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Why is dark energy necessary?

  1. Oct 18, 2011 #1
    If the mass of the universe is constantly being converted to energy through nuclear fusion, and nothing can travel outside of space-time, then isn't the ratio of energy to mass increasing? If so, then wouldn't the only possible option be for an acceleration of the universe's expansion?
     
  2. jcsd
  3. Oct 18, 2011 #2
    Sorry if this was a stupid question. It just occurred to me that maybe the extra energy would be converted to mass in the form of the extra velocity of the matter in the universe. Maybe this cancels out the lost mass that used to be stored in the binding energy, which was released by the nuclear fusion. Is that it?
     
  4. Oct 19, 2011 #3

    mathman

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    Stars shine in all directions, so the energy can't be translated into a single direction.
     
  5. Oct 20, 2011 #4
    Stars shine their energy through space-time...
    Please explain your reference to "energy can't be translated into a single direction" , I don't understand, what direction are you referring to?
     
  6. Oct 20, 2011 #5

    phinds

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    I don't follow your logic at all. How would you propose that the reactions taking place inside stars creates an effect that spreads out evenly throughout the universe and causes the creation of space. I REALLY don't see how you get from one to the other.
     
  7. Oct 21, 2011 #6

    Chronos

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    I think not. By what process would that happen?
     
  8. Oct 21, 2011 #7
    The energy released through fusion has to go somewhere. Stars radiate their energy reasonably uniformly as far as I know. As the energy is released from the stars they lose mass. All stars are doing this, and they have been for quite some time. Since there is no space-time outside of the matter in the universe, that energy is contained inside the confines of that matter. I know I am not an astrophysicist, thats why I am asking the question.


    When particles are hit by photons, the particles get pushed slightly, if I am not mistaken. That energy keeps bouncing around, or being absorbed and then radiated, until it eventually is converted through those slight pushes on particles into mass again, in the form of velocity.

    The question is, with less mass over time, and more energy over time, why wouldn't acceleration be expected?

    Thanks for your replys phinds and Chronos, I can use all the help I can get :-)
     
    Last edited: Oct 21, 2011
  9. Oct 21, 2011 #8

    phinds

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    But the expansion of space is NOT "pushing" on anything, it's just creating space, which creates more distance between objects that are not gravitationally bound.

    The whole MECHANISM of "dark energy" just isn't what you seem to think it is.
     
  10. Oct 21, 2011 #9
    That is what I am saying. The photons released from the stars have a net effect of pushing against the other particles in the universe. The stars are all pushing against each other, and also against whatever other matter is around them. When a photon from one star hits a particle in another star, that is energy which helps to create more distance between them. The expansion of space is the particles pushing against each other, using the bonding energy released by nuclear fusion.
     
    Last edited: Oct 21, 2011
  11. Oct 21, 2011 #10

    phinds

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    As far as I'm aware there is no evidence to support this conjecture. LOTS of smart physicists have spent a lot of time trying to figure out what dark energy is and I don't find it believable that they have overlooked such a straightforward explanation.
     
  12. Oct 21, 2011 #11
    The OP isn't asking about dark energy though right? Just regular ol' run of the mill energy. He's proposing that dark energy doesn't exist.
     
  13. Oct 21, 2011 #12

    phinds

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    There is SOMETHING that causes the creation of space in between galaxies and thus causes an accelerating expansion of the universe. We call that something "dark energy" which is shorthand for "we have not a CLUE what is causing this". We see the effects, and as I said, lots of physicists spend lots of time thinking about what the hell it IS. There's a Nobel Prize in there for whoever figures it out first.

    The OP is suggesting that the accelerating expansion is not due to dark energy but is a result of a mechanism using existing mechanics that causes the stars to push against each other and that THIS causes the accelerating expansion. This completly overlooks the fact that in a universe with all the stars pushing against each other, none of them move as a result at all, much less expand, much less have an accelerating expansion. It just doesn't work.
     
  14. Oct 21, 2011 #13
    Right, I am just asking if there is all this energy being released by the stars, which would have to have an effect of expanding the universe, why is another form of energy needed? Unless all the energy of all the stars through all of time just isn't enough?
     
  15. Oct 21, 2011 #14

    phinds

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    But it WOULDN'T have that effect. What makes you think it would? What is the evidence?
     
  16. Oct 21, 2011 #15
    I thought they were moving away from each other, and thats why we need dark energy in the first place.
     
  17. Oct 21, 2011 #16

    phinds

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    our posts 12 and 13 crossed. What do you say to what I pointed out in post 12 ?
     
  18. Oct 21, 2011 #17
    That when a photon is released from one particle, and hits another particle, it causes the two to be pushed slightly apart.
     
  19. Oct 21, 2011 #18

    phinds

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    They are moving away from each other apparently as a result of the big bang. The velocity is ACCELERATING and that is what is attributed to dark energy. That is, dark energy is NOT why is causing the expansion of the universe, it is what's causing the expansion to accelerate.
     
  20. Oct 21, 2011 #19

    phinds

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    Further, the belief is that dark energy, whatever it is, has been around since the big bang, but it was only about 8 billion years ago that everything had spread out enough that it was able to start counteracting gravity and causing the expansion to accelerate instead of slowing down.
     
  21. Oct 21, 2011 #20

    DaveC426913

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    guys...
    The OP knows everything is moving away from each other. We all agree on this.

    The OP is positing that the output of stars pushes very other star away, having the net effect of everything moving away from each other. If this were the case, we would not need any form of exotic energy to explain the expansion we see.

    The question is: where is the flaw in his idea that EM radiation contains momentum, yet does not seem to push stars away from each other.
     
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