# The Observable Universe ve The Universe

1. Nov 9, 2013

### Nugso

Hello everyone. As I was reading an article on wiki, I stumbled upon this by chance;

If the universe is finite but unbounded, it is also possible that the universe is smaller than the observable universe. In this case, what we take to be very distant galaxies may actually be duplicate images of nearby galaxies, formed by light that has circumnavigated the universe. It is difficult to test this hypothesis experimentally because different images of a galaxy would show different eras in its history, and consequently might appear quite different. Bielewicz et al.:[13] claims to establish a lower bound of 27.9 gigaparsecs (91 billion light-years) on the diameter of the last scattering surface (since this is only a lower bound, the paper leaves open the possibility that the whole universe is much larger, even infinite). This value is based on matching-circle analysis of the WMAP 7 year data. This approach has been disputed.

(http://en.wikipedia.org/wiki/Observable_universe#cite_note-14)

Can anybody please explain the information above to me? I tried checking the references, but they didn't help me.

2. Nov 9, 2013

### phinds

I don't really know what you are asking. Do you understand the concept of a finite but unbounded universe?

3. Nov 9, 2013

### Staff: Mentor

A finite, unbounded universe can look a bit like the surface of earth. If you go in one direction long enough, you will reach your original position again (on earth, after ~40000km). The same could be true for light in the universe. We would see the same objects/structures in multiple directions. We do not, so apparently the universe is not smaller than the volume we call "observable universe".

4. Nov 9, 2013

### Nugso

Yes, kind of. Thanks to balloon analogy. What I'm pondering over is how the the text above can be possible?

@mfb

"We would see the same objects/structures in multiple directions."

Assuming I'm walking aroun the surface of earth, how could that happen? And also how do we know we don't know see the same objects/structures.

Thanks by the by!

5. Nov 11, 2013

### phinds

Then you have misunderstood the balloon analogy. It has nothing to do with whether the universe if finite/infinite and bounded/unbounded. I recommend the link in my signature.

6. Nov 11, 2013

### Staff: Mentor

You don't have to walk, light is coming towards you.

They would look the same?
Okay, more seriously, this would have been observed as structures in the cosmic microwave background.