Space curved in on itself but with no Boundary & finite.

[Ron_refined]

Hello, I have some questions about General Relativity that I cant seem to get an answer.

 

I read possible the universe can wrap back in on it self, so if you looked far enough in one direction you could see the back of your head. So this is understood as the space warping in 3 Dimensions.

1- But if the space is really empty & not like a trampoline surface (in 2D), than can you explain how the space doesn't have an edge or boundary if finite in spacial extent? This really bugs me unless I'm missing something obvious?

 

I just don't know how a 3D universe that is curved having no boundary & being finite can be with empty space?

 

thanks

[michel123456]

I think it is about 4D spacetime, and not 3D space.

 

For example when you say (Bolded part)

 

Hello, I have some questions about General Relativity that I cant seem to get an answer.

 

I read possible the universe can wrap back in on it self, so if you looked far enough in one direction you could see the back of your head. So this is understood as the space warping in 3 Dimensions.

1- But if the space is really empty & not like a trampoline surface (in 2D), than can you explain how the space doesn't have an edge or boundary if finite in spacial extent? This really bugs me unless I'm missing something obvious?

 

I just don't know how a 3D universe that is curved having no boundary & being finite can be with empty space?

 

thanks

 

No, you will never see the back of your head, because what you see far away is also far away "in the past". it takes time for light from far away to reach your eyes. At best what you would see is an image of the point we are today as it was billion years ago. Certainly not the back of your head.

[elfmotat]

I'm not really sure what your question is...

[pmb]

Hello, I have some questions about General Relativity that I cant seem to get an answer.

 

I read possible the universe can wrap back in on it self, so if you looked far enough in one direction you could see the back of your head. So this is understood as the space warping in 3 Dimensions.

1- But if the space is really empty & not like a trampoline surface (in 2D), than can you explain how the space doesn't have an edge or boundary if finite in spacial extent? This really bugs me unless I'm missing something obvious?

 

I just don't know how a 3D universe that is curved having no boundary & being finite can be with empty space?

 

thanks

Above you said if the space is really empty. The space can have a density so small that its possible to have a straight line and not run into one of the particles in the space or you can take that one particle out of the way a bit.

 

 

What that means is that its possible to have a straight line (a geodesic in 3-d space) from the front of your head to the back of your head but not gonig through your head.

Edited May 16, 2012 by pmb