Rate and direction of expansion of the universe

[asimov42]

Hi all,

I was wondering: to the best of our current observational knowledge, is the rate of expansion of the universe the same in all directions in space? (I realize it varies in time)

 

[WannabeNewton]

If you choose your current location to be the center of the universe (you are free to do this because there is no true center) then all objects an equal distance radially from you will be receding at the same rate. The farther away these objects are the faster they will be receding so yes.

 

[asimov42]

Thanks WannabeNewton!

Are there any experiments underway or planned to try to distinguish between cosmological constant theories for the expansion and quintessence theories (with spatial variation)?

If you choose your current location to be the center of the universe (you are free to do this because there is no true center) then all objects an equal distance radially from you will be receding at the same rate. The farther away these objects are the faster they will be receding so yes.

 

[phyzguy]

Thanks WannabeNewton!

Are there any experiments underway or planned to try to distinguish between cosmological constant theories for the expansion and quintessence theories (with spatial variation)?

Yes! One of the stated goals of the BOSS project (http://www.sdss3.org/surveys/boss.php) is to measure the evolution of the expansion history of the universe to a high enough level of accuracy to see if there is any time variation of the cosmological constant. I think there are also projects to measure more distant Type 1a supernovae with the same goal in mind, but I'm not sure.

 

[Chalnoth]

Hi all,

I was wondering: to the best of our current observational knowledge, is the rate of expansion of the universe the same in all directions in space? (I realize it varies in time)

Well, it's a bit difficult to measure this with nearby objects, but our best observation for nailing this down is currently the WMAP observation of the CMB, which is uniform in all directions to one part in 100,000, which is strong evidence for expansion that is the same in all directions.

 

[asimov42]

Ok, so uniform expansion via the cosmological constant does not violate local Lorentz invariance - if it was discovered that the expansion was, in fact, non-uniform in space, would local Lorentz invariance be violated?

Also, just to clarify - global Lorentz invariance is already violated by the expansion of the universe, because the underlying metric is changing (due to the expansion of space)? Is that correct? Sorry for all the questions, still learning! ;-)

Thanks all!

 

[Chalnoth]

Ok, so uniform expansion via the cosmological constant does not violate local Lorentz invariance - if it was discovered that the expansion was, in fact, non-uniform in space, would local Lorentz invariance be violated?

Not at all. Local Lorentz invariance is a fundamental property of General Relativity. You'd have to have some (significant) deviation from General Relativity for local Lorentz invariance to fail. Simply having a non-uniform expansion wouldn't do that.

Also, just to clarify - global Lorentz invariance is already violated by the expansion of the universe, because the underlying metric is changing (due to the expansion of space)? Is that correct? Sorry for all the questions, still learning! ;-)

Correct! Lorentz invariance assumes a flat space-time. Any curvature, and it no longer holds.