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Notes and Reflections on Books and Media

by Hannah Leitheiser

Book

Sidelights on Relativity

Einstein

1921

2016-12-11

"Assuming that we know, let us say, the statistical distribution of the stars in the Milky Way, as well as their masses, then by Newton’s law we can calculate the gravitational field and the mean velocities which the stars must have, so that the Milky Way should not collapse under the mutual attraction of its stars, but should maintain its actual extent. Now if the actual velocities of the stars, which can, of course, be measured, were smaller than the calculated velocities, we should have a proof that the actual attractions at great distances are smaller than by Newton’s law. From such a deviation it could be proved indirectly that the universe is finite. It would even be possible to estimate its spatial magnitude." -- Sidelights on Relativity, Einstein, 1921

Of course, now this work has been done and a discrepancy found but in the other direction. Einstein, if I understand correctly, is arguing here for lower speed pointing to a finite cosmological topology and it's a bit beyond me to see the mathematics of it, but what does it mean if larger?