1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I T-symmetry and WDWE with regards to a Universe from Nothing

  1. Sep 8, 2017 #1
    The article Spontaneous creation of the universe from nothing (Dongshan He, Dongfeng Gao, and Qing-yu Cai) published by the American Physical Society discusses a mathematically proof that the universe could be spontaneously created from nothing using the Wheeler-DeWitt equation (pictured below).

    It seems that, despite the proof Dongshan, et al provide, their argument requires the universe to start with many physical laws and quantum properties built in which seems to negate a true conception of absolute nothingness.

    However, given the premise of the universe starting as nothing, couldn't T-symmetry and simple mathematical properties explain this?

    Given the equation 0=0, you can theoretically perform an infinite number of calculations as long as you did them for both sides or included the reversal of those equations. You could start with 0 and add every quantum state and physical interaction over the history and future of the universe and as long as you also perform the reverse of those states, i.e. T-symmetry.

    Am I missing something here?

    [​IMG]
    upload_2017-9-8_11-56-12.jpeg
     
  2. jcsd
  3. Sep 12, 2017 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    That is correct... the authors are not proposing a Universe from absolutely nothing. After all, there must be the possibility of a Universe forming, and that is not "absolutely nothing".

    It is not even clear what "absolute nothing" means in this context, or how we could demonstrate that such a state could exist, since most attempts to define it are incompatible with the definition of "exist". So it is unclear what you mean by "true" in this context.

    Just in the abstract:
    "[the authors] show that, once a small true vacuum bubble is created by quantum fluctuations of the metastable false vacuum..."
    ... so did you find what they were calling a "true vacuum"?
    ... did you look at the papers that cited this one?

    What they are proposing, loosely, is that if the phase space of possible Universes is linked in a particular way, then the state of "no universe" would be unstable. It amounts to, "if this maths is correct, then a Universe must exist... and this Universe is among the set of Universes that could exist."

    The point is to test the maths rather than to prove that a Universe could come from a particular definition of "nothing".
    The model is good if it leads to what we observe.
    That is what Science does.
     
  4. Sep 17, 2017 #3
    The idea a universe can come from nothing, is closely related to the quantum tunnelling model of the universe by Vilenkin. Hawking proposed further with Hartle the no-boundary wave function and applied similar ''something from nothing,'' concepts. Let's be clear, Hawking's model was nice, but there is a growing opinion among scientists that it is fundamentally incorrect. To get some idea of those thoughts, you can read the following:

    http://www.dailygalaxy.com/my_weblo...d-another-picture-of-the-infant-universe.html

    The Wheeler de Witt equation has its own problems... and in fact, many scientists argue it also is problematic and most likely wrong. Among some of the less technical problems, one of them has been widely known as the time problem. Why does the time derivative vanish for a universe and is this the right picture? Further, without time dependence, what does that do to the quantum models we have which depend on time evolution?

    Certainly, I feel, we have some time to go.
     
  5. Sep 17, 2017 #4

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Aside:
    I ran into a description of "universe from absolutely nothing" which pointed out that a state of "absolute nothingness" has to be intrinsically unstable since to be absolute it must have no rules. (If there are rules like, "nothing can come from this nothing" then it is not absolute nothing.

    I'm not keen on this sort of semantical argument ... but it does highlight a common flaw in how most people seem to be thinking about it.

    The issues surrounding the models (see post #3) look, to me anyway, like that ... but at least there is a kind of narrowing down of what we mean when we talk about a beginning for the Universe, and what we mean by "nothing".

    I agree that there's a ways to go yet.
     
  6. Sep 17, 2017 #5
    I think most rational thinkers, including myself, would admit it makes no sense to talk about something from nothing - it may become more popular to think of the thing that gave rise to a universe, is in fact a configuration of everything that could be possible.

    This could be thought of in terms of a wave function to a universe. Certainly, the wave function would have to dictate how a universe comes into existence. A wave function to a universe does give an elegant picture, it says before a universe came into existence, it had an infinite amount of start up conditions it could have chosen from. The ultimate question is how this single reality was chosen out the infinite smear that had to pre-exist a collapse state?
     
  7. Sep 17, 2017 #6
    One answer is all states actually exist in a multiverse, or ''megaverse'' as Susskind calls it. But for again, rational reasons, not many of us believe in it. Plus, it doesn't retain Popper falsifiability, which is one reason physicists are arguing against inflation now, because it leads to an eternal inflation of many universes. Paul Steinhardt, one of its creators, is now a vocal opponent against.
     
  8. Sep 17, 2017 #7

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Yep... and we are not too far into philosophy and not enough physics.
    Also wandering off topic I suspect... we should hear back from OP before continuing.

    I just didn't think there was any point addressing the stated question before settling suspected misunderstandings in the background assumptions.
    The question itself could just turn out to be a conceptual maths issue.
     
  9. Sep 17, 2017 #8
    His question seems to be, can we create a negative time, extending before the big bang? I'll answer his question directly, sorry... the answer is no. In relativity, and in the standard model, the big bang was the creation of space and time itself. It makes no sense to talk about time symmetry before it.

    Nevertheless, don't take this as the absolute model - there are models which are attempting to ask the question about what happened before the big bang. In those cases, the big bang was not the beginning of time per se.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: T-symmetry and WDWE with regards to a Universe from Nothing
Loading...