Credit: NASA
Many of you have woken to the sad news of the passing of Stephen Hawking -- a towering figure in theoretical physics and cosmology, who inspired so many within science and beyond, with his intellectual insights into the nature of the universe, his wit, and his zest for the life that doctors once told him he would never have.
It's difficult to overstate Hawking's influence on the physics community. Roger Penrose, writing in the Guardian, and Martin Rees, in Nature, have written extremely accessible descriptions of the impact of his work. In the 1960s, with Penrose, George Ellis, and others, Hawking's calculations helped to elucidate the mathematics of how the big bang marks the beginning of not just space, but time itself, from an infinitely small, dense "singularity." Such singularities represent the breakdown of our best theories of physics and are also thought to lie at the heart of black holes, shrouded by an event horizon. It was believed that these event horizons act as one-way membranes that allow nothing that passes, not even light, to escape a black hole's clutches. But, in the 1970s, Hawking's work examining black holes with both general relativity and quantum theory, led him to propose that black holes can, in fact, slowly radiate particles, through the process of what has become known as "Hawking radiation." This, in turn, suggests that black holes will slowly evaporate away -- raising profound puzzles over the fate of information about the objects that fell in to the black hole.
This black-hole information paradox has yet to be resolved to everyone's satisfaction; in fact, in recent years it has only become more confounding. But, as is often the way in science, posing questions can sometimes be as fruitful as offering solutions -- and researchers are using this paradox, and its offshoots, as a handle to try to understand which of the two cornerstones of physics, Einstein's general theory of relativity or quantum theory, has to give. Many FQXi members are today absorbed in projects that have their roots in Hawking's work.
But Hawking's influence goes deeper. As the bestselling author of A Brief History of Time, he directly inspired so many of us to study physics and cosmology, in the first place. I've lost count of the number of FQXi members who cite reading the book as a defining moment in their lives. I myself read natural sciences at Cambridge University, where Hawking was based and held the Lucasian Chair of Mathematics for many years. My fellow students and I never ceased to be excited to hear Hawking, or bump into him on the streets (quite literally, in the case of a friend, whom I recall returning to college one afternoon in a flustered state because she had cycled into his wheelchair). And while there might have been a danger that his celebrity status would give him an aura of unapproachability, he undercut this with his humour and the twinkle in his eyes. Hawking laced his public talks with jokes, managing to display comic timing despite speaking through a voice synthesiser. I personally loved him playfully claiming that the Spice Girls were his favourite group, for instance (or possibly that was entirely sincere, I'm not sure).
Later, as a science journalist, I was honoured that Hawking agreed to be interviewed by me for New Scientist and Nature, both about his own work, and to give his thoughts on that of others, even though providing comments clearly took a physical toll. But, of course, in addition to his scientific accomplishments, he will be remembered and admired for his commitment to engage the public and his refusal to be defined by the motor-neurone disease that struck him at just 21 years of age. That legacy will remain for generations to come.
Our thoughts at FQXi are with Hawking's family, friends, and colleagues.