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Creation of Energy in the Expansion of the Universe Violates Conservation of Energy?

  1. Mar 21, 2012 #1
    While researching dark matter and dark energy, I came across the following passage on NASA's website:

    "The first property that Einstein discovered is that it is possible for more space to come into existence. Then one version of Einstein's gravity theory, the version that contains a cosmological constant, makes a second prediction: "empty space" can possess its own energy. Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energy-of-space would appear."

    LINK: http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/


    In any high school physics class, we learn about the law of conservation of energy, yet this seems to violate it. Did I just misread the passage, or does this really violate the conservation of energy? If it does, how? If it does not, why?

    Also, how does empty space have energy? In order to have energy doesn't something have to be above absolute zero, and therefore be made up of matter (Or am I misinterpreting something)?

    If someone could explain this passage, it would be greatly appreciated!
     
  2. jcsd
  3. Mar 21, 2012 #2

    Drakkith

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    Re: Creation of Energy in the Expansion of the Universe Violates Conservation of Ener

    Conservation of energy isn't an easy thing to discuss in General Relativity. I've been in more than one thread about it so far, and the simple answer is "No, energy is not conserved on cosmological scales".
     
  4. Mar 21, 2012 #3

    Chronos

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    Re: Creation of Energy in the Expansion of the Universe Violates Conservation of Ener

    In GR the very definition of energy is unclear, so, how do you conserve that which is undefined?
     
  5. Mar 21, 2012 #4
    Re: Creation of Energy in the Expansion of the Universe Violates Conservation of Ener

    I'm a bit beyond my understanding on this but it may give others a starting point if I paraphrase something I saw posted by Lawrence Crowell who is a well known professional.

    The equation of state of the cosmological constant is w = -1 where 'w' is the ratio of pressure to energy density.

    http://en.wikipedia.org/wiki/Equation_of_state_(cosmology [Broken])

    If a force moves a mass work is done which means energy is supplied. If the presssure is negative, energy must be supplied, i.e. the contribution to the total is negative. If the value of w is exactly -1, the extra positive vacuum energy is exactly balanced by the negative contribution of expanding against the negative pressure. The measured value of dark energy is -0.980±0.053 so a value of -1 is consistent with observation.

    http://en.wikipedia.org/wiki/Lambda-CDM_model#Extended_models

    In other words, while it may be hard to define the total energy, a cosmological constant will conserve it while alternatives like quintessence may not.

    It is also interesting to note that the Hamiltonian for a closed universe is zero although it is hard to translate that to an open universe:

    http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html
     
    Last edited by a moderator: May 5, 2017
  6. Mar 21, 2012 #5
    Re: Creation of Energy in the Expansion of the Universe Violates Conservation of Ener

    This is really talking about vacuum energy which is more in the QM field:

    http://en.wikipedia.org/wiki/Vacuum_energy

    However, there is another aspect that is related to cosmology. Dark energy causes the expansion of the universe to accelerate and as a result light from very distant parts can never reach us, it creates a horizon. That is similare to the even horizon of a black hole. Hawking showed that a black hole's event horizon produces thermal radiation, it has a temperature. The same is true of the horizon in the universe created by accelerating expansion so even when all other matter has expanded so far apart that we cannot see it, a single particle remaining would be in thermal equilibrium with the temperature of the horizon. John Baez estimates around 10^-30K for that value:

    http://math.ucr.edu/home/baez/end.html

    Even a totally empty region of space would see that tempemperature as a surrounding spherical shell.
     
  7. Mar 25, 2012 #6
    Re: Creation of Energy in the Expansion of the Universe Violates Conservation of Ener

    would it be possible that, same matter is creating a gravitational field, the absence of matter is creating an anti-gravitational field ?
     
  8. Mar 25, 2012 #7
    Re: Creation of Energy in the Expansion of the Universe Violates Conservation of Ener

    No, the curvature is proportional to the energy/pressure so zero matter means zero curvature, no gravity. However, the cosmological constant does act like an anti-gravity term over very large distances because of the negative pressure. That is how it produces accelerating expansion.

    At least that's what I understand at present, as I say I'm a bit beyond my confort zone here.
     
  9. Mar 26, 2012 #8
    Re: Creation of Energy in the Expansion of the Universe Violates Conservation of Ener

    I see. would it be possible that its not 100% even, like in case matter and anti-matter reacted in the big bang, matter was left over. So it was not entirely symetric. In this case, is there a chance that there is a slight deviation in the linearity that might cause a weak anti-gravity effect ?
     
  10. Mar 26, 2012 #9

    Drakkith

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    Re: Creation of Energy in the Expansion of the Universe Violates Conservation of Ener

    Not according to current understanding.
     
  11. Mar 26, 2012 #10
    Re: Creation of Energy in the Expansion of the Universe Violates Conservation of Ener

    All measuremnents include some uncertainty. According to the WMAP site, the universe is flat to within ±0.5% so the total density probably between 99.5% and 100.5% of critical.

    http://map.gsfc.nasa.gov/universe/uni_shape.html

    This inventory shows the makeup of that:

    http://www.universetoday.com/92299/guest-post-the-cosmic-energy-inventory/

    Dark energy which can be thought of as creating "repulsive gravity" is 72% while all the rest is 28%, the overall effect being that the expansion of the universe is accelerating.
     
  12. Mar 26, 2012 #11
    Re: Creation of Energy in the Expansion of the Universe Violates Conservation of Ener

    i was thinking about light.
    a particle and/or a wave ?
    but what about darkness.?
    does darkness move at the speed of light?
    does light move at the speed of darkness?
    does light really bend around corners or is it pulled around by darkness?
    in a dark universe, does the universe expand when light appears?
    does light "push" darkness away ?

    i did post this on another thread by mistake.i got carried away reading all the interesting things here..
    so the universe expanding. all the dark energy moving outward to make room for the light popping up all over the place .maybe.

    but where is the line?
    the middle?
    between dark and light?
    there isnt one.i guess
    if so then they must join, interact which could then mean the universe is a one size universe amongst many verses.
    this could then mean it is getting smaller. this may explain the higher dark energy gravity...its getting squashed
     
    Last edited: Mar 26, 2012
  13. Mar 26, 2012 #12

    Drakkith

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    Re: Creation of Energy in the Expansion of the Universe Violates Conservation of Ener

    I replied to your post in the other thread. Hit up those articles and re-read them several times if need be.

    No, no light or matter is being created as the universe expands. In fact, light itself is losing energy as it travels the billions upon billions of light years due to the expansion of space. This causes it to become redder and redder, in many cases even enough to redshift completely out of the visible spectrum and into the infrared or beyond.

    As I said in the other thread, you misunderstand the standard model that cosmology uses to explain the universe. Hit up those links and browse around PF to learn more. You can use the Search function to search for posts relevant to this topic as well. (Although there is a LOT of them, so happy hunting)
     
  14. Mar 27, 2012 #13
    Re: Creation of Energy in the Expansion of the Universe Violates Conservation of Ener

    thanks for your reply .
    i have another question.
    i understand light loses its energy as it travels.
    but what im asking is ,can light just appear where there is no light?
    so as the universe expands light appears behind it making more galaxies which then expands the universe more..
    does the universe grow from the middle outwards or does it grow from any point within itself meaning that there is no center?

    i shall educate myself more .thanks for the links.
     
  15. Mar 27, 2012 #14

    Drakkith

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    Re: Creation of Energy in the Expansion of the Universe Violates Conservation of Ener

    No light is just created from nothing. The universe was once in a very hot, very dense state and expanded from there. The expansion happened everywhere and resulted in everything getting further away from everything else. There is no known center, and every point in the universe sees the rest of the universe expanding away from it at the same rate as all other points in the universe do. The current result of the expansion is the universe being in a less dense state that we see it in now. Existing light was redshifted as it traveled, but no more was created simply by the expansion itself.
     
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