Perhaps the universe has already shrunk?

Answer

It is true that the further we look, the more we look into the past. At very great distances we do not see how the universe is expanding ‘today’, but how it expanded ‘then’. Only in our environment do we see the evolution of the universe today. And in that environment, we see that the universe is expanding today.

If your hypothesis that ‘today’ space collapses back ‘yonder’ is correct, then that would mean that two regions of the same cosmic time do not behave in the same way. An observer ‘over there’ would then see the universe collapsing in his environment ‘now’; he would see us as we were when the universe was as old to us as we see to him, and would perhaps see an expansion in us. So it would mean that different areas of the universe are different for the law.

Well, the basic principle of cosmology – the so-called “cosmological principle” – states that, at some point, the universe is broadly the same everywhere, in all directions. In a sense, this is a generalization of the Copernican principle, which states that there is nothing special about our position in the universe. It is not just a blind assumption, which would have been chosen to make our models simpler than necessary. No, it relies on observations. If we look in any direction in the universe, we will of course see other individual galaxies, but we always see the same picture overall on large scales: for the same cosmic time the same number of galaxies and the same size everywhere, also the same cosmological background radiation. This also means that an observer elsewhere also sees the universe the same in all directions. By the way, it is because of the cosmological principle that we can speak – not in contradiction with the theory of relativity – of a cosmic time (hence the quotation marks next to ‘now’ and ‘today’): indeed, since the universe expands in the same way everywhere, everyone can deduce from the density and temperature of the universe where he is situated in cosmic history.

Also the expansion law, Hubble’s law, is the same in all directions. If ‘today’ collapse is in progress at a certain distance in a certain direction, then it must be for all areas, in all directions, for that distance, otherwise we would see a different law of expansion in different directions. For two regions at that distance, which are also separated by that distance, Hubble’s law is then not the same in all directions, for everything in between them collapses, seeing an expansion toward us. And then we’re special again, and that’s unconstitutional in an astronomical context.