WannabeNewton said: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 said: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)?
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 said: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)
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.asimov42 said: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?
Correct! Lorentz invariance assumes a flat space-time. Any curvature, and it no longer holds.asimov42 said: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! ;-)
The rate of expansion of the universe is known as the Hubble constant, and it is currently estimated to be 73.3 kilometers per second per megaparsec. This means that for every megaparsec (3.26 million light years) of distance, the universe is expanding at a rate of 73.3 kilometers per second.
The rate of expansion of the universe is measured by observing the redshift of distant galaxies. This redshift is caused by the stretching of light as it travels through expanding space. By measuring the amount of redshift and the distance of the galaxy, scientists can calculate the rate of expansion.
The universe is expanding in all directions, meaning that every point in space is moving away from every other point. This is known as isotropic expansion. However, the expansion is not uniform and some regions may be expanding faster or slower than others.
Current observations and theories suggest that the universe will continue to expand forever. This is due to the presence of dark energy, a mysterious force that counteracts the pull of gravity and causes the expansion to accelerate. However, this is still an area of active research and our understanding may change in the future.
Dark matter, a type of matter that does not interact with light, is thought to play a significant role in the expansion of the universe. It is believed to make up about 27% of the universe's total mass, and its gravitational pull helps to slow down the expansion. Without dark matter, the universe would be expanding at an even faster rate.