At the time of writing, the news of the death of Stephen Hawking CH CBE FRS FRSA has reverberated around the world. Widely regarded as the greatest cosmologist of all time, Hawking was the Director of Research at the Centre for Theoretical Cosmology at the University of Cambridge when he died on the 14th of March 2018, at the age of 76.
One of Hawking’s most famous quotes states that regardless of one’s personal circumstances, there is always something one can do, and in this case, Hawking had done much to improve our knowledge and understanding of some of the most vexing and intractable problems and questions in astronomy and cosmology. Therefore, Hawking should not be remembered for his death from a form of Lou Gehrig’s disease, but rather for his long list of accomplishments, almost all of which were achieved while he was immobile, and bound to a wheelchair.
Nevertheless, who was Stephen Hawking? One way to answer this would be to list all of his research papers (and their scope) in a large volume, and perhaps to mention that he had tutored 40 doctoral students. However, this hardly does full justice to his towering intellect, which was not always immediately apparent from his general published works that includes the best seller “A Brief History of Time”, of which nine million copies were sold.
In fact, most of Hawking’s work was done “behind the scenes”, in the sense that amateur astronomers were not always aware of just how profoundly his discoveries and insights into the nature and structure of the Universe was responsible for changing the way new generations of scientists were seeing the Universe they thought they knew. There are many examples of this, but from the perspective of amateur astronomers, the best-known example is perhaps the fact that Hawking had not only “discovered” black holes in the sense that he proved their existence, but had also described both their nature and effects on their immediate surroundings.
At this point, it is perhaps fitting to quote Albert Einstein, who once said; “If you cannot explain a complex matter in simple terms, you do not understand it well enough.” This most certainly did not apply to Hawking and his understanding of black holes. In fact, Hawking used both prior knowledge and his own insights into the matter to develop the now-famous Hawking Equation, which not only describes black holes, but which also showed that black holes emit a form of radiation, which now bears his name. The equation is shown below:
In this equation, “S” represents the amount of entropy (disorder) that is present in the system (black hole). The “S” is sometimes written with “BH” superscripted, to acknowledge to role of Jacob Bekenstein, who also did much to unravel the mysteries of black holes.
Nonetheless, the “h” represents the Planck Constant, the “G” represents Newton’s Constant, which defines the role of gravity; the “A” represents the area of the event horizon that surrounds the black hole, the “c” represents the speed of light in a vacuum, and the “k” represents Boltzmann’s Constant, which defines how energy relates to temperature. While the nuts and bolts of this equation is above most amateur astronomers, it nevertheless contains the essence of Hawking’s work. Furthermore, the equation is also an elegant expression of the notion that would later define his life and work, that being that black holes were not entirely black after all, and instead emitted a glow that would come to bear his name.
With reference to Einstein’s quote that one must fully understand a difficult subject before one can explain that topic in simple terms, Hawking explained his equation and hence, the nature of black holes in exceedingly simple terms during his 60th birthday celebrations thus:
“In particular, I wondered, can one have atoms in which the nucleus is a tiny primordial black hole, formed in the early universe? To answer this, I studied how quantum fields would scatter off a black hole. I was expecting that part of an incident wave would be absorbed, and the remainder scattered. But to my great surprise, I found there seemed to be emission from the black hole. At first, I thought this must be a mistake in my calculation. But what persuaded me that it was real, was that the emission was exactly what was required to identify the area of the horizon with the entropy of a black hole.”
By all accounts, Hawking was a humble man, but all the same he recognized his Equation as both his greatest achievement, and a momentous advance in the science of cosmology, which is perhaps the best measure of the man. However, Stephen Hawking, the scientist, is perhaps best described by his request that “I would like this simple formula to be on my tombstone.”
May Stephen Hawking be remembered for long after the equation that is engraved upon his tombstone has worn away.