Did condensation accompany the initial big bang expansion?

[Loren Booda]

According to Newton's law of action-reaction, wouldn't a finite (non-singular) universe at the onset of the big bang experience condensation along with expansion? Could this duality be compatible with the cosmological principle of isotropy and homogeneity?

 

[SpaceTiger]

According to Newton's law of action-reaction, wouldn't a finite (non-singular) universe at the onset of the big bang experience condensation along with expansion?

Which "force" are you suggesting is being reacted to? The big bang doesn't apply a force to the universe in the Newtonian sense.

Could this duality be compatible with the cosmological principle of isotropy and homogeneity?

The nice thing about inflation (unless you're trying to test the theory) is that it doesn't matter how inhomogeneous things were beforehand, they still end up that way in the end.

 

[hellfire]

According to Newton's law of action-reaction, wouldn't a finite (non-singular) universe at the onset of the big bang experience condensation along with expansion?

The object which forces space to expand is a scalar field. This scalar field is (re)acted by the expansion giving rise to a specific spectrum of vacuum fluctuations. I am not sure this has something to do with Newton’s third law, but it sounds to me as something heuristically related to action and reaction.

The nice thing about inflation (unless you're trying to test the theory) is that it doesn't matter how inhomogeneous things were beforehand, they still end up that way in the end.

But one has to postulate the existence of some initial patch which must have been in some sort of equilibrium, as the exponential expansion of space does not favor the establishment of thermal equilibrium. However, the regions outside the patch must not have been in thermal equilibrium with the inner parts.

 

[SpaceTiger]

The object which forces space to expand is a scalar field. This scalar field is (re)acted by the expansion giving rise to a specific spectrum of vacuum fluctuations. I am not sure this has something to do with Newton’s third law, but it sounds to me as something heuristically related to action and reaction.

The fluctuations are associated with the pre-inflation vacuum and are quantum in nature. Inflation does not create these fluctuations, it simply freezes them and allows them to grow. I don't see where Newtonian action-reaction fits into this picture.

But one has to postulate the existence of some initial patch which must have been in some sort of equilibrium

Why do you say this must be the case? Based on observations, we can't really say anything useful about the pre-inflation universe, but if the Big Bang hypothesis is right, then it wouldn't have had much time to settle. It seems rather hasty to assume that any of it was in equilbrium.

I'm also not quite sure the connection you're drawing between this and homogeneity...

 

[hellfire]

The fluctuations are associated with the pre-inflation vacuum and are quantum in nature. Inflation does not create these fluctuations, it simply freezes them and allows them to grow.

I do not understand why do you write that these are fluctuations prior to inflation. To calculate how fluctuations are defined, how they evolve, their amplitude and how they are frozen, one has to define a quantum field theory of a scalar field in a de-Sitter background and find out (or actually define) the mode functions of the field expansion (the basis functions which are acted by creation and annihilation operators). These modes have a temporal evolution and some of them, at long wavelengths, freeze. These will determine the spectrum of density perturbations. Basically the whole issue here is a consequence of the QFT on a de-Sitter spacetime.

I don't see where Newtonian action-reaction fits into this picture.

Actually me neither, I was just speculating with the idea that the field causes expansion and expansion causes the specific shape or temporal evolution of fluctuations (or mode functions).

Why do you say this must be the case? Based on observations, we can't really say anything useful about the pre-inflation universe, but if the Big Bang hypothesis is right, then it wouldn't have had much time to settle. It seems rather hasty to assume that any of it was in equilbrium.

I'm also not quite sure the connection you're drawing between this and homogeneity...

Well I was talking only about thermal equilibrium. I thought we can assume a thermal equilibrium prior to inflation due to the causal contact with a very small scale factor. Are you telling me that if we assume a patch which is not in thermal equilibrium, inflation will lead to a thermal equilibrium between its parts?

 

[SpaceTiger]

I do not understand why do you write that these are fluctuations prior to inflation.

My point is that the fluctuations are there anyway, inflation or not. There are quantum fluctuations even in our own time, but because we're not undergoing exponential growth, they don't become frozen in. But this is a semantic argument -- my main objection concerned the action-reaction bit, and we seem to be agreed on that.

Well I was talking only about thermal equilibrium. I thought we can assume a thermal equilibrium prior to inflation due to the causal contact with a very small scale factor. Are you telling me that if we assume a patch which is not in thermal equilibrium, inflation will lead to a thermal equilibrium between its parts?

I suppose you're right that thermal equilibrium in the pre-inflation universe would be pretty much required to solve the horizon problem. I stand corrected.