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Featured I Is the multiverse fake physics?

  1. Jan 25, 2017 #1
    woit over at his blog not even wrong considers string theory based multiverse to be fake physics. he cites sean carroll as others on his blog as examples of fake physics.

    is string theory based multiverse fake physics?
     
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  3. Jan 25, 2017 #2

    Orodruin

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    It is customary to include a link when discussing blog posts or similar.
    http://www.math.columbia.edu/~woit/wordpress/
    Not everyone reading will know the blog.

    I think he has a clear point. Large parts of theoretical physics has become untestable and therefore unscientific. Trying to sell this as facts or success is misleading.
     
  4. Jan 28, 2017 #3

    ohwilleke

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    I agree that the multiverse (not to be confused with the many worlds interpretation of QM) is fake physics.
     
  5. Jan 28, 2017 #4

    Orodruin

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    To be honest, I would still place QM interpretations into the same category. It is also a subject that is given far too much attention in popular discussion on QM.
     
  6. Jan 29, 2017 #5

    haushofer

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    Can you elaborate?
     
  7. Jan 29, 2017 #6
    ohwilleke is replying to my thread which is itself based on the claims of peter woit on not even wrong that
    the multiverse is fake physics in analogy to fake news. even when claims of multiverse comes from
    a cosmologist and phd like sean carroll or brian greene it is still fake physics.

    woit says claims of the multiverse is based on string theory unification, which he regards to be a failed
    research program, therefore physicists like sean carroll and several others he mentions are not discussing
    genuine physics to a lay public.

    what do the resident string theorists here say to this claim, i.e urs shcrieber et al
     
  8. Jan 30, 2017 #7

    haushofer

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    Well, I've read a fair amount of string theory and my own research involved it, so let me give my 2 cents.

    The motivation for the multiverse from string theory is shaky. It involves an interpretation of the landscape, which is on its own quite ad hoc. I think the motivation from inflation is stronger: to get the right amount of inflation results quite naturally in eternal inflation. Let's say that at some time in the future we are very confident that inflation happened, and that our model implies eternal inflation. Philosophically, we entered then a boundary of our understanding: we have no way to falsify the implied multiverse, but as a consequence of our model we should take it seriously. There is nothing fake about that. It would be fake to reject it because we don't like the idea that we bumped into an end of our understanding. Physics thaught us that we should take our equations seriously. If we are just one bubble in a multiverse and we cannot enter those other bubbles, then that's the way reality is; nature doesn't care about being falsifiable.

    But often people combine this 'inflationary multiverse' with the 'string landscape multiverse'. I don't see how that happens, and it is far from clear what the relation (if any) is. Let alone the multiverse from the MWI-interpretation. It is only in those cases you enter these "theory of anything"-objections agains the multiverse.

    To be honest, if I had to choose, I would say that the MWI-interpretation of the multiverse is much more shaky than the inflationary multiverse. I've never understood why people like MWI, but that could also be my lack of deep knowledge of it.
     
  9. Jan 30, 2017 #8

    haushofer

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    It depends on how you view science and physics. I strongly disagree with your view. Ontology, and as such interpretational issues, should imo be considered as a part of physics, and not 'just' philosophy.
     
  10. Jan 30, 2017 #9

    Orodruin

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    As you have guessed, I strongly disagree with this. If there are no testable differences, I see no scientific point in debating the issue. Just pick whichever interpretation you fancy (if you must) and nobody can disagree with you. To me this violates the very core of empirical science.
     
  11. Jan 30, 2017 #10

    ShayanJ

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    What if in 10 years, people still have no explanation for fine tuning? In 50 years? In 100? Even then you don't think we should consider the multiverse?
     
  12. Jan 30, 2017 #11

    Orodruin

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    No. It is a concept similar to God (I am using God to cover three of the main world religions - anyone may substitute for personal preference). I give you the two hypotheses:
    1. Fine tuning exists because of the multiverse.
    2. Fine tuning exists because God wanted it so.
    I ask you the question: What testable differences exist between those two hypotheses?
    If neither hypothesis can be falsified, I simply chose the agnostic path and do not include any of the hypotheses in my scientific description of how the world works. (I also have the same approach to religion by the way, but that is a different matter.)
     
  13. Jan 30, 2017 #12

    ShayanJ

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    The difference is that eternal inflation may be a good theory with strong observational support. We may find out that we can't come up with a better theory. Why should we throw out a prediction of our only good theory?
    Its like gravitational waves, people didn't doubt their existence. No one actually was surprised when they were discovered because GR is a very well established theory.
     
  14. Jan 30, 2017 #13

    Orodruin

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    Please show me this observational support.

    What do you mean "better"? If two theories makes the exact same predictions apart from things that cannot be tested - they are the same theory for all practical purposes and you can never find out which is preferred. Predictions that cannot be tested are not predictions because predictions by definition makes statements about things that will occur or not.

    This is different. Gravitational waves were a priori testable and based on the current dominating theory - which had already made a large amount of verified predictions that differed from its predecessor (Newtonian gravity) - they should be there. So I ask you, what predictions of the multiverse have been observed that cannot be explained without it?
     
  15. Jan 30, 2017 #14

    ShayanJ

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    I said maybe. I meant in the future, it may turn out to be so!
    In the future, hypothetically, just imagine, that eternal inflation explains all observations really well and any other theory that doesn't predict a multiverse, is much more complicated. Imagine its like the choice between SR and aether theories. So people choose eternal inflation. They have observed all its predictions except for the multiverse. Why should they assume its not true?
     
  16. Jan 30, 2017 #15

    Orodruin

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    But this is the other way around! You can do away with the aether in LET and just be left with SR because there is no need to assume the aether of LET. In the same way, there is no need to assume an eternal inflation to explain what is going on in the observable universe.

    Of course you can try to extrapolate a theory, but doing so you must be aware of that this is what you are doing - just as we know that we are extrapolating GR to a domain that by definition of the theory itself is untestable when we try to describe the interior of a black hole. If the theory is true in that regime - then you can never know that it is.
     
  17. Jan 30, 2017 #16
    where does string theory and its prediction belong on this list?
     
  18. Jan 30, 2017 #17

    FactChecker

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    Are you saying that something must be testable in order to be true? Or is your objection more about calling it physics?
    What about a modern theory that is compatible with all we know today? Doesn't that imply that it passes the "test" of all our current knowledge?
     
  19. Jan 31, 2017 #18

    haushofer

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    A physical theory must do more than just 'agree with observation' in view of future development. An example is given by the epicykle theory, which reproduces observations concerning our solar system perfectly in a geocentric model. Mathematically we now understand why: given any irregular shaped closed curve, we can always use a finite number of epicykels to explain such a curve.

    That's why I don't understand how some people can just put ontology into the 'philosophy'-corner and pretend it is not part of physics. It is. E.g., one reason why quantum gravity is not well understood could be in a similar fashion as the epicykels: we can calculate with it, but by regarding QM just as a bookkeeping device, we could overlook crucial hints which are important when considering gravity.

    Similary, nowaydays the discussion about the nature of spacetime and the meaning of coordinates can be regarded as 'mere philosophy', but it troubled Einstein so much that for two years he abandoned general covariance. And I think that general covariance is still not thoroughly understood, by the community and also by a lot of professional physicists.
     
  20. Jan 31, 2017 #19

    Orodruin

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    Yes, it must do so without introducing additional arbitrary epicycles that can fit any observation. Furthermore, epicycles would have lost out to Occam's razor long ago.

    Introducing different equivalent interpretations is not going to help you achieve this. Thinking about different and a priori distinguishable theories just might.
     
  21. Jan 31, 2017 #20
    There are good reasons to be concerned about the unitary-only MWI approach. If one looks deeply into the foundations of MWI, one finds circularity and arguably worse logical fallacies. See, e.g, https://arxiv.org/abs/1406.4126 and https://arxiv.org/abs/1603.04845
     
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