General Relativity

In November of 1915, members of the Prussian Academy of Sciences in Berlin watched the universe change. Over four consecutive Thursdays, Albert Einstein presented lectures on his new theory of gravity. The last, on November 25th, offered the detailed mathematics that explained it all — the field equations in support of the general theory of relativity.
At the time, the leading theory was that of Isaac Newton, which said that gravity was a “force” that attracted objects to each other.
Einstein, though, said that gravity was a warp in space-time caused by matter. The greater an object’s mass, the more it warped the space around it. The difference in Newton’s and Einstein’s gravity isn’t that important for many applications, such as sending spacecraft to other planets. But it is important in many places, such as especially strong gravitational fields.
Einstein had been pursuing general relativity for years. He was trying to reconcile it with his earlier theory of motion, special relat