In November of 1919, at the age of 40, Albert Einstein became an overnight celebrity, thanks to a solar eclipse. An experiment had confirmed that light rays from distant stars were deflected by the gravity of the sun in just the amount he had predicted in his theory of gravity, General Relativity. General Relativity was the first major new theory of gravity since Isaac Newton's, more than two hundred and fifty years earlier. Einstein became a hero, …showed first 75 words of 425 total…

…showed last 75 words of 425 total…clocks tick more slowly the closer they are to a gravitational mass like the sun. Many of the predictions of General Relativity, such as the bending of starlight by gravity and a tiny shift in the orbit of the planet Mercury, have been quantitatively confirmed by experiment. Two of the strangest predictions, impossible ever to completely confirm, are the existence of black holes and the effect of gravity on the universe as a whole (cosmology).