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Originally Posted by stuart Yep, pretty much what Dragon Star said. But, you can define the visible universe which is the universe that we have any hope of ever seeing due to the finite age of the universe and finite speed of light. If just going by these, then our "horizon" is a sphere about 13 billion light-years in radius, which is as far as we can see because light from farther places hasn't had enough time to reach us. But, we can only see back to about 300,000 years, due to the Cosmic Microwave Background radiation, so the sphere is [however old the universe is]-300,000 light-years in radius. A good website explaining the CMB radiation is http://map.gsfc.nasa.gov/ . |
Just a point to poke out there....
Problem with the light theory of Universal size is due to the expanding space/time, the speed of light was once much faster then it is today, meaning that the visible universe is much more vast then previously thought. And it is difficult to judge just how much light has slown down from BB, it could be as much as a few billion years...