כנ"ל.
ובנוסף ראה תגובתו של מייק השקט. ומעוד לינק Until recently, it was not possible to determine whether the Universe is actually slowing by looking at the motions of the galaxies, because, as discussed above, galaxies which are far enough away so that their expansion velocity is much larger than their random local motions were too far away to make accurate estimates of their distances. So another method had to be used to determine what might or might not have happened since the Big Bang. That method involves looking at the amount of mass in the Universe to see if it is large enough to gravitationally slow the expansion. It is fairly easy to calculate (using the theory of General Relativity) just what density (mass per unit volume) the Universe has to have, in order to stop the expansion. If the observed mass is much less than this, then the expansion should never slow down. If the observed mass is much more than this, then the expansion should stop and reverse itself.
ובנוסף ראה תגובתו של מייק השקט. ומעוד לינק Until recently, it was not possible to determine whether the Universe is actually slowing by looking at the motions of the galaxies, because, as discussed above, galaxies which are far enough away so that their expansion velocity is much larger than their random local motions were too far away to make accurate estimates of their distances. So another method had to be used to determine what might or might not have happened since the Big Bang. That method involves looking at the amount of mass in the Universe to see if it is large enough to gravitationally slow the expansion. It is fairly easy to calculate (using the theory of General Relativity) just what density (mass per unit volume) the Universe has to have, in order to stop the expansion. If the observed mass is much less than this, then the expansion should never slow down. If the observed mass is much more than this, then the expansion should stop and reverse itself.