Year of the Comet
Comet C/2011 L4 (PANSTARRS)

PANSTARRS information

Comet C/2012 S1 (ISON)

ISON information

Ask Astro

Published: September 24, 2012
Cosmos
The biggest point of confusion in this question is the assumption that in 13.7 billion years the universe could have grown by only 13.7 billion light-years. This assumption is false. When we talk about the universe being a certain age, we mean that the proper time measured by a clock moving with cosmic expansion reads that many years since the Big Bang. If we use coordinates based on Albert Einstein’s special theory of relativity, that assumed clock moving with expansion travels close to the speed of light and thus hardly ticks at all. Thus, the universe can get huge before clocks have measured 13.7 billion years.

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