Is Dark Energy Consistent with a Cosmological Constant?

[Sariaht]

So since it decay, it is constant, ie. if vacuum has energy, it is constant since the original state 1 of the universe, is derived from its original properties k1, k2, k3...

If these properties of something that did not yet exist, were true for that which the universe was defined as being that which does not exist, the decay of that which does exist will cause the original properties. Hence cc.

Is there something I'm missing. SpaceTiger, what are the actual facts in the matter?

 

[SpaceTiger]

Is there something I'm missing. SpaceTiger, what are the actual facts in the matter?

I'm sorry, Sariaht, I don't know what you're trying to say. I suggest studying up on GR a bit...Gokul's link https://www.physicsforums.com/showthread.php?p=1169553#post1169553" wouldn't be a bad place to start.

 

[Mike2]

But this is precisely why a false vacuum energy and a zero-point energy are not the same thing. A false vacuum energy is not the true zero point -- it is due to a scalar field that has kinetic energy and can decay. The difference between this and the cosmological constant is that the energy density is not constant. It is approximately constant throughout most of inflation, so during this time, the behavior of the universe will be nearly identical to that under a pure cosmological constant.

If the current acceleration were due to a false vacuum state (still a possibility), then we would expect it too to eventually decay, in contrast to the standard \Lambda CDM model. As I said before, the cosmological constant can be due to a non-zero ZPE (the true vacuum state), or it could simply be an extra integration constant in GR. Since GR still obeys the equivalence principle with the inclusion of the cosmological constant, it's just as good a theory of gravity as one with zero CC. This latter possibility is what I was referring to in the post you quoted and it really has nothing to do with inflation.

Actually, I'm not sure that whether the vacuum energy is the zero point of a quantum field or not is relevant to the question. I think all that is relevant is what is the vacuum energy at a particular time. Isn't the vacuum energy (whether false, true, or whatever) equivalent to the average energy density that exists for a given amount of time? Doesn't the vacuum energy define the amount of uncertainty in Heisenberg's uncertainty principle? If so, then doesn't a higher vacuum energy mean that h-bar was higher than otherwise? Thanks.

 

[SpaceTiger]

Actually, I'm not sure that whether the vacuum energy is the zero point of a quantum field or not is relevant to the question.

I wasn't responding to your question, I was responding to the passage I quoted.

I think all that is relevant is what is the vacuum energy at a particular time. Isn't the vacuum energy (whether false, true, or whatever) equivalent to the average energy density that exists for a given amount of time? Doesn't the vacuum energy define the amount of uncertainty in Heisenberg's uncertainty principle? If so, then doesn't a higher vacuum energy mean that h-bar was higher than otherwise?

It's not clear to me what that would mean, since h-bar has units. We generally only consider the time-variation of unitless quantities, like the fine structure constant.

 

[Mike2]

It's not clear to me what that would mean, since h-bar has units. We generally only consider the time-variation of unitless quantities, like the fine structure constant.

We 'are talking about the priod of Inflation before the Standard Model was in effect, right? So I suppose anything's possible there, including a different speed of light, etc.

 

[SpaceTiger]

We 'are talking about the priod of Inflation before the Standard Model was in effect, right? So I suppose anything's possible there, including a different speed of light, etc.

I suggest you take a look at this paper:

http://www.arxiv.org/abs/hep-th/0208093"

If you're wondering why we still discuss variable speed of light cosmologies, it's because they propose a change in the laws of relativity (they actually break Lorentz invariance), not just a simple change in c.

 

[Sariaht]

I suggest you take a look at this paper:

http://www.arxiv.org/abs/hep-th/0208093"

If you're wondering why we still discuss variable speed of light cosmologies, it's because they propose a change in the laws of relativity (they actually break Lorentz invariance), not just a simple change in c.

Ok, your post can be missunderstood, what breaks what?

 

[Mike2]

I suggest you take a look at this paper:

http://www.arxiv.org/abs/hep-th/0208093"

If you're wondering why we still discuss variable speed of light cosmologies, it's because they propose a change in the laws of relativity (they actually break Lorentz invariance), not just a simple change in c.

Haven't read it yet, I intend to look at it. But I have to ask if they are still talking about the moments during Inflation. Correct me if I'm wrong, but I thought Inflation is a time before the GUT and the SM, etc. As such the fundamental constants based on mass and time, etc, would not be calculatable yet. As I understand it, the laws of physics as we understand them today did not apply in the moments of Inflation. For Inflation involved quantum fields in some sort of symmetric state that broke down after Inflation to give us the SM on which the dimensional constants rely. If the Inflaton field decayed to give us the mass of particles, then how would one calculate the constants that involve mass before there was mass. And if something as fundamental as mass of a particle can change (as it comes into existence), then I would think that would certainly leave open the possibility of changing c or h-bar, etc. Am I understanding things correctly here? Thanks.