B Is There a Reference Point for the Expansion of the Universe?

[Sarthak1221]

I once read somewhere a long time ago (and so I am not sure if this is true, let me know if it isn't) that the universe doesn't have a center of expansion. I get it. Neither does a typical balloon. But a balloon has an axis about which it is symmetrically expanding. Obviously that is not the case with the universe. So how exactly is the expansion taking place? Is there nothing that can be taken as a reference point for the expansion?

 

[phinds]

I once read somewhere a long time ago (and so I am not sure if this is true, let me know if it isn't) that the universe doesn't have a center of expansion. I get it. Neither does a typical balloon. But a balloon has an axis about which it is symmetrically expanding. Obviously that is not the case with the universe. So how exactly is the expansion taking place? Is there nothing that can be taken as a reference point for the expansion?

A reference point for the expansion would imply a preferred frame of reference and there is not only zero evidence for such, there is overwhelming evidence to the contrary.

Expansion has been beaten to death numerous times here on PF. I suggest a forum search.

I also recommend the link in my signature.

 

[Orodruin]

But a balloon has an axis about which it is symmetrically expanding.

No, it does not. You have to disregard any embedding of the balloon into three-dimensional space and just consider it as a two-dimensional surface. Anything outside of that surface is unphysical.

 

[phinds]

@Sarthak1221 I believe that you are referencing the entire volume of the balloon when you make your statement that it has an axis of rotation. What Ordruin is referencing when he says it doesn't have such an axis is the SURFACE of the balloon, which is what has to be considered if you are using the balloon analogy. Again, I suggest the link in my signature, which will explain that.