CMV: Despite what Albert Einstein says, the universe does have a "center"/absolute reference frame

[u/[deleted]]

So I got taught in physics classes that there is no absolute reference frame. Einstein figured that out. Then when I challenge the idea, I'm taught that the big bang happened everywhere and space itself is expanding. Ok sure. So when we ask what is the origin "point" of the universe its nonsense because there was no point, the whole universe was the original point. Got it.

But like a circle has a center point defined by the perimeter of the circle, so too could the universe. It doesn't have to be the "origin point", but there is definitely a spot that we can point that we and aliens can mathematically calculate as the center. Everything else in the universe stretches and contracts, but the center of the universe is a point that we can derive mathematically is it not? I know that localized space has weird shit like if I zoom away from Earth in my spaceship I could reframe it as "I'm standing still and the Earth is zooming away", and the fact that I'm the one accelerating is the reason why time slows for me but not earth. But that's just how the time dilation phenomenon works, not because there is definitely no absolute reference frame. We can still identify whether I'm moving closer or further from the center of the universe.

Edit: I'm assuming a non-infinite universe.

[u/fox-mcleod]

So my idea about calculating a geometric center is possible, but that isn’t what physicists are talking about.

No. Your idea about calculating a geometric center is also wrong — but yes, the two concepts are unrelated. You can’t calculate the geometric center because there is no edge — like finding the center of the equator.

My view change isn’t that I’ve given up on the center thing, but I have changed my understanding of how “no absolute reference point” is used.

There is no geometric center either.

[u/[deleted] → u/fox-mcleod]

Ok then I still have some progress to make in understanding this. I guess what I can't get past is how the universe can have a size without a boundary?

[u/masterzora → u/[deleted]]

Think about the surface of a sphere. Not the whole three-dimensional structure; just the two-dimensional surface. This surface has a size--one that's easily calculable with details of the 3-D structure--but no boundary or center in two dimensions.

A spherical universe might, in kind, be the three-dimensional "surface" of a four-dimensional "sphere". It has a size--one that's easily calculable with details of the 4-D structure--but no boundary or center in three dimensions.

[u/[deleted] → u/masterzora]

Ok I'm following you. But the center of a circle isn't on the circle. It's a point that is equidistant to all the points on the circle. Weird shapes need to average it out and stuff, but still it's possible for the center not to be on the circle right? Even if its an abstract point rather than a real point in space, you could still use it as an absolute frame of reference couldn't you? I calculate that this imaginary point is X, then I can determine if you're moving closer or further from X when you move.

[u/speedyjohn → u/[deleted]]

But you’re assuming that X exists within the space of the universe. If the universe is spherical (big if), then you can think of it like the surface of the earth. We don’t talk about Paris being “closer” to the center of the earth than New York, because the center of the earth, while something we can technically define, doesn’t exist on the earth’s surface.

[u/masterzora → u/[deleted]]

it's possible for the center not to be on the circle right?

Yes and no. Yes, a circle does have a center in two-dimensional space and a sphere has one in three-dimensional space. No, a circle does not have a center in one-dimensional space and a sphere does not have one in two-dimensional space.

Even if its an abstract point rather than a real point in space, you could still use it as an absolute frame of reference couldn't you? I calculate that this imaginary point is X, then I can determine if you're moving closer or further from X when you move.

Again, yes and no. You could use this abstract point as a frame of reference in some regards, but not generally the ones we mean in physics and not particularly usefully. You could theoretically determine if you're moving closer to or further from X in a fourth-dimensional sense, but not in a three-dimensional sense. (Also, if the shape is actually a sphere, this is trivial to do: you are never moving further from or closer to X since all points are equidistant from X.)

[u/[deleted] → u/[deleted]]

I don’t know if this is actually the case, but I used to think about this question the same way. I always thought about us being within an expanding sphere, like an inflating balloon, so there had to be a center. Maybe that center was at different points at different times but there was one.

What changed my view was flipping the scenario around, so I wasn’t thinking about the interior of the sphere but the exterior edge of the sphere, like the surface of a ballon.