A paper just shy of two pages, published in the journal Nature on March 1, 1974, fundamentally altered the understanding of black holes, proposing they weren’t entirely “black” after all. The author, then a 32-year-old physicist at the University of Cambridge, was Stephen Hawking.
Prior to Hawking’s work, black holes were considered cosmic vacuum cleaners, relentlessly accumulating matter and growing in size, as dictated by Albert Einstein’s theory of relativity. Nothing, including light, was thought capable of escaping their gravitational pull. Hawking, however, began investigating the intersection of quantum mechanics – the physics governing the subatomic world – and black hole behavior.
Building on the earlier theoretical work of Jacob Bekenstein, Hawking combined general relativity, thermodynamics and quantum physics to arrive at a startling conclusion: black holes emit a faint radiation, now known as Hawking radiation. He posited that this radiation stemmed from the creation and annihilation of particle-antiparticle pairs near the event horizon, the boundary beyond which nothing can escape. Occasionally, one particle would fall into the black hole, while its partner escaped, carrying away a minuscule amount of energy.
As detailed in his 1988 popular science book, A Brief History of Time, this process leads to a gradual loss of mass for the black hole. While the evaporation of substantial black holes – those with the mass of the sun or greater – would accept far longer than the current age of the universe, Hawking theorized that primordial black holes, formed in the universe’s earliest moments, could have already exploded. “This is a fairly small explosion by astronomical standards but This proves equivalent to about 1 million 1 Mton hydrogen bombs,” Hawking wrote in his 1974 paper.
Hawking radiation quickly became a cornerstone of theoretical physics, but it simultaneously introduced a profound paradox. If information falls into a black hole and the black hole eventually evaporates, what happens to that information? The apparent loss of information violated a fundamental principle of quantum mechanics: the conservation of information. This became known as the black hole information paradox, and Hawking dedicated four decades to grappling with it, until his death in 2018.
In a 2015 lecture in Sweden, Hawking suggested that information might not be entirely lost, potentially escaping through wormholes – theoretical tunnels connecting different points in spacetime. “Black holes ain’t as black as they are painted. They are not the eternal prisons they were once thought,” he stated. “Things can get out of a black hole both on the outside and possibly come out in another universe.”
Following Hawking’s death, collaborators published papers proposing that information isn’t destroyed upon entering a black hole, but rather is eventually released. In 2024, physicists proposed a method for detecting this released information: subtle ripples in spacetime, observable as gravitational waves.
Despite these theoretical advancements, direct evidence of black hole explosions or primordial black holes remains elusive. However, recent observations by the James Webb Space Telescope have identified an ancient galaxy whose formation could potentially be explained by the presence of primordial black holes.
