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How many light years across is the universe?

Answer 1

The observable universe is about #93# billion light years across.

The age of the universe is about #13.8# billion years. So the earliest light we see is from roughly that time. Since nothing travels faster than light, you might think that means that the universe is about #2xx13.8# billion #= 27.6# billion light years across. But the universe has been expanding for the last #13.8# billion years. So the oldest light we see is from places that are now much farther from Earth than #13.8# billion light years.

There is a subtle difference between the visible universe and the observable universe, in that the universe only started to shine about #378,000# years after the Big Bang. So the observable universe is slightly larger (#93# Gly) than the visible one (#91.4# Gly).

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Answer 2

Luca de

The diameter of the observable universe is estimated to be 93 billion light-years.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.