Hey duder,

Redshift and expansion are intrinsically linked, yes?

Yeah, our best evidence for the inflation/expansion of spacetime is the fact that we observe every galaxy receding away from our respective (as I’m sure you know, things travelling “away” from you are redshifted, things travelling toward you are blueshifted) indicating that either the Milky Way galaxy really is in the center of the universe (basically geocentrism ) or that perhaps there’s “no such thing” as the center of the universe, and everything is receding from everything else which is the standard interpretation of the data, so-called cosmic inflation or expansion

And I agree, it’s one thing to believe something strongly based on evidence, but so much of science is strong belief based on philosophy, which is to say, people rule things out which fit the evidence but don’t fit their preconceived bullshit way too readily.

I was reading about this yesterday and came across a great comment:

The cosmological models are based off two assumptions, that the universe is homogeneous at large scales and that the universe is isotropic at at least a single point. These assumptions essentially mean that the universe looks the same wherever you are. These assumptions are supported primarily by observation of the CMB. However, the evidence does not rule out a geocentric universe. Indeed, the evidence certainly seems to imply that Earth occupies some special place in the universe. When we combine the CMB observations with the observation that other galaxies seem to be receding from us, there is a lot of support for a geocentric model. It is very easy to think that the geocentric model is the only possible model. However, of course, there is a perfectly good alternate explanation, the one I gave initially, that the universe is homogeneous and isotropic. In particular, as implied by this model, any other galaxy also sees all other galaxies receding from it.

So what makes us choose the current model over geocentrism? We appeal to the so-called Copernican principle, which states that Earth is not in some special, preferred position in space. Earth is not the center of the universe. You will also read this principle as "humans are not privileged observers". This principle rules out the geocentric theory entirely.

It is crucial to understand that there is no evidence for or against the Copernican principle. (That is not to say that there is not evidence that supports the principle, but the geocentric model is an alternate model which is also consistent with the evidence.) Of course, there is good reason to believe it. A principle of modesty is also often invoked, since it would be incredibly remarkable if the Copernican principle were not true. But there is no way to decide based on observed evidence. We are using a fundamentally philosophical criterion to choose our cosmological model. There is nothing wrong with that per se, but it certainly does lead to many interesting questions in the philosophy of science.