The observable universe

[Cecil]

When you go straight out into space.

epepke was talking about the idea that the universe is spherical in the fourth dimension, so that living in it is like living on the surface of the spherical Earth - if you go far enough in one direction you will eventually come back to your starting point. Alternatively, we would be able to see our own galaxy somewhere in the sky if we looked far enough in any direction. This is not a generally accepted theory - most cosmologists believe that the universe is "flat".

That is why I can't wrap my head around most of this. There is an 'end' to earth, an 'end' to our galaxy, but not our universe?

Imagine the universe as an expanding bubble whose edge is growing outward at the speed of light. There is an "end" but you can never get to it, because it's moving away from you faster than you can get to it. In fact, even if you left here right now in a spaceship travelling at the speed of light, the closest "edge" would always be 13 Gly away. [/B][/QUOTE]

 

[patnray]

[QOUTE]Originally posted by epepke
It probably doesn't, because if the universe were infinite, and matter were roughly distributed in the universe, and roughly the same amount of matter were stars (which there's good reason to believe just happen due to gravity when there is enough matter), the night sky would be as bright as day. [/QUOTE]

Except for the big dust clouds that block light from getting through.

Except that the dust clouds themselves, being bombarded by bright light from every direction, would be hot and luminous. In a static and infinite universe the sky would be as bright as the sun in every direction.

 

[epepke]

epepke was talking about the idea that the universe is spherical in the fourth dimension, so that living in it is like living on the surface of the spherical Earth - if you go far enough in one direction you will eventually come back to your starting point.

Not necessarily a sphere, in fact probably not a sphere. My best guess is a projective plane crossed with a 3-torus.

Alternatively, we would be able to see our own galaxy somewhere in the sky if we looked far enough in any direction. This is not a generally accepted theory - most cosmologists believe that the universe is "flat".

Indeed, and I might be an idiot for thinking otherwise. But most of the views of cosmologists seem an odd mixture of classical and relativistic thinking to me.

 

[jj]

Not necessarily a sphere, in fact probably not a sphere. My best guess is a projective plane crossed with a 3-torus.

Alright, Eric, it's your fault. Now I need a BIG cup of coffee.