A "Whodunit" of Cosmic Proportions

In a few months I'll be teaching my high-school students about cosmology and, in particular, how Edwin Hubble discovered that the universe is expanding. That's how most of us learned it, anyway, but it's not the whole story. In fact, it's not even correct.

During the 1920s, astronomers Edwin Hubble (left) and Georges Lemaître both came o the realization that the universe is expanding.

Carnegie Inst. of Washington / Catholic Univ. Louvain Hubble came to his game-changing revelation when he compared his distance measurements of a few dozen galaxies (or "spiral nebulae," as they were then called) with prior observations by astronomer Vesto Slipher, who'd analyzed their spectra and found they were racing away from us at various speeds. In 1929 Hubble published "A Relation between Distance and Radial Velocity Among Extra-Galactic Nebulae" — not mentioning Slipher at all, by the way — and forever transformed how we view our universe

I like the story of Einstein's wife, on a visit to Mount Wilson, being told that scientists there were making measurements that could determine the size of the Universe. "Oh, my husband can do that on the back of an evelope!", she replied. I don't think she meant it ironically, either.

Oh Yeah? And how is he going to get the evelope to sit still while he carries out his calculations?

The irony is in the fact that when Einstein first published his theory of General Relativity, the known universe contained only the Milky Way galaxy. In order to account for this “fact” he included a fudge factor, Einstein’s cosmological constant. He later called it the biggest blunder of his scientific career.

Andromeda and other Galaxies were thought at the time to be near-by star clusters or gas clouds. Using variable Cephids, Hubble was the first to demonstrate that the Andromeda nebula must be at least a million light years away, and therefore enormous, consisting of billions, if not trillions, of individual stars. He later made a systematic study of galaxies and redshifts, using the variable Cephid trick and made very accurate estimates of recession velocity and distance, far better and more reliable, than Abbot Lemaître’s. Lemaître will forever be remembered as one of the first physicists (along with Eddington) to successfully challenge Einstein’s cosmological constant.

Click the Pic Thank you, JoeProBono

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