I've long wondered about an assumption that we have today and I've never found a direct answer to my question. Presently we can observe that there is a direct proportionality between an object distance and the factor by which its light is redshifted. We deduce that this observation implies that the universe is expanding. But is it really a scientific assumption to be made? Couldn't we equally extrapolate other plausible alternatives to explain an electromagnetic redshift without recurring to cosmological expansion? I've addressed this issue a few other astronomers and cosmology enthusiasts that I know, and the conversation always ends with the reference to the CMBR, but the way I see it, the CMBR is an entirely different phenomenon, all the CMBR really implies is that there is an almost uniform radiation being emitted from all directions, hence we infer that some time in the past the universe was a concentrated mass. Or in other words, the CMBR tell us that there was likely a big bang, but it doesn't tell us anything about cosmological expansion. Isn't this correct?