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In John Gribbin's Ten Tantalizing Truths, the author discusses the puzzle of dark night sky:-

The person who first expressed the puzzle clearly in scientific terms was the Swiss astronomer Jean-Philippe Loys de Chéseaux, in the 1740s. The big difference between his approach and earlier speculations was that he put real numbers into the calculation. He estimated the distances to stars by guessing that they were all the same actual brightness as the Sun and working out how far away they would have to be to look so faint. Then he worked out how big the disc of the Sun would look to us at those distances. Finally, he worked out that if stars were spread out more or less evenly through the Universe in the same density as they are in our part of the Universe, these discs would all be overlapping, so the entire sky would be as bright as the Sun, once we looked out to a distance equivalent, in modern terms, to 1015 (a million billion) light years. His conclusion was that either stars are not distributed evenly in this way – that there must be an ‘edge’ to our grove of astronomical trees – or that something happens to hide the light from very distant stars. De Chéseaux suggested that light gets fainter and fainter as it travels across space to us. He was wrong (or at least, partially wrong, as I shall explain), but at least he tried to explain the puzzle.

I can't get the connection between these two sentences! what's the connection between the stars being not evenly distributed and the universe being finite?

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  • $\begingroup$ Which two sentences? The text does not mention the finiteness of the universe. $\endgroup$
    – ProfRob
    Jun 25, 2023 at 6:09
  • $\begingroup$ @ProfRob These two "His conclusion was that either stars are not distributed evenly in this way – that there must be an ‘edge’ to our grove of astronomical trees". He indicates the finiteness of universe by saying "there must be an ‘edge’ to our grove of astronomical trees" $\endgroup$ Jun 25, 2023 at 6:23
  • $\begingroup$ This is Olber's Paradox - en.wikipedia.org/wiki/Olbers'_paradox $\endgroup$ Jun 26, 2023 at 18:12

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The highlighted text is part of one sentence and expresses one idea - that the darkness of the night sky might be explained if the stars were distributed uniformly out to some finite distance. That is not an even distribution throughout the whole universe, since there is not necessarily any connection between the size of the universe and the volume occupied by stars.

i.e. We could be sitting in an island of stars surrounded by an infinite universe containing no stars. What appears to be being ruled out is an infinite universe that contains stars everywhere. Note though that the possibility of a finite age of the universe plus a finite speed of light was not considered.

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  • $\begingroup$ Then the second "that" isn't necessarily explanatory? $\endgroup$ Jun 25, 2023 at 6:38

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