Violations of energy conservation in the early universe may explain dark energy

Discussion in 'Astronomy, Exobiology, & Cosmology' started by paddoboy, Jan 20, 2017.

  1. paddoboy Valued Senior Member

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    Violations of energy conservation in the early universe may explain dark energy
    January 20, 2017 by Lisa Zyga feature

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    This is the "South Pillar" region of the star-forming region called the Carina Nebula. Like cracking open a watermelon and finding its seeds, the infrared telescope "busted open" this murky cloud to reveal star embryos tucked inside finger-like pillars of thick dust. Credit: NASA
    (Phys.org)—Physicists have proposed that violations of energy conservation in the early universe, as predicted by certain modified theories of quantum mechanics and quantum gravity, may explain the cosmological constant problem, which is sometimes referred to as "the worst theoretical prediction in the history of physics."



    Read more at: https://phys.org/news/2017-01-violations-energy-early-universe-dark.html#jCp
     
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  3. paddoboy Valued Senior Member

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    https://arxiv.org/pdf/1604.04183v3.pdf

    Dark energy as the weight of violating energy conservation

    In this letter, we consider the possibility of reconciling metric theories of gravitation with violation of the conservation of energy-momentum. Under some circumstances, this can be achieved in the context of unimodular gravity, and it leads to the emergence of an effective cosmological constant in Einstein’s equation. We specifically investigate two potential sources of energy non-conservation— non-unitary modifications of quantum mechanics, and phenomenological models motivated by quantum gravity theories with spacetime discreteness at the Planck scale—and show that such locally negligible phenomena can nevertheless become relevant at the cosmological scale.
     
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  5. SimonsCat Registered Member

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    Interestingly I have come to similar conclusions, but not by the same methods.

    If you are interested in non-conservation for the energy in a universe, here is the correct non-conserving Friedmann equation:


    \(\dot{R}\ddot{R} = \frac{8 \pi R^2}{6}[ \dot{\rho}_{on} + \dot{\rho}_{off} + \dot{\rho}_g + \dot{\rho}_{EM} + \dot{\rho}_{vel} - \dot{\rho}_{\sigma} + \dot{\rho}_{vac}]\)


    (with seven density parameters)
     
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  7. paddoboy Valued Senior Member

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    I hope that such information will be of interest to some members.

    From various reputable articles I have read, the conservation of energy violation sometimes raised with regards to the BB, is not a problem.
    In my layman's fashion I do try to picture things as simplistically as possible.
    In that regard I see the impetus of the BB itself, tied to the CC or DE and the acceleration phase we now find ourselves in.
    As spacetime expanded after the BB, the gravity from a far denser universe, overcame the DE component making it expand and so a deceleration in the expansion rate was present.
    While the DE/CC component of spacetime itself, remains constant over expansion phase, the density of the universe was lessening with the expansion, and continued until today when we see the CC/DE component starting to accelerate the expansion.
    The thing is, the Universe wasn't always accelerating in its expansion rate!
    The $64 million question is though how long will it keep expanding?
     
  8. paddoboy Valued Senior Member

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    I found this which may explain further........................
    http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/
    excerpt:
    The point is pretty simple: back when you thought energy was conserved, there was a reason why you thought that, namely time-translation invariance. A fancy way of saying “the background on which particles and forces evolve, as well as the dynamical rules governing their motions, are fixed, not changing with time.” But in general relativity that’s simply no longer true. Einstein tells us that space and time are dynamical, and in particular that they can evolve with time. When the space through which particles move is changing, the total energy of those particles is not conserved.

    It’s not that all hell has broken loose; it’s just that we’re considering a more general context than was necessary under Newtonian rules. There is still a single important equation, which is indeed often called “energy-momentum conservation.” It looks like this:

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    The details aren’t important, but the meaning of this equation is straightforward enough: energy and momentum evolve in a precisely specified way in response to the behavior of spacetime around them. If that spacetime is standing completely still, the total energy is constant; if it’s evolving, the energy changes in a completely unambiguous way.

    In the case of dark energy, that evolution is pretty simple: the density of vacuum energy in empty space is absolute constant, even as the volume of a region of space (comoving along with galaxies and other particles) grows as the universe expands. So the total energy, density times volume, goes up.

    This bothers some people, but it’s nothing newfangled that has been pushed in our face by the idea of dark energy. It’s just as true for “radiation” — particles like photons that move at or near the speed of light. The thing about photons is that they redshift, losing energy as space expands. If we keep track of a certain fixed number of photons, the number stays constant while the energy per photon decreases, so the total energy decreases. A decrease in energy is just as much a “violation of energy conservation” as an increase in energy, but it doesn’t seem to bother people as much. At the end of the day it doesn’t matter how bothersome it is, of course — it’s a crystal-clear prediction of general relativity.


    And one that has been experimentally verified! The success of Big Bang Nucleosynthesis depends on the fact that we understand how fast the universe was expanding in the first three minutes, which in turn depends on how fast the energy density is changing. And that energy density is almost all radiation, so the fact that energy is not conserved in an expanding universe is absolutely central to getting the predictions of primordial nucleosynthesis correct. (Some of us have even explored the very tight constraints on other possibilities.
     
  9. SimonsCat Registered Member

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    This is actually an important question; hard to answer.

    If there is not enough gravitational binding energy in the universe, then the universe may very well continue to expand forever. Consider that to make the temperature of a black hole go down, you need to add matter to the system. As the mass goes to infinity

    \(M \rightarrow \infty\)

    then equally temperature should approach zero (but probably never quite reach it due to zero point energy laws). For a black hole with infinite mass, the curvature will tend to zero. Isn't it striking that this should be more or less the definition of the vacuum!
     
  10. SimonsCat Registered Member

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    The only equation in relativity that conserves energy, believe it or not, is the Friedmann equation and is taken as an energy conservation equation.

    I don't agree with this approach. Friedmann only considered an adiabatic system because the universe should contain no true horizon (because a boundary implies it is a boundary between something and something else). We now know with the advent of field theory, we don't need an outside to a universe to actually change the energy of a universe.

    But yes, what you have stated is quite true: there is no conservation in general relativity because it lacks a definition of time. And without time, there is no translational conservation (Noether theorem).
     
  11. paddoboy Valued Senior Member

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    "What is striking is the fact that a BH with infinite mass is an invalid scenario and pseudoscience....Any BH can only have finite mass, although the singularity may lead to infinite quantities of spacetime curvature and density:
     
  12. SimonsCat Registered Member

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    What you were given was a thought experiment, not to be taken too seriously. However, it was supposed to be an interesting anecdote.
     
  13. paddoboy Valued Senior Member

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    I know what a thought experiment is, and I certainly did not take it seriously.
     
  14. SimonsCat Registered Member

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    I don't know why you seem to have an attitude, but here it is: Thought experiments, are not meant to be taken too seriously. They are designed to cause interest in a discussion, designed to cause critical thinking by drawing analogies and maybe paradoxes if you can.

    The universe is very similar to a black hole, outside the example I gave above. The early universe had a structure that was formally similar to how we understand the black hole today, and it has been expanding indefinitely ever since.

    Your objection to a black hole having infinite mass while not properly assessing that it was a thought experiment, is bunk.
     
    Last edited: Jan 20, 2017
  15. paddoboy Valued Senior Member

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    No, obviously it is a valid objection, despite your rather troublesome attitude.

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  16. SimonsCat Registered Member

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    I don't actually have an attitude, I was more thrown back by your aggressive reply while not fully thinking about what I said.
     
  17. paddoboy Valued Senior Member

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    Again, I know what a thought experiment is, and I certainly did not take it seriously.

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    Aggressive?

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    Just facts.
     
  18. Q-reeus Valued Senior Member

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    Yes some of us are aware that you recently 'discovered' Sean Carroll's take on cosmological energy balance or lack thereof. But you have for a far longer time been flooding this forum with similar bolded font full-reproduction of webpages advocating the very opposite, as I mentioned here: http://www.sciforums.com/posts/3413002/
    When are you going to come down from the fence and take a definite stand?
     
  19. SimonsCat Registered Member

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    ''his take'' as in Sean's take, isn't his take, by the way. It's Einsteins take. What Sean talks about on his preposterous universe blog, is already established science. Sean is just helping create interest in the area again by writing about it.
     
  20. Q-reeus Valued Senior Member

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    Yes I'm well aware Carroll never invented the idea, but my point was paddoboy doesn't seem to be aware of the contradiction in freely advocating that school of thought (which I side with), and the opposite one propounded by such folks as Philip Gibbs, Lawrence Krauss etc. Both camps claiming to be fully in accord with GR. I don't accept GR as fully self-consistent but that's beside the point here.
     
  21. SimonsCat Registered Member

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    What do you disagree with, non-conservation of a universe, perhaps? (rhetorical question for anyone)

    There are more reasons to believe the universe is not conserving energy, than is conserving it.
     
  22. SimonsCat Registered Member

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    Keep in mind, we only had a notion of conservation of energy in a universe because of the Friedmann equation, which through the equation of state, keeps energy the same in a universe, no matter what its size. The problem is that the universe is subject to quantum laws, and with the expansion of space, must come with it a violation of energy conservation due to vacuum fluctuations.
     
  23. SimonsCat Registered Member

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    Friedmann made the assumption (I presume) that a universe should remain constant with energy because it was and still is often modeled as an adiabatic system (no energy can enter or leave the system). But we don't need energy to enter or leave a universe any more, to actually change its energy content.
     

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