If the universe was finite, and had a size of about 4 billion to 5 billion light-years, then light would be able to wrap around the universe, and with a big enough telescope we could view the Earth just after it solidified and when the first life formed. Unfortunately, our results rule out this tantalizing possibility.

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Several years ago we showed that any finite universe in which light had time to 'wrap around' since the Big Bang would have the same pattern of cosmic microwave background temperature fluctuations around pairs of circles.

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It can be thought of as a spherical diameter is the usual sense.

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