  This year marks the 100th anniversary of Einstein's General Theory of
Relativity (1915-2015). The first nontrivial solution of the Einstein field
equations was derived by Karl Schwarzschild in 1916. This Note will focus
mainly on the Schwarzschild solution and the remarkable developments which it
inspired, the most dramatic being the prediction of black holes. Later
extensions of Schwarzschild's spacetime structure has led to even wilder
conjectures, such as white holes and passages to other universes. Penrose
diagrams are introduced as compact representations of extended spacetime
structures. Stephen Hawking's derivations of quantum effects in black holes
might provide clues to an eventual "Theory of Everything" encompassing both
general relativity and quantum mechanics.
