This week, the universe lost physicist Stephen Hawking at the age of 76. To be fair, that’s several decades after we should have lost him; at 21, he was diagnosed with amyotrophic lateral sclerosis, and was expected to only live a few more years. Fortunately for the world of physics, Hawking’s body limped along just well enough to let his brain survive and flourish, providing the scientific community with new insights into one of the most bizarre phenomena in the universe: black holes.
The concept of an object having a gravitational force so massive that not even light could escape dates back to the late 1700s, but the theory hit a snag when it was determined that light was a wave (it’s also a particle, but that’s for another discussion). People at the time thought that a force could not possibly act on a wave, and the idea was shelved for over a century. Einstein’s theory of relativity in the early 1900s, however, provided a new model for explaining gravity. It was not a force, it was the effect of mass bending space-time itself, and that light would travel through that bend in space. If the bend was “steep” enough, due to an extremely massive object, the light could not overcome its pull. The term “black hole” was first published by Ann Ewing in 1964, but because the world is the way it is, the term didn’t catch on until John Wheeler used it 3 years later (happy belated International Women’s Day!).
According to general relativity, the center of a black hole contains a singularity, which is infinitely dense. Hawking’s first major contribution to understanding black holes was comparing the process to the Big Bang. The process by which matter condensed into the singularity of a black hole, to Hawking’s eyes, mirrored the expansion of the Big Bang, and he published this proposal with Roger Penrose in 1970. He also proposed that black holes could only increase in mass, as matter can enter the event horizon (the point at which the gravity overcomes all other forces), but cannot escape.
Two years later, Jacob Bekenstein determined that the black holes contribute to the increasing entropy of the universe. If they followed the second law of thermodynamics, however, this would require black holes to have a temperature, which would mean that they would emit radiation. But no radiation (such as light, remember?) can escape a black hole. If this doesn’t make sense to you, then congratulations, you’ve been paying attention. Hawking proposed a mechanism for this radiation, which is that paired quantum particles are split apart at the edge of the event horizon, releasing radiation. And as he officially got dibs, we now call this “Hawking Radiation.”
The next proposal from Hawking regarding black holes regarded the information contained in the waves and particles that passed the event horizon, such as their position or mass; Hawking postulated that the information was destroyed. This was not universally accepted, and John Preskill countered that the information could be emitted in the Hawking Radiation. In 2004, Hawking conceded defeat; there was sufficent argument that information remained in some form. In his usual playful fashion, he awarded Preskill the encyclopedia they had bet on the outcome.
This lost wager encapsulates three of Hawking’s important traits: he wasn’t always right; he wasn’t afraid to take a big swing and look as hard as he could to find evidence for or against it; and he maintained a playful joy of discovery. He loved to share this exuberance, in his books, lectures, and even his television appearances. Those of us that were not lucky enough to meet him in life will certainly have the chance in Atheist Heaven.
Wait… hmmm. Crap.