This has been puzzling my mind for a long time. How do we really know the universe is expanding? Based on observation? Redshifts? Observation based conclusions cannot be made IMO. We have observed the universe for a few hundred years and that is way too little to use to predict 13+ billion years. Redshifts are based on certain assumptions, IIRC even Hubble himself has pretty serious doubts. Furthermore, gravitationally bound galaxies *thus in proximity to each other* have demonstrated totally different redshift values, way out of what the values for galaxies that are supposed to be almost the same distance away should be. Everything in the universe seem to work in cycle manners, then why would the universe expand instead of for example, pulse in and out, and it just happens so that we live in a moment it is pulsing out? Also, if it is expanding, shouldn't we observe distant galaxies popping OUT of existence?