Is the Universe Infinite or Just Expanding?

[calios]

guys I am quite interesting when some people talk about flat geometry universe they also relate this to spatially infinite universe..

well i don't fully grasp the idea,
but i try to imagine, when bigbang happened in infinite space, from observation scientist say there is no aether..they think we are in static universe, doesn't talk about boundary.. and later they found redshift and say we are in space expansion with boundary .. but can we say, it may not be the case?
what about we just explode in infinite space? we just thought the space is in expansion..
thank u

 

[Chronos]

In geometrical terms this means the ends of a line with no curvature [i.e., flat] will never meet. In cosmological terms this means you will never return to your departure point no matter how long you travel in one direction. This is not true on earth, for example. You will eventually return to your departure point if you travel long enough in the same direction [due to the curvature of the earth]. Expansion really has nothing to do with the curvature of space. You can still circumnavigate an expanding surface so it has any curvature. Scientists use conic sections to refer to curvature. A flat univese is a slice taken through the axis of the cone. It looks like a 'V'. A positively curved [closed] universe is a slice taken that intersects the axis. It looks like a circle or an ellipse. A negatively curved [open] universe is a slice taken that does not intesect the axis. It looks like a parabola or hyperbola. Both flat and negatively curved universes are considered infinite.

 

[bapowell]

A flat geometry can be bounded. The torus is one such example.

 

[Naty1]

talk about flat geometry universe ...

Well in many respects 'flat' versus 'curved' space [and time] is an idea I don't think many people even considred before Einstein. It's a crazy idea, if you ask me, but it works describing many observations and experimental results. Curved, warped time...what IS that?? It's another story, but you can check 'time dilation' in Wikipedia to get an idea about it.

well i don't fully grasp the idea,

not many do...that's because we don't have everyday experience with such an idea. New perspectives are one thing that makes science so interesting. You get used to seeing a house look smaller in the distance and experience shows you it is really bigger up close.

what about we just explode in infinite space?

while not necessarily impossible, that is not part of the best current scientific thinking.
The theoretical insights we have so far suggest that neither space nor time existed just before the big bang.

Here is a really nice introductory discussion; only five pages, but enough ideas for a lifetime!:

"Misconceptions about the Big Bang"
Baffled by the expansion of the universe? You're not alone.
Even astronomers frequently get it wrong

http://space.mit.edu/~kcooksey/teaching/AY5/MisconceptionsabouttheBigBang_ScientificAmerican.pdf