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How much energy is there in the Universe?

  1. Aug 23, 2012 #1
    How much energy is there in the universe?

    I've heard a lot of people saying the total amount of energy in the universe is 0, if this is the case the total amount of mass in the universe is 0. In this scenario there is an equal and opposite amount of mass/energy in the universe. How would the "negative" mass/energy act? It would need to be something when brought in contact with "positive" mass/energy would exactly annihilate each other and bring the system back to a state of 0 (with no "positive" or "negative" fluctuations). Do we see anything of this nature? Upon first look it seems like a weird concept both required and disallowed by the laws of physics, but I have the sense that I'm just not look at it from the right perspective yet.

    Thanks for your help!
     
  2. jcsd
  3. Aug 23, 2012 #2
    I don't understand it, but the basic idea is that gravity is negative.
     
  4. Aug 24, 2012 #3

    Drakkith

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    To take into account ALL of the universe we need to use General Relativity and it's math to describe it. Unfortunately there is no specific definition of energy that is fully accepted in General Relativity, so it makes it difficult to answer you. On top of that, different ways of "setting up the problem" changes things also. I know there is one "solution" if you will that says that the total energy of the universe is 0, however this is only one possible solution.

    I can't explain it very well, but I know we have a thread or two here on PF about it. Try using the search function to find it.
     
  5. Aug 24, 2012 #4
  6. Aug 24, 2012 #5
    Another bit of evidence is that the universe exists at all. Only a zero energy universe can spontaneously pop into existence without violating conservation of energy.
     
  7. Aug 24, 2012 #6

    Drakkith

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    Doesn't the universe ignore the conservation of energy as a whole? Take a look at the CMB. It's losing energy as time passes without that energy showing up somewhere else.
     
  8. Aug 24, 2012 #7
    I think it's losing positive and negative energy at the same rate. Otherwise the universe would not remain flat.
     
  9. Aug 24, 2012 #8

    Drakkith

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    How is it losing negative energy?
     
  10. Aug 25, 2012 #9
    A gravitational field is a form of negative energy. Imagine you had a single planet somewhere alone in space. Far away from any galaxies. Now on this planet you have a matter to energy converter that consumes matter and releases photons. These photons are then send into space in form if a laser beam. Far away from that planet there is a photon to matter converter that receives the laser beam and turns it back to matter. As the photons move away from the planet their wavelength increases due to gravity which means they lose energy. As a result the amount of matter created by the photon to matter converter is smaller than the matter lost by the planet. Positive energy is being lost. Seemingly vanished into nowhere. But at the same time the gravitational field around the planet has decreased, so an equal amount of negative energy was lost as well.
     
  11. Aug 25, 2012 #10

    Drakkith

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    I understand your example, but consider that expansion causes even further energy loss of radiation as time passes. If your photon-matter converter was far enough away so that expansion caused it to recede from your planet then it would produce less and less matter over time as the photon energy falls. This energy is simply gone.
     
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