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Is my reasoning correct? Energy "before" the big bang?

  1. Jan 30, 2015 #1
    It seems as though that according to conservation of energy, there could never have been a point in the timeline of the universe where nothingness existed. It seems to me that the claim that there was nothingness before the big bang would violate these laws. For example if E is the total energy of the universe then the law states that E = constant. If E1 is the total energy of the universe at an arbitrary time t1 and E2 is the total energy of the universe at arbitrary time t2 , then E1 = E2. lets say t1 is before the big bang and t2 is right now. If there was nothingness before the big bang, then E1 = 0. Since right now it is obvious that E2 > 0 , or , E2 != 0, then E1 != E2 which would violate conservation of energy. Is this line of reasoning correct? if not, why?
     
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  3. Jan 30, 2015 #2

    mfb

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    Without a universe, there is no conservation law a big bang could violate. "Before the big bang" is meaningless if the universe started with it, and you cannot assign an energy to something that does not exist.

    By the way: general relativity does not have global energy conservation.
     
  4. Jan 30, 2015 #3

    jfizzix

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    Conservation of energy arises due to the time translation symmetry of the laws of physics (see Noether's theorem).

    Our current theories say that there is effectively no time before the Big Bang (in the geometric sense that one cannot go further north than the North Pole). If that's true, then one simply cannot translate from the Big Bang further into the past and say the laws of physics remain invariant.

    If there is no time translation symmetry at the point of the Big Bang, there is likely no conservation of energy (as we know it) either.

    At least currently, we can only speculate about what the laws of physics were like before the big bang (if there even was a "before").
     
  5. Jan 30, 2015 #4

    jfizzix

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    Is that not what "dark energy" and the "cosmological constant" is for?

    Time translation symmetry is certainly a tricky thing in general relativity, but is there really no workaround?
     
  6. Jan 30, 2015 #5

    mfb

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    No. There is no unique meaningful way to define "the energy of the universe at a specific point in time", and as far as I know no matter how you define it there is a process that could change it.
     
  7. Jan 30, 2015 #6
    Why do you think it's obvious? It is not.
    There is a possibility that E2=0. See Lawrence Krauss' book "A Universe from nothing", for example.
     
  8. Jan 30, 2015 #7
    How do we know that the big bang is the origin of time and not just an event that happened in time? Is there a mathematical/scientific reason or is it an axiom we have adopted?

    If total universal energy is not conserved in GR , is it still conserved in isolated systems? Is it also true that universal E conservation does not apply to SR?

    As for the current total E being 0... How is this possible? Wouldn't that mean nothing can happen?
     
  9. Jan 30, 2015 #8

    phinds

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    We don't know, we just have a model that represents reality incredibly well and as has already been stated, it is unable to handle what happened at or before the big bang singularity (aka t=0) or if there even IS a "before".

    Just today I made a post claiming that energy is conserved in closed systems and was told that that is wrong. See here:

    https://www.physicsforums.com/threads/universe-already-existed.795055/#post-4993340
     
  10. Jan 30, 2015 #9
  11. Jan 30, 2015 #10
    Ok thanks i have some stuff to read now. Btw sorry i didnt realize such a similar question had been posted. In fact i just realized how often you guys probably get this exact question. Sorry :( in school i am still studying classical physics so i have so far only been taught that total E is always conserved and have even done several experiments myself that demonstrated this, so the idea that the energy laws do not always hold is new to me
     
  12. Jan 31, 2015 #11

    mfb

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    Energy is conserved in special relativity, and there is still local energy conservation in general relativity (which means your lab experiment won't find a deviation).
     
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