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Astrophysicist Estimates Diameter Of The Universe
The diameter of the Universe has been estimated at 156 billion light years by astrophysicist Neil Cornish (Montanna State University). The results were published in Physical Review Letters last week.
The estimate was reached by estimating both the time that light has been traveling from the most distant galaxies we can see, and then factoring in the expansion of the space in between galaxies that has happened since the Big Bang.
How can the most distant galaxies be both 13.7 billion years old, and yet 156 billion light-years apart? Did they travel faster than light? Space.com asked Neil Cornish:
"The problem is that funny things happen in general relativity which appear to violate special relativity (nothing traveling faster than the speed of light and all that).
"Let's go back to Hubble's observation that distant galaxies appear to be moving away from us, and the more distant the galaxy, the faster it appears to move away. The constant of proportionality in that relationship is known as Hubble's constant.
"One seemingly paradoxical consequence of Hubble's observation is that galaxies sufficiently far away will be receding from us at a velocity faster than the speed of light. This distance is called the Hubble radius, and is commonly referred to as the horizon in analogy with a black hole horizon.
"In terms of special relativity, Hubble's law appears to be a paradox. But in general relativity we interpret the apparent recession as being due to space expanding (the old raisins in a rising fruit loaf analogy). The galaxies themselves are not moving through space (at least not very much), but the space itself is growing so they appear to be moving apart. There is nothing in special or general relativity to prevent this apparent velocity from exceeding the speed of light. No faster-than-light signals can be sent via this mechanism, and it does not lead to any paradoxes."
For more information, see Universe Measured: We're 156 Billion Light-Years Wide!; reference from KurzweilAI.net.
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