Size of the universe - seeing yourself.

[Moonhawk]

I'm fairly well versed on all things astronomical and keep up to date on the latest developments in cosmology etc.

However I had a thought and although I have searched, I haven't found an answer to this.

If the universe is finite - then in theory if you travel in a straight line - eventually you'll end up back where you started (c.f. the surface of a balloon analogy). The same is true of a light beam.

The question I have is - is the universe in fact smaller than we think and when looking at something like the Hubble deep field - could we in fact looking at versions of our own galaxy from behind, but from earlier time in its history (a bit like on of those infinity mirrors).

I'm sure there is a theoretical reason why that is thought not to be the case - but I couldn't find any info on it.

[CrutyRammers]

I guess redshift would exclude that possibility? Everything we see (outside of our galaxy) is receding from us, whereas if we were seeing ourselves from behind, it'd be relatively motionless. I think.

[Simpo Two]

Moonhawk said:

If the universe is finite - then in theory if you travel in a straight line - eventually you'll end up back where you started

Or you go 'thunk' into a black wall...

[Moonhawk]

CrutyRammers said:

I guess redshift would exclude that possibility? Everything we see (outside of our galaxy) is receding from us, whereas if we were seeing ourselves from behind, it'd be relatively motionless. I think.

But that apparent recession is caused by the expansion of space time. Therefore even if we were seeing ourselves - the amount of space time the light will have had to travel through for us to see ourselves will have increased over time.

If we go back to the balloon analogy. We inflate the balloon half full and measure the distance to various points on its surface - including measuring all the way around the balloon back to ourselves. We then inflate the balloon to double it's size - all of the distances we measured will have increased. We will have appeared to have moved away from ourselves because the space time the light has had to travel in order to get back to ourselves has expanded.

Edited by Moonhawk on Thursday 26th February 16:44

[TwigtheWonderkid]

Simpo Two said:

Moonhawk said:

If the universe is finite - then in theory if you travel in a straight line - eventually you'll end up back where you started

Or you go 'thunk' into a black wall...

Yes, like on The Truman Show!

[Simpo Two]

Talking of scale, I seem to recall a programme many years ago which stated that the thing halfway in size between the smallest object and the largest (ie the universe) is a squirrel.

Logarithmic perhaps?

[TwigtheWonderkid]

Simpo Two said:

Talking of scale, I seem to recall a programme many years ago which stated that the thing halfway in size between the smallest object and the largest (ie the universe) is a squirrel.

Red or grey?

[Simpo Two]

TwigtheWonderkid said:

Red or grey?

I don't think it specified the colour. But if it was grey, then the universe is bigger than we thought...

[type-r]

Simpo Two said:

Talking of scale, I seem to recall a programme many years ago which stated that the thing halfway in size between the smallest object and the largest (ie the universe) is a squirrel.

Logarithmic perhaps?

Am sure this has been posted before:

http://htwins.net/scale2/