In so doing, he touched on a persistent headache for physicists: Einstein’s theory, which has withstood every experimental test so far, does not explain the behaviour of particles in the subatomic, “quantum” sphere.
Considered controversial at first, Hawking’s black hole theory pointed to a possible bridge between the two mainstay physics theories – general relativity and quantum mechanics.
“Hawking realised that black holes, these objects that are made of gravity, because of quantum mechanics... can actually emit particles,” said astrophysicist Patrick Sutton of Cardiff University. “This was the first case where we had a physical process that links gravity, this classical theory of gravity, with quantum mechanics.”
The mechanism was named “Hawking radiation” after the famous scientist who died Wednesday – on Einstein’s birthday. And it painted a completely new portrait of black holes.
“Stephen Hawking discovered that when the quantum laws governing the physics of atoms and elementary particles were applied to black holes, the surprising outcome was that black holes actually must emit radiation,” physicist Raymond Volkas of the University of Melbourne said via the Australian Science Media Centre.
Hawking showed that because black holes give off radiation they actually have a temperature. And in losing mass and energy, they would slowly shrink and eventually evaporate – “a real shock” proposition, according to Sutton.
“Hawking’s most important scientific legacy is his idea that black holes slowly dissolve like aspirin in a glass of water,” said Lisa Harvey-Smith of the University of New South Wales.
But Hawking radiation in turn posed a new problem, the so-called “black hole information paradox.”
If a black hole disappears, all the cosmological information from matter and energy that initially went into it will disappear too. But physics predicts that information can never be lost. Hawking himself had conceded a wager on the point, having initially bet that black hole information will ultimately be lost.
Besides his deep imprints on theoretical physics, many credit Hawking’s popularisation of science, including through his cosmology-themed book A Brief History of Time, with motivating their own interest and careers.
“His impact on the public understanding of science is almost beyond measure,” said Harvey-Smith.