So we have evidence that stuff is moving away from something, but that relatively small chunk of the universe that we can see moving is not reflective of the rest of the universe, right?
It may or may not be. We cannot observe that which is unobservable (which is limited to the aptly named observable universe). Theories suggest that the universe is homogeneous on very large scales and these have held true for our observable universe: whether they're true for the universe beyond is anyone's guess, but logically it'd make sense if it was.
Think of it like two separate rooms in your house. You can observe the temperature, humidity, etc., of the room you're in. You can logically assume these factors are mostly true for the other room, even though quantum mechanically there's a chance that all the particles in that room's air have bunched up into a really small space. Possible but logic dictates it unlikely. Similarly while the universe beyond our observable universe could be really anything, logically the homogeneity we observe holds true for the rest of the universe.
Though ultimately:
or do we somehow have evidence that stuff outside of what we can observe is also moving away from the same point?
We really can't say for sure beyond logical deduction (i.e. not necessarily with evidence).
Though in the end science is a lot of "best guess," in a sense. Take gravity for example. First it was "everything goes down." Then Newton formalized it. Then it eventually got found inconsistent but became the basis for Einsteinian relativity. Science forms hypotheses and theories from observed data, and eventually theories become widely accepted; once found inconsistent a new theory, either modified or altogether new, is made. Science accepts what we see until we find something that invalidates it: it all builds on itself. Right now, a Big Bang theory is the predominant theory; one day, it might not be. Really just depends on what theory is the most evidenced, you know?
I get that the big bang isn't inconsistent with what we know, but I guess I don't see how that's is the leading theory right now when it's premised on the notion that everything is expanding, yet we don't know everything is expanding, or have any evidence for such a claim.
While I get your point, that kind of fallacy tends to invalidate all science. Going on the idea of an infinite universe, there's no way we can observe it all. How do we know that gravity simply doesn't stop working/works as we know it at extremely large distances, as an example? (This is a proposed explanation for dark matter by the way.)
Well, we don't.
But it's like "what we have does work." We have evidence and tested theories for all the stuff that gets widely accepted in science. And sure, it could all be wrong. We could live in a steady-state universe made by God for all we know. Perhaps the Big Bang never did happen and all the proof for it can be explained away by another theory or set thereof. And if so, science will change in line with that. Science is about developing and modifying theories: what we accept as likely today might be invalidated tomorrow. But we stick with what we know because it does work until then.
I'm not sure if I'm making sense at this point. I know what I'm trying to explain but I'm having a hard time doing so, I think, so I'll stop before I make things any more confusing.
@KeyBlade999 May I ask what you do? You did a phenomenal job breaking down the concepts into relatable concepts. Tbh I'm curious if you work in Acadmia because you would probably do quite well giving lectures.
Either way I thoroughly enjoyed your read an wanted to thank you. You cleared up a lot of confusion I had about certain aspects. ---
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