[JustinW]

I've been wondering about the expansion of space and the relation to the pressure of space. After reading about the cosmological constant and other things I had questions that I have been unable to find an answer to. I was wondering if the expansion of space and the pressure of space were related? If they're not then why not? I can't seem to find any information about the measurements of the vacuum pressure over an extended period of time to indicate any change in that pressure. To my way of thinking the pressure should correlate with the rate of expansion.( Assuming the two are related. Which I can't see why they wouldn't be.) I was also thinking that gaining an accepted measure of study on pressure changes would tell us what the universe is doing as whole. Not just in our range of observation. It would make sense that if the pressure was to grow stronger (more negative) then our universe is expanding. If the pressure grew weaker (more positive) then our universe is contracting. If the pressure stays the same (with reasonable fluctuations) then we could assume that our universe as a whole is static, but that with in is just in motion. Now all of this is under the assumption that pressure and expansion are related. The reason I believe they are is because the way a vacuum is created. The less matter you have in a space the more of a vacuum is created. We know that space has a vacuum energy, so it could be assumed that that is because of the amount of matter that is in the space. Possibly created in the original expansion. If it is space that is expanding, then the less matter should be in that space as it grows, therefore should affect the pressure of that space. At least up until an absolute perfect vacuum is achieved. Let me know what you all think about this assertion and if there is any info out there related to this connection.

[JustinW]

Due to the lack of response to this topic it seems as though this topic is either lacking in substance or lacking in some other ways. I just recently had a conversation that might have changed my views when looking at space and pressure and the relationship between the two. Someone was trying to argue that space was a physical entity, which I don't necessarily agree with. But it seems that the relationship between space and pressure are one and the same, and that in fact space defines pressure. The less space you have in area the more possitive the pressure is, and visa versa, the more space you have the more negative a pressure is. If this is true then it would fall back to my origional question above as to how this relates with the expansion of our universe. Just some extra thoughts I had about space and pressure being a reflection of one another. Comments are welcome.

[DrRocket]

JustinW, on 11 January 2012 - 05:56 PM, said:

I've been wondering about the expansion of space and the relation to the pressure of space. After reading about the cosmological constant and other things I had questions that I have been unable to find an answer to. I was wondering if the expansion of space and the pressure of space were related? If they're not then why not? I can't seem to find any information about the measurements of the vacuum pressure over an extended period of time to indicate any change in that pressure. To my way of thinking the pressure should correlate with the rate of expansion.( Assuming the two are related. Which I can't see why they wouldn't be.) I was also thinking that gaining an accepted measure of study on pressure changes would tell us what the universe is doing as whole. Not just in our range of observation. It would make sense that if the pressure was to grow stronger (more negative) then our universe is expanding. If the pressure grew weaker (more positive) then our universe is contracting. If the pressure stays the same (with reasonable fluctuations) then we could assume that our universe as a whole is static, but that with in is just in motion. Now all of this is under the assumption that pressure and expansion are related. The reason I believe they are is because the way a vacuum is created. The less matter you have in a space the more of a vacuum is created. We know that space has a vacuum energy, so it could be assumed that that is because of the amount of matter that is in the space. Possibly created in the original expansion. If it is space that is expanding, then the less matter should be in that space as it grows, therefore should affect the pressure of that space. At least up until an absolute perfect vacuum is achieved. Let me know what you all think about this assertion and if there is any info out there related to this connection.

Pressure is probably a factor in the accelerating expansion of space, but not in the way that you think.

Pressure enters into the Einstein field equations of general relativity that determine the curvature of spacetime which in turn results in what is commonly called "gravity". But pressure results in a postive gravitational force, rather than what is required to cause accelerating expansion -- a repulsive force.

However, the energy of the vacuum, as predicted by quantum field theory, would result in a negative pressure which in trun would provide the required negative presssure which is equivalent to a positive cosmological constant, which is effectively a repulsive force.

Unfortunately current estimates of the cosmological constant, based on the energy of the vacuum according to quantum electrodynamics, overestimate the observed cosmological constant by a factor of about -- probably the all-time record for a misprediction in all of physics. No one understands this.

[JustinW]

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Unfortunately current estimates of the cosmological constant, based on the energy of the vacuum according to quantum electrodynamics, overestimate the observed cosmological constant by a factor of about -- probably the all-time record for a misprediction in all of physics. No one understands this.

Yes, I've heard this a time or two. This is why I have doubts about there being a cosmological constant and even doubts about the universe expanding. I know that the expansion has been observed. But the fact is that if expansion doesn't directly coordinate with the pressure of space then by rights there should be another explanation for what we've observed, or there should be an explanation of why the pressure has no connection to the expansion.

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Pressure is probably a factor in the accelerating expansion of space, but not in the way that you think.

I wasn't meaning to imply that negative pressure drives expansion.

I was looking at this in a way that the pressure of space was a result of expansion, instead of a cause or fuel to the expansion. My general thinking on this still allows for the theory of dark energy or anti gravity as a means of driving the expansion, but that expansion itself would have a direct effect on the overall pressure of space.

Like in the Cassmir effect experiment or the mechanics of a pressure chamber. To create a negative pressure you would have to remove matter from space. Looked at from the view of an expanding universe we are essentially doing that by a growing amount of space to matter ratio. (Assuming that the universe as a whole is a closed system) Wouldn't that have a direct effect on the pressure of space and therefore be measurable? If this was the case then it would tell us how our universe is acting as a whole, and not just in what we are able to observe.

This post has been edited by JustinW: 26 January 2012 - 09:21 PM

[MigL]

Yet negative pressure could drive expansion, and at the very least is postulated by Guth to have driven inflation. If the universal vacuum energy 'hung up' at a false ( higher than ) zero level just after the big bang, it would have experienced violent inflation while it slowly fell to the actual zero point vacuum energy. If it never actually reached the zero point, but just drastically slowed down its descent ( much lower slope ), then it could still be driving expansion at a much reduced rate, ie. accounts for the cosmological constant.

But I guess that unless we can get a handle on a realistic value for the vacuum energy, all this is just speculation,

[JustinW]

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But I guess that unless we can get a handle on a realistic value for the vacuum energy, all this is just speculation,

My point exactly. I want to know why it is that we only use estimates for the vacuum of space and not an actual physical measurement. Surely we are capable of such an achievement. We seem to be spending most of our time with what we observe rather than what we can test.

I just had a second thought. Pardon me for being a lack wit. When someone tests light in a vacuum, at what level of vacuum do they test? And does that have any coorolation with the vacuum of space?

This post has been edited by JustinW: 27 January 2012 - 01:34 PM

[Airbrush]

Is dark energy the result of a total vacuum beyond our visual horizon? A total vacuum would accelerate expansion and maybe explain dark flow. There is no total vacuum anywhere we can see. What do you think?

This post has been edited by Airbrush: 27 January 2012 - 07:01 PM

[JustinW]

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Is dark energy the result of a total vacuum beyond our visual horizon? A total vacuum would accelerate expansion and maybe explain dark flow. There is no total vacuum anywhere we can see. What do you think?

I don't think so, we can observe things being affected by dark energy, such as the expansion of super clusters. I don't think that dark energy and vacuum energy are the same. (if such thing as dark energy exists) Dark Energy is just a name we use for something that we can't see. We just observed the result and labeled the cause as Dark Energy until we can learn more. It would only make sense that the universe has an overall pressure (assuming the universe is a closed system) and being able to measure that pressure would theoretically tell us exactly what the universe is doing as a whole. At least that is what I think until someone can redirect my thinking with a logical reason of why it doesn't work that way. (which happens more often than not.)

[guenter]

Airbrush, on 27 January 2012 - 07:00 PM, said:

Is dark energy the result of a total vacuum beyond our visual horizon? A total vacuum would accelerate expansion and maybe explain dark flow. There is no total vacuum anywhere we can see. What do you think?

No, vice versa. Some researchers discuss the possibility that we are in the center of a low matter density region. Imagine the galaxies beyond the visible universe to be spherically symmetric much more dense, then the galaxies within the visible universe would recede accelerated as observed. However having the copernican principle in mind this sounds not too trustful.
Assuming vacuum outside one would rather expect deacceleration or even contraction.

[DrRocket]

Airbrush, on 27 January 2012 - 07:00 PM, said:

Is dark energy the result of a total vacuum beyond our visual horizon? A total vacuum would accelerate expansion and maybe explain dark flow. There is no total vacuum anywhere we can see. What do you think?

Nobody has a clue as to the source of dark energy.

A total vacuum would most certainly not accelerate expansion and it has nothing whatever to do with dark flow.

The energy of the quantum vacuum is predicted to accelerate expansion. The problem is it overpredicts the expansion rate by a factor of
10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

[JustinW]

Here is an article that was provided in another thread that I thought was interesting and I think relevant to the subject to some degree.

http://discovermagaz.../vacuummatters9

[guenter]

DrRocket, on 28 January 2012 - 11:50 PM, said:

The energy of the quantum vacuum is predicted to accelerate expansion. The problem is it overpredicts the expansion rate by a factor of
10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

That seems not compelling. This catastrophic factor was calculated from QFT as the sum of zero-point energies. They could gravitate as well.

On the other side this factor isn't a real problem, because you can get rid of it by renormalization. What remains to be argued are differences of energy, a good example for which is the Casimir-effect.

Some hope comes from LQG to at least model the inflationary period of expansion.