Professor Hawking, perhaps the world's most recognizable face of science, has died. Hawking's birth and death occurred on auspicious dates. March 14, the day he died, was the 139th anniversary of Albert Einstein's birth, and he was born on January 8,1942, the 300th anniversary of the death of renowned astronomer Galileo Galilei.
Hawking was diagnosed with amyotrophic lateral sclerosis, or ALS, a neurodegenerative disease that paralyzes the patient. When he received his diagnosis in 1963, doctors believed he had only two years to live. Defying all odds, he outlived that prediction by more than 50 years. And he put those 50 years to good use.
Hawking did not allow the paralysis of his body to cripple his nimble brain. Confined to a wheelchair, he spent his time in thought. While it would have been entirely understandable for him to sink into deep depression, instead he turned his mind to one of the thorniest problems of modern physics.
In 1915, Einstein invented the theory of general relativity, which describes the nature of gravity under extreme conditions. It predicts black holes -- places where gravity is so strong that not even light can escape. A few years later, a coterie of physicists invented quantum mechanics, a theoretical framework that explained the world of atoms and even smaller objects.
When researchers tried to combine these two subjects to understand the theory of gravity in the microcosm, they failed entirely. And that has been the state of affairs for the last century. Quantum gravity is still an unsolved problem.
Hawking's doctoral work showed Einstein's theory of general relativity predicted that the universe began in a singularity, which meant the energy and matter of the entire universe was concentrated in a single point. But he knew this result neglected the effects of quantum mechanics, which meant it was not the final word on the subject.
But it did point to the fact that studying black holes would be a fruitful way to learn about the birth of the universe. So, he spent the remainder of his scientific career investigating these cosmic conundrums.
His most influential work explored the nature of entropy in the vicinity of black holes. Entropy is a measure of disorder and there is a principle of physics that says that entropy (e.g. disorder) must increase. Yet matter falling into a black hole seemed to decrease disorder. Following a chain of thought proposed by a younger physics student by the name of Jacob Bekenstein, Hawking determined a relationship between the surface area of the outside of a black hole and the disorder.
Combining these insights led him to understand that black holes actually had a temperature. Since anything with a temperature radiates energy, this means that black holes radiate energy. This was impossible using just Einstein's equations, but when Hawking included the principles of quantum mechanics, he showed that black holes could indeed radiate energy. This energy is now called Hawking radiation. While it has not been experimentally confirmed, it is generally conceded to be true by working physicists.
Hawking's scientific work resulted in him being awarded the Lucasian Chair at the University of Cambridge, a position once held by Sir Isaac Newton. Hawking's scientific accomplishments are exemplary.
However, it is his contribution to society that made his greatest impact. Hawking was the most recognizable scientific face on the planet. His book "A Brief History of Time," written for nonscientists, has sold more than 10 million copies since its publication in 1988. He has appeared on "Star Trek: The Next Generation," "The Simpsons," and "The Big Bang Theory." He has published many other books with great success. It's been said that Hawking could publish his grocery list and it would be avidly read by his many fans.
If I might indulge in a personal anecdote: Hawking was one of many who inspired me to write my own books on science for the public (albeit with fewer copies sold). On one of his visits to Fermilab, we were able to speak very briefly. He had published "A Brief History of Time" and I congratulated him on its success and expressed an interest in writing myself. He encouraged me to try and the result was that several years later I published my first book. Several books later, I am still grateful for that encouragement.
Stephen Hawking influenced a generation of science enthusiasts for over three decades. Through his cordial relationship with the media, he motivated and inspired people to study the great questions and to think about the unsolved mysteries that stand before us. It is up to those of us who have followed in his footsteps to carry the torch and share his infectious enthusiasm for learning about the world around us.