At what speed does the room expand

Is the universe expanding at the same speed everywhere in the universe?

We cannot say what lies outside the observable universe, but averaged over sufficiently large scales (≳ one billion light years) it does seem to expand evenly.

However, the presence of mass or general energy retards expansion. This means that on the scale of galaxy clusters, the universe expands more slowly, and on the scale of galaxy groups, the mutual attraction of the galaxies prevents them from receding from one another. This is also why our galaxy, solar system, planet and bikes are never torn apart (unless the cosmological constant is not a constant).

Conversely, at mass subdensities, ie the large voids between clusters and filaments of gas and galaxies, the expansion is increased (relative to denser regions). In fact, it has been assumed that the observed accelerated expansion of the universe is not due to dark energy, but could be an "illusion" if one accidentally lives in the center of a huge underdensity (e.g. Zibin et al. 2008). However, recent observations seem to rule out this possibility


Is the value of the Hubble parameter exactly the same everywhere in the observable universe? Or does it depend on the mass concentration in a certain zone?


@mick: The value of the Hubble parameter H.0 is an average of the entire universe, as it is calculated on the basis of several observables in all directions and at different distances. H.0 does not describe the rate of expansion in different regions of the universe, but the total rate of expansion. Local galaxies can recede from each other faster or slower than 68 km / s / Mpc, but the term H.0 describes the average rate of expansion at distances so great that particular speeds can be neglected (i.e. speeds due to local kinematics such as two galaxies, the circle each other).


For example, the space within the Milky Way does not expand. But we wouldn't say that H.0 = 0 in the Milky Way.


@JustinWaters: Not at all, you probably know more about science than I do about law :) Explaining the correct expansion of the universe takes a little more than what fits in a comment (I also have a deadline of 41 hours), but brief : Bras definitely cannot be the cause of expansion, although gravity actually does not "diffuse" linearly ("decrease" is a better word) (actually as the square of the distance). Bras, even the super massive ones, contribute relatively little to the total mass of a galaxy. (Continued in the next comment)


We do not see any expansion in the MW or in other galaxies, not even in those without central bras. And galaxies that are close together do not recede from one another either. However, we are seeing expansion on a larger scale. Galaxies that are far, far too far also feel the gravity of MW's BH at velocities that increase with their distance from us, linear at first, but not linearly as they reach great distances.