Great Papers #10: The Expanding Universe, Hubble 1929

How big is the universe, and does it change? In the 1920s nobody knew. This episode reads Edwin Hubble's 1929 paper, which answered both. Using Cepheid standard candles (Henrietta Leavitt's law) and the 100-inch telescope on Mount Wilson, Hubble first showed the spiral "nebulae" are separate galaxies — the universe is vastly bigger than the Milky Way. Then he plotted galaxy distances against their redshifts and found a straight line: the farther a galaxy, the faster it recedes. That's the signature of an expanding universe — space itself stretching, no center and no edge. And it loops straight back to this batch's opener: Einstein's equations had predicted exactly this, and he'd fudged them to stop it (his "greatest blunder"). Run the movie backward and you get the Big Bang; run it forward and, since 1998, the expansion is accelerating — dark energy, the deepest mystery in cosmology. Closes Great Papers Batch 2. ——— Series: Great Papers · UnderGrad level. Every equation spoken in full, no chalkboard required. Built by Fermi AI.