Mass and Angular Momentum, Left Ambiguous by Einstein, Get Defined

In 1979, Nobel-prizewinning physicist Roger Penrose said that the two biggest unsolved problems in general relativity concerned mass and angular momentum (a measure of rotational motion). Both those properties, which are easy enough to understand in day-to-day life, spiral out of mathematical control when an object interacts with the curvy-wurvy effects of space-time within a finite region. Now both problems have been solved, thanks to a culmination of decades of work.