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The Question

(Submitted March 28, 1997)

I understand that the cosmic particle horizon is located about 20 billion light years away, in all directions, from me. Light coming from objects located past the horizon cannot be seen because the light has not had enough time to reach me yet. But doesn't the cosmic particle horizon expand with the expansion of the Universe. Therefore, light that I couldn't see before can be seen in the future. Is this conclusion sound?

The Answer

The cosmic particle horizon is related to the age of the Universe. Its size certainly grows, but with the age of the Universe, not with the expansion of the Universe. As the expansion slows, we certainly would see more in the future than in the past. But, of course, the time scales for this to happen are very large.

Jim Lochner
for Imagine the Universe!

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