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 [quote="Antrax"]The radius of the seen universe is 48 billion light years. The universe is believed to be 13.5 billion years old. The universe started as a singular point. What gives? Is the expansion of the universe that much faster than the speed of light, or is there another explanation?[/quote]
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Jack_Ian
Posted: Mon Jan 08, 2007 5:02 pm    Post subject: 1

The universe need not have started as a single point. It is just that the observable universe, must have originally been in very close proximity.
We can currently observe objects receding from us at speeds faster than the speed of light. This does not mean that these objects are moving faster then the speed of light, but rather that space is expanding between us. Imagine an ant walking away from a dot on a balloon as it expands. If the ant is walking at 1 meter/minute, then due to the expansion of the balloon, after 1 minute the ant will be further than 1 meter away from its original position. The further something is away from us, the faster it recedes.
extro...*
Posted: Fri Jan 05, 2007 9:12 pm    Post subject: 0

Quote:
The age of the universe is about 13.7 billion years, and nothing travels faster than light; does it not follow that the radius of the observable universe must be 13.7 billion light-years? This reasoning might make sense if we lived in the flat spacetime of special relativity, but in the real universe, spacetime (not space!) is highly curved at cosmological scales, and light does not move rectilinearly. Distances obtained as the speed of light times a cosmological time interval have no direct physical significance.

I'm having a hard time wrapping my brain around "spacetime (not space!) is highly curved at cosmological scales". The notion of curved spacetime (but not space) ...
extro...*
Posted: Fri Jan 05, 2007 6:06 pm    Post subject: -1

btw, some related fascinating reading: http://www.lifesci.sussex.ac.uk/home/John_Gribbin/cosmo.htm
extro...*
Posted: Fri Jan 05, 2007 6:05 pm    Post subject: -2

Posted: Fri Jan 05, 2007 2:37 am    Post subject: -3

I think it has to do with thinking of the universe as 4 dimensional sphere, so that it's infinite but bounded. So, if every point on the original sphere expanded away from everything else by 13.8 billion light years or so, then what we can see would easily be 48 billion light years.
mudbuck
Posted: Thu Jan 04, 2007 4:37 pm    Post subject: -4

Or, the speed of light was faster in the good ol' days.
Antrax
Posted: Thu Jan 04, 2007 10:04 am    Post subject: -5

The radius of the seen universe is 48 billion light years.
The universe is believed to be 13.5 billion years old.
The universe started as a singular point.

What gives? Is the expansion of the universe that much faster than the speed of light, or is there another explanation?