Olbers’ Paradox
  • Paradox attributed to Wilhelm Olbers, (1758–1840) who posed it in 1823 – but apparently also considered by Halley and perhaps earlier astronomers. Why is it dark at night? Or, more formally, why if the universe is infinite does the light from distant stars not add up to make the whole sky infinitely bright? The answer is in the size and age of the universe. There has not been enough time for light to get here from regions beyond the finite observable universe, and if it did it would be redshifted into invisibility by the expansion of the universe.

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