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Which stable 'multiverses'?

  1. Apr 14, 2012 #1
    We always get to know that there could be other 'multiverses' with completely different physical constants, but I'm wondering in particular if it is possible to re-adjust the natural constants in order to obtain stable atoms? That should not be too difficult to estimate, isn't it? Did someone speculated more precisely on this by making appropriate calculations?
     
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  3. Apr 14, 2012 #2
    What do you mean 'obtain stable atoms'? We have stable atoms in this universe or else we wouldn't be here.

    On a larger note though, the multiverse theory is a not-widely-accepted theory with little mathematical (if any) backing. If you theorize that these other universes could have different physical laws/constants, then there is no limit to what you can say would be changed.
     
  4. Apr 15, 2012 #3
    What I'm looking for is some calculation made about the effect it could have on our physical world if say Planck's constant, or the speed of light, the electron charge and mass, etc., were slightly different? For example, how would the atomic spectra or the size of atoms change by changing slightly these constants? It is not just about multiverses, it is about understanding how and to what degree nature's constants determine the world we observe. Nobody did some work on this beyond generic multiverse ruminations?
     
  5. Apr 15, 2012 #4

    mfb

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    That depends on the (possible) connections between these constants and maybe some deeper theory of our universe. But of course you can consider the effects of changes of these forces at the nuclear energy scale. I don't know of any reference, and exploring the atoms in our universes probably has enough open problems ;).

    You could get other stable nuclei with other fundamental constants, and the electron energy levels depend mainly on the electron mass and the fine-structure constant.
     
  6. Apr 15, 2012 #5

    Chalnoth

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    This is generally false.

    The reality is that "multiverse" captures a diverse array of ideas within physics. That we live in some form of multiverse is a general expectation of our currently-accepted theories (e.g. the standard model of particle physics), and becomes even more likely in basically all of the decent candidate theories that we are exploring.

    However, we cannot at this time say much of anything about the precise nature of the multiverse. That there is a multiverse of some kind is highly certain. Its specific nature is not.

    That's not at all true. Just because some things can change doesn't mean everything can. For one, the laws of physics that result, no matter what they are, must be self-consistent. That requirement is surprisingly restrictive.
     
  7. Apr 15, 2012 #6
    I agree with that, I guess I should have said what I said differently.

    Really? What makes the existence of a multiverse so certain?
     
  8. Apr 15, 2012 #7

    Chalnoth

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    The main thing to point out here is that there are a great many ways of arriving at the same conclusion. That is why I am so sure.

    But a really really short argument is to point out that spontaneous symmetry breaking is a fundamental aspect of the standard model of particle physics, and is even more important in grand unified theories. And the existence of spontaneous symmetry breaking basically guarantees the existence of other regions of space-time with different low-energy physics (regions where the spontaneous symmetry breaking events happened differently).

    We don't yet know just how important these spontaneous symmetry breaking events were, so we don't know precisely what aspects of physical law are different in different regions of space-time. But that low-energy physics differs by at least some amount seems highly certain.
     
  9. Apr 15, 2012 #8
    I now realize that I shouldn't have used the multiverse analogy and use a different title. Because the question I'm making here is independent from the existence or not of multiverses. It is about the role of the possible **combination** of the physical constants. For example in Bohr's atomic model if one maintains the ratio of the squared Planck's constant over the electron mass we obtain the same atom size and energy levels. So, could be there a set of values in the constants that would render OUR universe 'invariant'? Of course Bohr's model is an outdated one but just for this reason I was wondering if someone worked along these lines with more precise and modern physics calculations?
     
  10. Apr 15, 2012 #9
    Either you think our universe is 'one of a kind' a 'never to be repeated anomaly' or you think it's likely stuff like that goes on all the 'time'; what we know of quantum mechanics clearly suggests the latter.

    In any case, while the 'constants' [using that term really loosely] in our universe do appear finely tuned, and the range of values IS restrictive as noted already, seems like you could get an infinite number of variations in the 66th decimal place and beyond, for example, and that such a universe would be 'viable'.....

    Relating directly to your question, check out this short section:

    http://en.wikipedia.org/wiki/Multiverse#Level_II:_Universes_with_different_physical_constants
     
  11. Apr 15, 2012 #10

    Chalnoth

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    Unfortunately, we don't really know how much the fundamental constants might be able to change, or how changes in one constant might affect the others.

    Oh, you certainly can come up with changes to the fundamental constants that leave it so that no measurements change. But if that is so, then have you actually made a change at all, or just reshuffled your numbers around?
     
  12. Apr 15, 2012 #11
    Ok, I know that I have still quite confused ideas on the subject, but that's why I asked here... I found this on the web from John Barrow, in "The Constants of Nature" (2002). This was the point that came to my mind and could not believe that nobody worked on this further.... I'm looking for an in depth analysis.

    "[An] important lesson we learn from the way that pure numbers like α define the world is what it really means for worlds to be different. The pure number we call the fine structure constant and denote by α is a combination of the electron charge, e, the speed of light, c, and Planck's constant, h. At first we might be tempted to think that a world in which the speed of light was slower would be a different world. But this would be a mistake. If c, h, and e were all changed so that the values they have in metric (or any other) units were different when we looked them up in our tables of physical constants, but the value of α remained the same, this new world would be observationally indistinguishable from our world. The only thing that counts in the definition of worlds are the values of the dimensionless constants of Nature. If all masses were doubled in value [including the Planck mass mP] you cannot tell because all the pure numbers defined by the ratios of any pair of masses are unchanged."
     
  13. Apr 15, 2012 #12
    Aiydan, this is an interesting point, but applies only for dimensionless parameters. Changes in empirical physical constants, however, would result in dramatic changes in the universe. For example, if we altered the value of the gravitational constant, we would have a significantly stronger gravitational force.
     
  14. Apr 15, 2012 #13

    mfb

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    Or we would have heavier particles.
    Unless the ratio of particle masses to the planck mass follows from some deeper, unknown theory, in that case it might by fixed.

    Particle masses relative to the planck mass, the interaction strength of strong and electroweak force, the higgs mechanism parameters, the CKM quark mixing parameters, the PMNS neutrino mixing parameters and maybe something I forgot. These are the dimensionless constants which you can change in the standard model. Maybe a "theory of everything" can even fix some of these.
     
  15. Apr 16, 2012 #14
    It seems that things are not easy as that. I found that this has already been discussed on PF: https://www.physicsforums.com/showthread.php?t=226736

    I strongly suggest to read wiki on Planck units (especially the chapter "Planck units and the invariant scaling of nature"): http://en.wikipedia.org/wiki/Planck_units

    But things seem to be also quite controversial. For example see:

    http://xxx.lanl.gov/abs/physics/0110060

    and

    http://arxiv.org/abs/hep-th/0208093

    I'm trying to go through this and have still to grasp things.... not sure to understand. But, as far as I could find on the web, it seems that this controversy has not been settled until nowadays, or did it? Would be interesting to find some update.
     
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