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The source of dark energy

by DiracPool
Tags: dark, energy, source
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Feb17-13, 05:14 PM
P: 579
I want to get some opinions on what the source of dark energy is? I think there are basically two camps here. One camp says that dark energy originates from space itself, it is some perturbation in the quantum field whereby one cubic meter of space becomes 10 cubic meters somehow, and so on. The other camp would see it as the universe being "filled" by something external to it, like someone blowing air in a balloon.

The end effect of both scenarios would be essentially the same, a sphere of space-time blowing up and expanding isotropically and homogenously everywhere, but the fundamental sourcing of that expansion would be different.

I think the null hypothesis here is that the universe is being filled with something external to itself. One potential candidate is that our universe is being filled with space-time-matter-energy from the remnants of a black hole in another universe. This is the postulate put forth by Lee Smolin and his crew at the perimiter institute. But what are the arguments against this theory and what are the arguments for space itself expanding, which seems to me counterintuitive.
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Feb17-13, 09:55 PM
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marcus's Avatar
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"Dark energy" is an attractive name for something that we have no evidence is an energy.
It may tend to confuse and mislead people to use the word "energy" in this context.

There is no evidence that space is a material substance. Basically we are talking about geometry and the equations that have been proposed governing its development and change.

It is important not to take some traditional Greek idea of geometry for granted. We've discovered it changes according to its own law. We have no right to assume that angles of a triangle always add up to 180. The reason they do in some circumstances and do not in other is explained by the accepted law of geometry.We have no right to assume that distances once they start increasing will not continue to increase (even if "dark energy" or the cosmological curvature constant were zero). The gradual changes in the rate of increase are according to the accepted law of geometry.

We don't know that the law is absolutely correct. It's merely the best (most precise, widely applicable, simple, reliable) law of geometry we have so far. It works.
It might be improved some day but it is accepted for the time being. It has a curvature constant in it. So far there is no convincing evidence that attributes this constant to an "energy". The observational evidence has been running the other way---that it is simply a naturally occurring constant, like other basic physical constants. We will have to wait and see.

The cosmological constant Lambda (which some people call "dark energy") has so far played a very minor role. Even if that constant were zero, geometry would still be expanding. The mental image you offer of pumping something into space to make it expand is not a very good mental image. Geometry expands because that is what a lot of solutions to the GR equation do, and we happen to be in one of the expanding solutions. The equation has in it a natural tendency for processes like this to continue (though the rate may gradually change) without any outside input.

You might take a look at an article called "Why all these prejudices against a constant?" by Rovelli.
Just google "prejudices rovelli" and you should get it. If that does not work, please let me know.
Feb18-13, 03:42 PM
Sci Advisor
P: 6,070
The evidence that gives rise to this question is the fact that the expansion of the universe is accelerating. To account for this observation the idea of dark energy is proposed, along with a non-zero value for the cosmological constant. Anything more is speculative.

Feb26-13, 12:53 PM
P: 9
The source of dark energy

There are many quotations from the 19thC referring to the 'fact' that science was nearly complete except for a few minor bits to tidy up.
Is it possible then, that Dark Matter and Dark Energy are actually pointing to a 'new' physics where the Standard Model is a special-case subset of the Extraordinary Model or thanks to Godel are we going to be stuck in a self-referential loop of incompleteness?
I mean let's be honest. Just putting the word 'dark' in front of something doesn't explain it yet here we have 2 things accounting for most of the stuff in the observable Universe and we have no idea where they came from. Lambda, as a constant, was just shoved in there, taken out as a mistake then put back in when it was conveniently needed. Not much of a Fundamental principle.
Maybe Marcus is on the right track and everything is geometry, there is only one 'fundamental particle' (that kind of makes sense) only its not really a particle but a value (string?) in a particular dimension and it's the multidimensional tensor that determines the property that we call boson, fermion or even space (does a photon 'experience' time?) and so a particular combination that has a 'gravity' value accounts for the dark things.
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Feb26-13, 02:27 PM
Mordred's Avatar
P: 1,857
I certainly agree that geometry based proposals has strong merit. Though some of the geometry proposals vary in reliability.
As a result of another thread and looking into the premise of several of the inflationary models. Well lets just say that the vacuum to virtual particle models no longer is as viable as it once was since its first proposal. Least not in my humble opinion.
Mar3-13, 12:26 AM
P: 9
Maybe the observable Universe itself is a non-inertial reference frame and so the observations are a result of pseudo-forces?
Mar3-13, 02:26 AM
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Chronos's Avatar
P: 9,445
I agree with Marcus, there is no need to inject 'free energy' into empty space to generate a coordinate change.

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