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Does gravity break down in the big bang?

  1. May 18, 2013 #1
    Dear all,

    I just read something in a book by Lawrence Krauss which I don't understand. I hope you can answer my question:

    Kraus makes the argument that if you take quantum mechanics and gravity, something is more energetically favorable than nothing. Hence if you take nothing, at some point something will arise.

    My question is:

    Doesn't gravity (or maybe quantum mechanics, too) break down, like the nuclear forces, in the big bang?

    If so, then does Kraus's argument still hold? Or do I interpret it wrongly?

    I'm a biologist and only read bits a pieces about physics, so forgive me if I've said something ignorant, which I know is easy to do.

    Kind regards,
    Daan from Amsterdam
     
  2. jcsd
  3. May 18, 2013 #2
    I haven't read Krauss' book and so can't comment on the larger argument and whether or not it holds.

    As for your particular question, though, it's important to distinguish between "X breaks down" and "our understanding of X breaks down". Our mathematical models for gravity (and other forces) break down at the Big Bang (which is the reason physicists borrowed the word "singularity" from the mathematicians for such situations). That doesn't necessarily mean the forces themselves break down at the Big Bang, just our current understanding of them. The break down of our mathematical models in such circumstances is precisely why physicists are currently looking for better ones.
     
  4. May 18, 2013 #3

    phinds

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    daanaerts, one of the things you should keep in mind is that pop science discussions sometimes fail to distinguish between the two meanings of the term "big bang". There really is a big bang EVENT and a big bang MODEL. The event is what is also called the singularity and since our math models break down there, we don't know WHAT that was all about. The model is also called the "Big Bang Theory" and has nothing to do with the singularity but only discusses what happened about one Plank time AFTER the singularity and from there forward.

    I think Krauss's discussion is an attempt to discuss the singularity as an evolution out of "nothing", whatever that is, via quantum foam --- A Universe from Nothing is the title of one of his books.
     
  5. May 19, 2013 #4
    Alright, thanks for your responses.

    But then my problem is that, in my mind, nothing (which I can't and never will be able to imagine) doesn't have dimensions, forces, anything whatsoever.

    So in any case, he postulates to get something from nothing, you need gravity. But isn't an empty space with gravity not nothing? Because that already has three spatial dimensions and gravity.
     
  6. May 19, 2013 #5

    phinds

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    Uh ... why?
     
  7. May 19, 2013 #6
    edit: ' he postulates to get something from nothing, you need gravity.' he probably means a dynamic geometry...a changing spacetime....see below....



    'You'll have to define what you mean by 'nothing'....Is it different from 'empty', or the 'vacuum'....for example .....those descriptions were once thought to apply to space but quantum mechanics suggests a different understanding is required. And another view of that is via gravitational and electromagnetic fields, for example, which seem to permeate everything everywhere. But there is more:

    As if this were not crazy enough, such vacuum energy contains, some say is caused by, virtual particles...particles we can't detect as such but which manifest as forces....And this leads to some aspects of the big bang: vacuum energy can spawn REAL [locally detectable] particles. Cosmological inflation, which shortly followed the big bang, was apparently part of a phase transition from a high vacuum energy unstable state to the separate forces, time, matter and energies we observe today as separate entities. In other words, dynamic spacetime, or dynamic geometry if you wish, together with the vacuum energy of the early universe produced most of what we observe around us today.


    Well, what 'broke down' was a single high energy symmetric entity for which we don't have a complete theory. It's a 'grand unification' entity of some sort. This state was unstable and resulted in 'spontaneous symmetry breaking'..... that's the phase transition I just mentioned. So time, energy, some of the fundamental elements, electromagnetic [light] energy, time, gravity, all emerged from that symmetry breaking. And something from that still powers the expansion of the universe right now....some call it the cosmological constant, some dark energy. It's part of the 'nothingness' of space...really, of spacetime.

    I know that on some level it makes little sense, but just wait another 100 years and see what happens!!
     
  8. May 20, 2013 #7
    anything breaks beyond big bang, quantum mechanics, relativity mechanics, read in this forum FIREWALLS.
     
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