Redshift: A Hypothetical Question

[PoPpAScience]

I have a hypothetical question; now this is just a mind teaser.

If say, there was a centre to the Universe, and all the Galaxies were being drawn towards it. Would they still register as red shifted, if they were accelerating as they get ever more closer to the centre?

I have thought about this for a long time, maybe as long as 25 years. I am finally asking someones opinion, that may have a strong understanding of 'red shifts'.

Moderator note: this has been split off from the thread on primordial black holes

[neutralino]

Neutralino; I have a hypothetical question for you. Now this is just a mind teaser.

If say, there was a centre to the Universe, and all the Galaxies were being drawn towards it. Would they still register as red shifted, if they were accelerating as they get ever more closer to the centre?

I have thought about this for a long time, maybe as long as 25 years. I am finally asking someones opinion, that may have a strong understanding of 'red shifts'.

If there was a centre of the universe then there are two distinct positions in which we could be. Firstly, we could be at the centre of the universe. Now, we would see all galaxies around us accelerating towards us. This would result in a blueshift for every galaxy. The other position we could be is somewhere else away from the centre of the universe. Here, we would see a mixture: the light from some galaxies would be blueshifted, as they would be moving towards us, and some would be redshifted as they would be moving away from us.

For anyone else reading, who may not be 100% sure, I should point out that there is no centre of the universe, and so this is all hypothetical.

[Profpat]

I understand that they say there is no center Neutralino, But why not? Given the universe has mass why wouldn't there be a center of gravity. I understand it would forever be changing from frame of reference to frame of reference, but logically I would still think there should be one.

Please help.

Pat

P.S CONGRATULATIONS ON BEING A MODERATOR

[neutralino]

I understand that they say there is no center Neutralino, But why not? Given the universe has mass why wouldn't there be a center of gravity. I understand it would forever be changing from frame of reference to frame of reference, but logically I would still think there should be one.

Please help.

Pat

The short answer is that if the universe had a centre, then it would violate the cosmological principle. The cosmological principle basically says that we do not live in a special place in the universe; i.e. everywhere else is pretty much the same as where we are. If this didn't hold, then we wouldn't really be able to do cosmology, since the topology of the spacetime could be vastly different here than the rest of the universe. So, we say that the cosmological principle holds. There is, of course, vast evidence for this. See here for a fuller discussion.

And, thanks for your congratulations! It's the members that I should be thanking, though, for the interesting posts I've seen to respond to!

[Profpat]

Thanks for the quick response I'm going to have to read your link in detail.

Best,

Pat

[PoPpAScience]

The short answer is that if the universe had a centre, then it would violate the cosmological principle. The cosmological principle basically says that we do not live in a special place in the universe; i.e. everywhere else is pretty much the same as where we are. If this didn't hold, then we wouldn't really be able to do cosmology, since the topology of the spacetime could be vastly different here than the rest of the universe. So, we say that the cosmological principle holds. There is, of course, vast evidence for this. See here for a fuller discussion.

And, thanks for your congratulations! It's the members that I should be thanking, though, for the interesting posts I've seen to respond to!

Thanks Neutralino for the link. And starting this tread for me.

Do you realize that you gave me a link that says, if I was to state that Galaxies where residing to a centre, that my theory is as possible as any other. For all theories are limited to the scale of our observable Universe.

I especially like the example of Galaxies A, B, and C. If the words 'moving' were changed to 'receding', and the Galaxies were said to travel at an ever increasing speed as they move closer to the center, would not the example work the same.