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Author Topic: Does Dark Energy have selective effects?  (Read 3033 times)

Offline Joe L. Ogan

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Does Dark Energy have selective effects?
« on: 21/11/2009 15:09:45 »
Does Dark Energy (which used to be named Negative Gravity) have selective application?
It appears to affect inter Galaxies but has no apparent affect within the Galaxies.  In other words there is no expansion between the sun and the planets within our Galaxy.  Thanks for explanation.  Joe L. Ogan
« Last Edit: 25/11/2009 10:03:05 by chris »


 

Offline Mr. Scientist

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Re: Does Dark Energy have selective effects?
« Reply #1 on: 21/11/2009 15:15:27 »
It's really due to the fact expansion did not happen at one place alone. It was a big bang expanded equally and radially from every point in spacetime.

As dr Fred A. Wolf once said to me; ''You can think of these big bangs gang-banging into existence.''
 

Offline LeeE

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Re: Does Dark Energy have selective effects?
« Reply #2 on: 21/11/2009 17:43:31 »
The balance seems to be between 'dark energy' and gravity.

When it was first realised that the universe was expanding it seemed apparent that the rate must have slowed down from a previously higher value due to gravity: as gravity is a purely attractive force and must have been acting since matter existed, it must have had a slowing effect since then, which means that if it has been slowing things down up to now, then things must have been faster before.

However, while this still seems to be logically true, we now seem to be seeing an apparent increase in the rate of expansion i.e. there is something that is operating against the attractive gravitational force, and moreover, one that while sufficient to overcome gravity now, was insufficient to overcome it in the past.  One candidate for this is 'dark energy'.

Dark energy though, is very ill-defined; we have no direct evidence for it, and no real models of what it actually may be, or where it comes from.

Quite a few alternative and more prosaic explanations for the acceleration of the expansion of the universe also exist though.  For example, if new space is created at a uniform rate in 'empty' space i.e. space not occupied by matter, then this in itself will lead to an acceleration of expansion because there will always be more space to expand.  Another solution may lie in a consequence of Hawking radiation, where a slight imbalance between the numbers of oppositely charged virtual particles are acquired by the BH, resulting in a net overall charge to the universe, which would tend to force like-charged matter apart.  Both of these explanations would fit with the apparent 'S' shaped curve of the expansion rate: when the universe was much younger there would be both less space to expand, and there would be a lower net charge, so gravity could prevail and slow the overall rate of expansion.  As the universe has grown older though, there is now more space to expand and any charge may have increased, which may now be enough to overcome gravitational attraction, especially when combined with the fact that because everything is now further apart, the gravitational attraction is less.
 

Offline Geezer

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Re: Does Dark Energy have selective effects?
« Reply #3 on: 21/11/2009 19:18:16 »
For example, if new space is created at a uniform rate in 'empty' space i.e. space not occupied by matter, then this in itself will lead to an acceleration of expansion because there will always be more space to expand.

That's an interesting idea. A possible analogy is the way the continents are pushed apart as new seafloor is created in the Earth's oceans.

Personally, I find dark energy to be truly repulsive.
(apologies in advance)
 

Offline LeeE

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Re: Does Dark Energy have selective effects?
« Reply #4 on: 22/11/2009 12:07:38 »
Hmm.... with the mid-ocean rifts the new space is only created along the rift, which would be equivalent to constant expansion.
 

Offline Farsight

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Re: Does Dark Energy have selective effects?
« Reply #5 on: 22/11/2009 18:39:09 »
There is a way to understand it guys, and it's really simple. In general relativity the source of gravity is the stress-energy tensor, and Einstein said things like:

"This space-time variability of the reciprocal relations of the standards of space and time, or, perhaps, the recognition of the fact that ‘empty space’ in its physical relation is neither homogeneous nor isotropic, compelling us to describe its state by ten functions (the gravitation potentials gμν..."

Most people don't know what he meant here, and they miss the fact that a gravitational field is a region of inhomogeneous space. Whilst we tend to think of gravity as "negative energy", if you tested the Casimir effect at any location in a gravitational field, the plates will move together. There is no location where the plates move apart, and that's telling us that the stress-energy is positive at all locations. People ascribe this to virtual particles, but you have to remember these are virtual, and that vacuum energy is vacuum energy. It the energy of the vacuum, it's the energy of space. And since stress is the same as pressure, that means the "pressure" of space is positive at all locations. Think of a stress-ball, and squeeze it down in your fist. You put it under pressure, and when you let go, what happens? It expands. Now think of the universe as a ball of space. What happens? It expands, because space has this innate pressure.



The dimensionality of energy is pressure x volume, space has a pressure, and it certainly has a volume, so this means that dark energy is space itself. There's no energy outside the universe and so no space, so there's nothing to hold it in, hence it expands. There is the small matter of the vacuum catastrophe, but you can think of this as the difference between an expanding stress-ball and an expanding ball of compressed gas. If space didn't have a connected "elastic" quality that supported light waves, the universe would expand far more rapidly, just as a ball of compressed gas expands far more quickly than the stress-ball.   
« Last Edit: 22/11/2009 18:43:57 by Farsight »
 

Offline Geezer

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Re: Does Dark Energy have selective effects?
« Reply #6 on: 22/11/2009 18:47:39 »
I was about to post the followng when your post popped up. It may not be so different from what you are saying:

We "know" that matter interacts with space to produce gravity. Does matter apply some sort of "drag" on space? If so, it could tend to "glue" space together and prevent a natural tendency for expansion. In the absence of matter, space would continue to expand.

That would still leave a big question. "What is driving the expansion?"
 

Offline Farsight

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Re: Does Dark Energy have selective effects?
« Reply #7 on: 22/11/2009 19:29:37 »
Matter does apply some sort of "drag" on space, Geezer. It's a bit like sending in nanobots to stitch up microscopic internal portions of your compressed stress-ball so they can't expand. Then when you let the stress-ball go, it doesn't expand so fast because a percentage of it is bound up as matter. But note that it doesn't contract, just as the early universe didn't contract. And as to what's driving it, well, that's just how space is.

It's hard to describe succinctly, but space is kind of an elastic nothing. It isn't made out of particles, because something like a photon is like a ripple of spacewarp propagating at c, and an electron is what you get when this spacewarp travels through itself and warps its own path so totally it just goes round and round. A virtual particle is like a transient ripple of spacewarp. The thing is, space isn't "made" out of spacewarp. It's pretty unique stuff. It isn't made out of anything, instead everything is made out of it.   

 

Offline Geezer

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Re: Does Dark Energy have selective effects?
« Reply #8 on: 22/11/2009 19:50:36 »
I like that description, particularly the notion that everything is "made out of space". It also tends to explain why space is so elusive. The only tools we have to examine it are part of the thing we are trying to examine!
« Last Edit: 23/11/2009 05:55:47 by Geezer »
 

Offline Farsight

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Re: Does Dark Energy have selective effects?
« Reply #9 on: 22/11/2009 20:19:00 »
Exactly. That's why quantum theory is so difficult. Particles are described by the wave function, and people think it describes the probability of where you might find a point particle. But they forget about Weyl gauge-change and Schroedinger's equation and the way a photon isn't a point particle, because VLF radio can have a wavelength of ten kilometres. Then they forget that we use pair production to make an electron (and a positron) out of a photon, and they forget about deBroglie and his matter waves too. And gravity waves, see LIGO. It's all just "spacewarp", if you know what I mean.   
 

Offline Joe L. Ogan

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Re: Does Dark Energy have selective effects?
« Reply #10 on: 22/11/2009 20:24:05 »
You know, I have been thinking about this for quite awhile.  I now think that possibly space is not expanding at all.  It just gives the appearance of doing so because of the constant movement.  Joe L. Ogan




I was about to post the following when your post popped up. It may not be so different from what you are saying:

We "know" that matter interacts with space to produce gravity. Does matter apply some sort of "drag" on space? If so, it could tend to "glue" space together and prevent a natural tendency for expansion. In the absence of matter, space would continue to expand.

That would still leave a big question. "What is driving the expansion?"
 

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Re: Does Dark Energy have selective effects?
« Reply #10 on: 22/11/2009 20:24:05 »

 

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