Years ago, Stephen Hawking belittled the afterlife as a “fairy story for people afraid of the dark.” Now, if his unusual wish concerning his death is honoured, his gravestone will bear a mathematical formula instead of an uplifting epitaph: the equation for Hawking radiation, from one of the most elegant papers in the history of science. Published in 1974 in Nature, it had overturned traditional perceptions of the universe, for it predicted that black holes — which were seen as gravity wells from which nothing ever returned, not even light — actually bleed particles.
Small black holes could even explode like cosmic fireworks, and vanish in a gigantic puff of particles. That paper, simply titled “Black Hole Explosions?,” set physicists thinking afresh about quantum mechanics, which explains the universe on a very small scale — the world of subatomic particles — and gravity, which acts in the universe of large objects like the stars, or our own bodies.
Einstein had seen gravity as a wrinkle in the fabric of space-time caused by mass and energy but the Standard Model of physics does not account for the gravitational force. Four decades after Hawking’s paper appeared, it still provokes fresh thinking towards the Holy Grail of post-Newtonian physics — a theory of everything, absorbing gravity into the Standard Model, along with the electromagnetic force and the strong and weak interactions.
Hawking had stated his goal with staggering simplicity: “It is a complete understanding of the universe, why it is as it is, and why it exists at all.” The determination with which he pursued it, in the face of daunting physical odds, made him an inspirational figure. He may not have been the most original thinker in physics or mathematics — both the Nobel Prize for Physics and the Fields Medal have eluded him — but his reputation as a cosmologist is huge.
And his readiness to reach out to the general public made him a compelling evangelist of science, and of the scientific temper. Apart from writing several books for lay readers, starting with A Brief History of Time (it sold 10 million copies but was disparaged as “the most popular book never read”), he was a celebrity, appearing on television in Star Trek and Big Bang Theory. And he appeared in cameos in The Simpsons, whose scriptwriters have included math and physics nerds.
In the most memorable appearance, he is seen drinking in a bar with Homer Simpson, whose theory of a doughnut-shaped universe he threatens to steal. Homer responds: “I can’t believe that a guy I never heard of is hanging out with a guy like me.” The doughnut or “three-torus” model of the universe is real and was proposed in 1984 by researchers at Moscow’s Landau Institute.
The universe gave Hawking just one break after he was diagnosed with Lou Gehrig’s disease at the age of 21 and he took it. According to the prognosis, he had only a couple of years to live, but the motor neuron disease did not progress rapidly. His mind was unaffected and he retained the most important skill of a mathematician or cosmologist — the ability to hold very large logical arrays in the imagination. With the help of prosthetics and a wheelchair which he drove recklessly, he was able to put in over half a century of work. After his tracheostomy, his synthesised voice perhaps carried more force than the human voice, for it spoke of the power of the will.
Hawking has used that voice to intrigue and warn the public about the power of science. Most recently, he spoke out strongly for the regulation of artificial intelligence and the banning of autonomous weapons. AI, which will affect almost every aspect of culture, is being developed at breakneck speed, mostly behind the firewall of corporate secrecy. As Hawking had said in another context, “We only have to look at ourselves to see how intelligent life might develop into something we wouldn’t want to meet.”
The humour understated the real danger, of AI developing beyond human understanding and cognition. Hawking seriously feared that the world would come to a sticky end, whether by war, genetically engineered diseases, global warming or the rise of AI, and believed that going into space is the only credible way to spread risk. Indeed, despite his disability, he apparently had a ticket booked on Richard Branson’s Virgin Galactic. Hawking was also a vocal supporter of the multiverse, the set of realities encompassing the sum of space, time, matter and energy in the universe. The staple “parallel universes” of science fiction and popular culture, the idea has nevertheless echoed through the history of human thought, from the Bhagavad Gita to Schrodinger’s cat.
Until he retired in 2009, Hawking held the Lucasian Chair of Mathematics at Cambridge University. His predecessors have included computing pioneer Charles Babbage, quantum mechanics co-founder Paul Dirac, who predicted the existence of antimatter, and Isaac Newton, who first explained gravity, the force which features in Hawking’s most important work. It is entirely fitting for his epitaph to be the mathematical formula for Hawking radiation. Now, they only have to find an artist who can engrave a headstone with Boltzmann’s constant, Planck’s constant, Newton’s gravitational constant and pi. And with feeling.