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A Do cosmologists take spontaneous symmetry breaking seriously?

  1. Aug 13, 2016 #1
    I suppose that my questions are pretty basic, but I've been trying to find out the answers and not succeeded.

    1.- Do cosmologists really think that the vacuum state suddenly changed in the early Universe? If so, would it be like a phase transition? If so, first or second orther?

    2.- Does the vacuum energy explain anything about the Universe expansion?

    3.- Are there parts of the Universe that are not causally connected with ours? If so, did these other parts choose the same vacuum state as ours?

    After all, Higgs boson has been experimentally found and spontaneous symmetry breaking can't be be as artificial as it seems to be.

    I'm sorry for posting three questions at the same time but I don't really undestand if the Standard Model of particle physics plays any relevant role in Cosmology or not. If this is not the right place to make this questions could you, please, let me know where can I look for answers?
     
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  3. Aug 13, 2016 #2

    Simon Bridge

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    1. The concept of spontaneous symmetry breaking is taken seriously - the detaiils are pretty much up for grabs. The usual analogy is to a narrow cone balanced on it's point. Any small change in the mass distribution of the cone will cause it to fall over - it's orientation state moves from unstable to one of many possible stable (lying down) states. Spontaneous state changes are well observed in Nature, ie with nuclear decay and arises from the mathematics of quantum mechanics.
    Some state changes or symmetry breaking is considered to be analogous to a state change in matter and the "order" that this is treated at depends on the model being constructed.

    2. Vacuum energy (afaict) is usually considered to have a small if not negligible effect on the cosmological expansion. If there is any effect, it is expected to increase expansion. It's tricky since the precise nature of vacuum energy remains under investigation. (Also see "Hawking radiation" for another effect that could have cosmological implications.)
    Since there are big unknowns here, you will find a lot of speculation online that boils down to an argument from ignorance: tread carefully.

    3. If I understand you correctly... It appears that there must be parts of the Universe not causally connected to ours since best evidence to date suggests an infinite flat universe. That would be any part of the Universe beyond the cosmological horizon iirc. However, since physics needs to be continuous across that horizon (it's just an artifact of where we are as observers) then it seems reasonable that anyone at or near our horizon will not see anything different from what we do. Space-time there will be subject to the same boundary conditions and so you get the same energies via the same mathematics. It's kinda like this: when I stand on a high place by the shore, looking out over the Pacific, there is a limit to how far I can see: this is the horizon. It seems reasonable to suppose, without going there myself, that a ship approaching this horizon will not experience any change in sea level when they cross it and, if they do, it will not be anything to do with my horizon.
     
  4. Aug 13, 2016 #3

    PeterDonis

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    Yes. The basic mechanism is described briefly on the Wikipedia page:

    https://en.wikipedia.org/wiki/Spontaneous_symmetry_breaking

    AFAIK there is no latent heat associated with spontaneous symmetry breaking, so it would be more like a second order phase transition. However, I don't know that a specific order is given to this transition.
     
  5. Aug 14, 2016 #4
    I don't really know what to think about all this. I guess I lack background knowledge but, if SSB were to be described by a second order phase transition, shouldn't it belong to one of the universality classes? Shouldn't we then have a detailed description of what really happened? I'm probably talking nonsense. If I am, I apologize in advance.
     
  6. Aug 14, 2016 #5

    Chronos

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    As already noted symmetry breaking is demanded by modern cosmology. For a basic discussion see http://abyss.uoregon.edu/~js/ast123/lectures/lec18.html. Assuming the universe is spatially infinite, as suspected, there are regions of the universe that are causally disconnected from our observable universe. Yet, curiously enough, these regions may have been in causal contact with our universe prior to inflation. Vacuum energy in the modern, observable universe is either zero or incredibly close to zero [this is the favored point of view]. Under inflation, however, it should have been very large initially before undergoing a phase change at the end of inflation and relaxing to its current negligible value. Sean Carroll offers some discusion on this here https://www.preposterousuniverse.com/encyc.
     
  7. Aug 14, 2016 #6
    I think we're not all speaking about the same thing here. There seems to be some kind of language (jargon) barrier here. When I refer to spontaneous symmetry breaking I'm talking about the electroweak symmetry breaking, the only one that has a precise theoretical formulation and phenomenological proof in the Standard Model of particle physics. I was wondering if this SSB could be regarded as a second order phase transition because, if this were indeed the case, I'm inclined to think that this phase transition should belong to one of the universal classes and, therefore, quantitative predictions could, in principle, be made.
     
  8. Aug 14, 2016 #7

    PeterDonis

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    Electroweak symmetry breaking has features in common with a phase transition (the term "electroweak phase transition" is sometimes used to describe it), but I don't know that the entire mathematical theory of it is exactly the same.

    What sorts of quantitative predictions are you thinking of?
     
  9. Aug 14, 2016 #8
    As far as I know there's no mathematical proof, but it is widely believed that all 2nd order phase transitions do belong to one of the so called "universal classes". Universal classes depend only on very general properties of the Lagrangian density, such as number of dimensions and symmetries. Since the low energy (T=2.7 K) vacuum energy state is known, as well as the physical quantum fields (Standard Model of particle physics), I kind of expected that physicists had already figured out the university class electroweak SSB (or "EW phase transition") belonged to. I also kind of expected the high temperature (T>10^15 K) quantum fields (before EW-SSB) and the vacuum state to be known and its cosmological consequences also to be widely known.

    Most probably I haven't been able to find that information because I'm an ignorant and my reasoning is completely flawed.
     
  10. Aug 14, 2016 #9

    Chronos

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    The general consensus is electroweak symmetry breaking is a first order phase transition. See https://arxiv.org/abs/1401.1827, Higgs Couplings and Electroweak Phase Transition, and https://arxiv.org/abs/1604.04526, A First-Order Electroweak Phase Transition in the Standard Model from Varying Yukawas for discussion.
     
    Last edited by a moderator: Aug 14, 2016
  11. Aug 14, 2016 #10

    Chalnoth

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    I think the problem is that there are multiple possible high-energy configurations which may potentially have resulted in the current vacuum state. In short, we don't know the Langrangian that was active at the time of the symmetry breaking, which makes it rather difficult to make many statements.

    To put a lot of this in more concrete terms, the nature of the spontaneous symmetry breaking events that happened in the distant past of our universe depends critically upon physics at higher energies than the standard model of particle physics currently describes.
     
  12. Aug 14, 2016 #11
    I would have expected that the physics described by the Standard Model above EW unification energies to be well known. I'm aware that there's no hope of any direct experimental confirmation, but I thought that, even though the energy extrapolation is really wild, it was a model that cosmologists could work with. It seems clear to me now that it's not. Sorry for wasting your time and thanks for your posts!
     
  13. Aug 14, 2016 #12

    PeterDonis

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    I don't think these papers describe a "general consensus". I think they describe possible models for a first order transition, but those models require physics beyond the SM which has not (yet) been observed experimentally.

    The first paper explicitly says, on p. 2:

    So any model including a first-order transition would have to go beyond the SM.
     
  14. Aug 15, 2016 #13

    Garth

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    Cosmologists certainly do take spontaneous symmetry breaking in the very early universe seriously and the concept of it being 'spontaneous' (in other words stochastic - 'by chance') is contingent on there being an infinite ensemble of other possible outcomes that inevitably lead to the concept of a multiverse.

    The analogous example of a pencil standing on its point and then tipping over in one particular direction implies that it is free to fall in any other direction, and in our analogy these other directions represent the other universes with different physical properties that would arise out of the process.

    There is a caveat here though.

    Unless we have explicit proof that these other universes exist the concept of the multiverse has dubious value within science. For it to be something more than a speculative hypothesis we have to show that the symmetry breaking is truly spontaneous and not an example of an explicit symmetry breaking process. If it were the latter then there would be some physical process that made the universe turn out the way it has.

    The problem with the hypothesis of spontaneous symmetry breaking in the very early universe, and its associated multiverse, is that we can explain everything and anything by it: anthropic coincidences, the physical nature of the observed universe etc. They have turned out this way in our universe, by chance, but It is otherwise in other universes.

    The problem with this is that a hypothesis that explains everything and anything actually explains nothing and moreover short circuits the scientific inquiry that might have found the real reason for things being as they are.

    Just a thought.....
    Garth
     
    Last edited: Aug 15, 2016
  15. Aug 15, 2016 #14
    SSB has a very precise and different meaning in particle physics: it's the way in which the intermediate vector bosons (and, by extension, many of the rest of elementary particles) became massive. It's a well defined and experimentally proven hypothesis (Higgs boson and, therefore, Higgs field, do seem to really exist).

    I'm not a physicists, just an engineer, but it really frightens me to see that high energy physicists and cosmologists can't understand each other. I'm not criticising it (the same thing happens in my own field), I'm just acknowledging a fact.

    I sometimes think that specialization and the "publish or perish" paradigms are killing Science.
     
    Last edited: Aug 15, 2016
  16. Aug 15, 2016 #15

    George Jones

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    What led you to make these uncharitable, unfair, and untrue statements.
     
  17. Aug 15, 2016 #16

    Chalnoth

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    Argument from consequences. Just because spontaneous symmetry breaking implies things about the universe you don't like doesn't mean it isn't likely.

    Explicit symmetry breaking processes are generically more complex than spontaneous symmetry breaking processes (as you need not only a mechanism to break a symmetry, but also a mechanism to break it in a specific way), and are therefore less likely.

    More importantly, there were probably a large number of symmetry breaking events in the past of our universe, and it's highly unlikely that they all would be explicit.
     
  18. Aug 15, 2016 #17

    Garth

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    Obviously spontaneous symmetry breaking events take place, it's just when they are invoked in speculative theory about the very early universe to "predict" the existence of a multiverse that I have reservations.

    Its not that I don't like the implication of a multiverse, it's just that I think its not very scientific.

    We need to be transparent about when theory is founded on testable hypotheses and when it is simply building speculation upon speculation, as discussed by George Ellis in this article in 'Nature' Cosmology: The untestable multiverse.

    Garth
     
    Last edited: Aug 16, 2016
  19. Aug 15, 2016 #18

    Chalnoth

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    Except what you wrote is that explicit symmetry breaking is the preferred default hypothesis because it doesn't lead to a multiverse.
     
  20. Aug 16, 2016 #19

    Garth

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    Not because it doesn't lead to a multiverse but because the symmetry breaking process might have been explicit.

    We haven't observed any of the other universes of the multiverse.

    Therefore, if we explain features of the early universe simply by chance, by the stochastic process of spontaneous symmetry breaking, thereby requiring the ensemble of other non-observed possibilities, we may be missing the real physical reason why the universe has turned out the way it has.

    I've no objection to doing this as long as we are transparent about the enormous implicit assumption (a multiverse) that has been surreptitiously adopted and the consequential short-circuiting of the scientific method.

    Garth
     
    Last edited: Aug 16, 2016
  21. Aug 16, 2016 #20

    Chronos

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    An idea devoid of observational evidence lacks any tangible scientific basis.
     
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