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Message 3885 - Posted: 15 Nov 2007, 10:34:45 UTC

Could dark energy just be the energy in the space time dimension itself? I ask this because in my simplistic one dimensional view of space time I see gravity as the effect of distorting space time thus:-





Space time resists this distortion resulting in gravity, in other words space time wants to be flat.

The mass in the universe will cause a curvature of space time but if there has not yet been enough time for the actual curvature to grow to this size then there will be stored potential energy in space time, just like a spring. Could this be your dark energy? Whilst the curvature of the universe is greater than that necessary to balance gravity the effect would be to open out space time causing an acceleration in the expansion of the universe since it is the essentially the reaction force to gravity.

Clearly there is a flaw in this or Einstein would have thought of it as his explanation of the cosmological constant. The question is would I understand the flaw in my one dimensional view of space?

Dave.


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Message 4023 - Posted: 20 Nov 2007, 23:02:23 UTC - in response to Message 3885.  
Last modified: 27 Nov 2007, 22:40:18 UTC

Dave -

You are right, and right again, as it turns out Einstein did think of this. One way to model dark energy is in terms of an energy of empty space itself, or vacuum energy. Einstein introduced this concept in the form of a new constant of Nature, the cosmological constant, though when he introduced it he did it not to explain the acceleration of the Universe (which he did not know about) but as a way to stop the Universe from collapsing.

Einstein thought the Universe ought to be static and eternal. General relativity without the cosmological constant predicts an evolving (expanding or contracting) Universe. This was in conflict with Einstein\'s philosophical perspective and he found that by adding a term to his equations he could balance the Universe on a knife\'s edge between collapse and expansion. This is Einstein\'s famous \"greatest blunder\" - this is what he called his introduction of the cosmological constant because it prevented him from predicting the expansion of the Universe later observed by Hubble.

There are two major conceptual problems with interpreting dark energy as the energy of empty space: 1) while a vacuum energy is predicted by particle physics, the amount predicted is insanely higher than the dark energy, and 2) even if we just say that the cosmological constant is a new constant of Nature and do not try to explain it using particle physics, it hardly amounts to an explanation. The business of theoretical physics is to explain things in terms of more fundamental laws, thus reducing the number of parameters; not to keep adding parameters.

I comment more about these issues in my article on 2physics.com.

All the best,
Ben

PS: Re-reading your question, I now think that you I may have answered a different question than the one you asked. The equations of general relativity tell us how space-time reacts to mass and energy. What you describe should affect even a simple system such as a collapsing overdensity, since the mass distribution is changing and getting denser. It turns out that one can solve the GR equations exactly for the case of an infinite Universe that has a denser, collapsing region in it. In this case there is no acceleration of the Universe as a whole. So if I understand what you suggest it would require a modification to Einstein\'s equations and hence a departure from General Relativity. Then one would have to make sure that this modified theory still passes all the very exacting observational tests of GR in the solar system. But it sounds like your question is whether your idea is already contained in GR and if I understand your question correctly the answer is \"no.\"

Edit: just edited some words to clarify and a typo.
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