Einstein's Monsters: The Life and Times of Black Holes

Every five minutes, a pair of black holes merges somewhere in the universe, pouring gravitational waves out into space.

Yet even Newton’s great intellect did not fully illuminate gravity. He couldn’t explain how it operates instantaneously and invisibly across a vacuum. He admitted as much in his masterwork on gravity from 1687, Philosophiae Naturalis Principia Mathematica. He wrote, “I have not been able to discover the causes of those properties of gravity from phenomena, and I frame no hypotheses.

Nature guards its secrets zealously, and it takes grit and determination to shed light on them.