7) Two hundred years ago most philosophers thought that our universe was infinit

Question

7) Two hundred years ago most philosophers thought that our universe was infinitely old and infinitely big. In 1823, Heinrich Olbers pointed out these assumptions are disproved by a simple observation of the night sky. What observation was this?

8) What is the evidence we have that dark matter exists within individual galaxies? In other words, exactly what observations do we make with our telescopes which tell us that there is dark matter inside individual galaxies?

9) What are the three types of evidence we have that there is dark matter in clusters of galaxies?

Explanation / Answer

7)

The observation was the darkness of the night sky. If our universe was infinitely old and infinitely big, then any line of sight from the Earth must end at the surfacce of a star(which is very bright) and hence the night sky should be completely illuminated and very bright. This contradicts the darkness and non-uniformity of the night. This observation is termed as Olbers' Paradox.

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