    phinds

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    Tell him he's been watching too much TV "science".
     
  5. Jun 14, 2013 #4

    Chronos

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    A recent claim of evidence for a multiverse was promoted by Kashlinsky in: A new measurement of the bulk flow of X-ray luminous clusters of galaxies, http://arxiv.org/abs/0910.4958. It has been frequently criticized by the mainstream, largely because it does not demand the existence of a multiverse to be explained. A paper in 2011 is regarded as refuting Kashlinsky's assertion: Measuring the cosmological bulk flow using the peculiar velocities of supernovae, http://arxiv.org/abs/1102.0800. Planck data also casts doubt on the significance of any bulk flow in the universe: On the Statistical Significance of the Bulk Flow Measured by the PLANCK Satellite, http://arxiv.org/abs/1303.6614. To date, there is no firm observational favoring the multiverse concept. If other universes are causally disconnected from ours, as usually suggested, it is unclear how such evidence could be gathered.
     
  6. Jun 15, 2013 #5

    Garth

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    The problem is that any 'evidence' for the multiverse is likely to be able to be also explained by other less exotic causes.

    It is interesting to see how keen some are to find evidence no matter how insubstantial; compare with the discovery of the Higgs boson that was not confirmed until it had reached 5 sigma significance.

    Garth
     
  7. Jun 15, 2013 #6
    Edit: Nevermind. I didn't read the cosmic background part. I'll still leave this here, these videos were more like standup comedy.

    (What I meant: Start at 6:50)
     
    Last edited by a moderator: Sep 25, 2014
  8. Jun 15, 2013 #7
    The multiverse is not tv science. Its a serious proposal by serious cosmologists. It may well be wrong, and I'll come to that in a moment, but we should not dismiss it as as "Tv science".
    There are several different multiverse concepts. The one that I think that should be taken the most seriously is eternal inflation.
    You can read Alan Guth's case for a multiverse here:
    http://arxiv.org/abs/hep-th/0702178
    or watch his talk here:
    http://pirsa.org/index.php?p=speaker&name=Alan_Guth

    There are two questions then that the existence of the multiverse in this framework depend upon. Is there observational evidence that inflation happened and is it true that if inflation happened it is necessarily eternal or is it one time event only? If we want to know if a multiverse is real or not these are the questions we need to address.
    On the first question the evidence seems so far to suggest inflation did happen, but we would still I think like to see the evidence from gravity waves to be more sure.
    On the second question there are two possible routes. Explore Guth's maths that implies that if inflation happened once then it must happen again and again in other regions of the universe, creating a multiverse or look for evidence of bubble collisions in the CMB.
    I think its possible that inflation did not happen and even if it did, Guth has his sums wrong.Or perhaps quantum gravity will help us understood the evolution of the inflaton field better. But these are issues to explored not written off as "tv science"
    The issue of bulk flow can be read about here:
    http://en.wikipedia.org/wiki/Dark_flow
    I dont see how eternal inflation implies bulk flow but other less cited theories of the multiverse do, such as the one proposed by Laura Mersini-Houghton. Strangely seems to be making noise that its discovered by Planck even though Planck says not. I have no idea why she is saying this, it seems to be very wrong. maybe someone has seen her recent talk and can answer that.
    http://www.math.columbia.edu/~woit/wordpress/?p=5907
     
  9. Jun 15, 2013 #8

    phinds

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    Yes, I'm aware of that. They include Lawrence Krauss, who is one of my favorite modern physicists because of his outspokenness and his entertaining presentation style. I've read his "A Universe from Nothing" and was disappointed to find that at the end he concluded that the multiverse is the only reasonable solution to some cosmological issues.

    I'm also aware that I'm personally biased against the concept, BUT ... that bias is based on the total lack of any actual evidence in addition to my belief about how Occam's Razor should be applied to the concept (it's just too damned complicated!)
     
  10. Jun 15, 2013 #9

    Garth

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    How exactly would you prove it wrong?

    There may well be other universes 'out there' but leaving no evidence of their existence in our universe.

    One objection to the multiverse concept is that it is unfalsifiable.

    Just a thought....
    Garth
     
  11. Jun 15, 2013 #10

    mfb

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    "It might be wrong" and "we can show it is wrong" are not the same.

    Unrelated:
    A common statement about other universes is "if we have no way to test its existence, it is pointless to consider it at all".
    I disagree. Consider quasars, for example: some of them are so far away that they are outside our observable universe now. We have no way to test if they still exist - but it would be foolish to propose that those galaxies just vanished!
    If some theory requires that many universes exist, and if the same theory gives good predictions about our own universe, it can be a valid view that there are "probably" many universes.
     
  12. Jun 15, 2013 #11
    The inflationary multiverse can be disproved by either showing inflaltion didn't happen or showing clearly the inflaton field doesn't evolve in the manner Guth claims.
     
  13. Jun 15, 2013 #12

    Chalnoth

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    The claim of a unique universe is also unfalsifiable. It has the additional problem that it is patently absurd.
     
  14. Jun 15, 2013 #13

    TheDemx27

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    Couldn't one argue that since there is hardly any evidence for it, that it is less of a matter of physics and more of belief or religion? Just a thought.
     
  15. Jun 15, 2013 #14
    The inflationary multiverse comes from analysing the way the inflaton field evolves. That anaylsis might be wrong but i don't see how it has any similarity to religion.
    Quanutm mechanics seems absurd to a lot of people so i dont think we should rule out anyything on those grounds. We should try and find out more about the dynamics of inflation and see if the claims made by Guth and other are right or wrong.
     
  16. Jun 15, 2013 #15

    phinds

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    Interesting point of view. I hold the opposite --- the multiverse seems patently absurd to me. Since there's no evidence either way, I hold with Occam's razor and vote for one.
     
  17. Jun 15, 2013 #16
    Have you read Guth's paper that I cited above? Of course his analysis might be wrong and his assumptions might be wrong but Im not sure why "patently absurd" is appropriate here. perhaps you can enlighten us?
     
  18. Jun 15, 2013 #17

    Nugatory

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    Everybody, serious cosmologists included, has a right to consider interesting propositions that are not currently considered falsifiable. It becomes "tv science" when the pop-sci crowd notices that a serious scientist is speaking, allows the prestige of the speaker to rub off on it, and starts overhyping it with phrases such as "exciting new theory".

    When I hear someone talking about the multiverse, I presume that they've been victimized by the pop-sci crowd until shown otherwise - and this presumption is justified by a fairly straightforward application of Bayes' Theorem :smile:
    I see no reason not to apply this presumption to someone who is identified only as a friend of the OP.

    As an aside, it has happened that people have found ways of experimentally testing propositions once thought to be not falsifiable. Probably the most striking example is Bell's theorem, which pointed to experimental tests of the philosophical proposition of EPR realism.
     
    Last edited: Jun 15, 2013
  19. Jun 15, 2013 #18

    Chalnoth

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    That's an invalid use of Occam's razor. The only way in which it makes sense is to base it off of the number of assumptions required. And a multiverse requires fewer.
     
  20. Jun 15, 2013 #19

    Nugatory

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    Absurdity, like beauty and other aesthetic judgements, is in the eye of the beholder.

    So I have good news for you and bad news... The good news is that you cannot lose this argument; and the bad news is that you can't win it either.
     
  21. Jun 15, 2013 #20

    phinds

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    I'm just biased.
     
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