Does the universe expand in every direction evenly?

Question

I've heard that the universe is expanding constantly and that galaxies are moving further and further away from each other because of this. However, does the universe expand in every direction evenly or does it expand in one direction more than another direction?

Answer 1

It is an assumption that the universe expands evenly in all directions, and the experimental evidence so far confirms the assumption.

Our mathematical description of the expanding universe is based on the assumption that on a very large scale the universe is homogeneous and isotropic, which basically means it's the same everywhere and in all directions. Since it's the same in all directions the expansion is the same in all directions.

I must emphasise the the homogeneity and isotropy is just an assumption that we make to make it easier to calculate how the universe expands. This assumption has to be checked by experiment to make sure it's correct. The main way this is done is by measuring the cosmic microwave background. If there were any anisotropies we would expect them to show up there, but we do not see anything that suggests an isotropy of the expansion. There are actually some weird things in the CBM e.g. the axis of evil. However opinion is divided about what exactly these obervations mean.

Answer 2

Short answer: Yes

Explanation: The answer to this question is something well documented in astrophysics. The "Size" of a universe is modeled by metaphorical expanding fluids known as the Freidman Equations. These equations say that from a singular point, the universe will expand at rates according to the travel of its components: energy and matter, for example, moving at different speeds. But each of the uniform types of matter expands with equal speed, so it becomes a matter of proportions to figure out the speed.

Answer 3

We believe that the universe expand in every direction evenly. Even-if there's any unevenness, it's hard to see, and will only be clear at very very large scales. Some people have combed the CMB (cosmic microwave background) and argue that there's maybe some evidence that things aren't perfectly even, but it's not really clear. Right now it really looks like the universe is expanding evenly in all directions, and any deviation from that is too small to be very clear.

More about it here and here

Answer 4

The fancy word for a Universe that expands equally in every direction is an isotropic Universe, and one that expands at different rates in different directions is anisotropic. The usual assumption is that the expansion rate is the same in all directions (i.e., the Universe is isotropic); this is the standard Freidman-Robertson-Walker metric for an expanding Universe, which seems to describe our Universe very well (so long as you postulate some mysterious forms of matter that you can't see, but that's another story.)

However, one can also consider the possibility that the Universe is spatially homogenous (meaning that the "local conditions" at every point in space are the same), but anisotropic. One can look for signals of anisotropic expansion in the usual sorts of places we look for clues about the expansion of the Universe: the cosmic microwave background, supernova data, etc. A recent analysis of data from the WMAP satellite concludes that it is highly likely that our Universe is expanding equally fast in all directions.