# Multiverse Questions

1. Jan 6, 2006

### Silverbackman

How can we say the universe is flat if it has depth? It may have very thin depth but it would mean that our universe is a rectangular cube, right?

Also If we were to theoretically go in a spaceship towards the ends of our fast universe, what then? Will there be powerful particles to halt us from leaving the universe? And what would lie directly outside the universe? Is it just empty space until we reach the next universes? Can we actually leave our universe?

Let us say we manage to leave the universe and we are in empty space. Would we be able to enter another universe if it is a sphere or would we be closed off? What about if it was a saddle universe? Or perhaps even a different shape universe is possible considering the different laws of physics.

2. Jan 7, 2006

### mathman

The term "flat" in describing the universe means that its curvature is 0, not that it is 2 dimensional.

Current models of the universe describe it as being without any boundary, so you second question is can't be addressed.

3. Jan 10, 2006

### Silverbackman

So in other words our telescopes have not reached to the very ends of the universe where we can see nothinging but "empty" space and no galaxies?

4. Jan 10, 2006

### mathman

The big bang occurred about 14 billion years ago. Therefore, the farthest distance which we could see is about 14 billion years. The cosmic microwave background (being extensively studied these days) is the residue of radiation from about 300,000 years after the big bang. That is the actual limit of visibility.

5. Jan 11, 2006

### Chronos

We are at the extreme edge of the observable universe. Do you feel any greater resistance when extending your arm in the 'direction' the universe is 'traveling'?

6. Jan 11, 2006

### Silverbackman

Mathman, but how do we know where the singularity is from? Does the singularity that is the source of all the matter and light (where the big bang occurred) in this universe from the edge of the universe surrounding it or is it in the center?? Where is the singularity to begin with? If we were to go in the direction light travels from would we reach the singularity?

Also, although our visibility maybe limited, what does it look like beyond the galaxies we can see? Is it just empty black space or the singularity?

Chronos, is our galaxy really at the extreme edge of the universe? How do we know this? And if so do we know what part of the universe we are at? If the universe is flat with a similar shape of a rectangle we can be "North", "South", "East", or "West" of the center of the universe right?

7. Jan 11, 2006

Staff Emeritus
The singularity is in everybody's past light cone. According to mainstream physics, we can't go there, no-one can.

The universe was opaque for some time after the singularity, according to standard cosmology, so there is no light directly from it. The CMB is radiation ("low frequency light") from the epoch when the early universe became transparent.

It has usually been assumed that our galaxy is not in any special position within the universe. Some recent speculations have us inside a bubble where the expansion characteristics are diferent from those outside the bubble. I don't think there is any evidence for a rectangular shape of the universe.

8. Jan 12, 2006

### Chronos

We are the most ancient object in our observable universe. That is indisputable. But, so is every other body in the universe in our 'now'. So, as SA pointed out, that is nothing special. In a relativistic universe, you must get accustomed to such concepts. It is very difficult to ascribe any particular geometry to the universe; in fact it's pretty much an exercise in futility. All such assumptions imply a preferred reference frame, and that option is virtually ruled out by observational evidence.