To add to the other's comments. The redshifts observed and recorded are emprical facts. Vesto Slipher seems to be the first astronomer to get a number of these from nebulae (galaxies). It took Hubble to later determine that the nebulae were indeed galaxies, though he preferred not to call them galaxies.
Originally Posted by Olli S
I would think that the redshift as applied to galaxies would constitute a hypothesis, which are always based on objective evidence (ie redshift and other data). The time dilation in the light curves of certain supernovae also contributes objective evidence to the expansion hypothesis, which is part of the broader BBT (Big Bang Theory), of course.
Is the expansion of the universe also a fact because of the red shift, or is it an interpretation of this fact in the context of some model, theory?
The BBT begins from a tiny size just after a tiny fraction of a second past t=0, with an enormous expansion rate, which is now fairly steady though accelerating slightly, apparently. The question of what it may be expanding into is beyond science since this goes beyond all known observational possibilities.
How can the space of the universe expand when in the whole space of the universe there is already all the space that there is?
Last edited by George; 2017-Feb-13 at 08:47 PM.
We know time flies, we just can't see its wings.