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March 15, 2018

Chris Adami: Remembering Stephen Hawking

March 15, 2018

Chris Adami is a professor in the Department of Physics and Astronomy, as well as professor of microbiology and molecular genetics. A theoretical physicist by training, he has spent more than two decades working on the quantum theory of information and its application to black holes.

The passing of the great physicist Stephen Hawking yesterday at the age of 76 fills me with sadness for many different reasons. On the one hand, it was inspiring to witness that, seemingly, the power of will and intellect can hold such a serious illness at bay for so long. On the other hand, I am also sad that I never got to talk to him, and perhaps explain to him my take on his great body of work.

Hawking's work has created arguably the biggest paradox in theoretical physics. While this seems daunting and perhaps concerning, it also has inspired hundreds — if not thousands — of physicists to work in the difficult area of quantum gravity, because the greatest rewards lie where the greatest problems are.

Beginning in 2003, I started to work on applying principles of quantum communication theory to the black hole problem funded by a generous grant from the Army Research Office. Over 10 years later, the first of a series of five articles on the black hole information paradox appeared, where I show how to use Einstein's theory of how light interacts with matter to calculate the rate at which black holes process information, within the formalism of curved-space quantum field theory developed by Hawking. This approach shows convincingly that black holes do not violate any laws, and (by amending Hawking's theory just a tiny bit) that theory can be appreciated in all its beauty.

Below, I share a brief anecdote involving Stephen Hawking and some of my physicist friends.

I ran into Stephen several times when I was at Caltech (which Hawking visited regularly), but a situation never developed in which we could "chat," as it were. One day in February of 1992 (see note at bottom), I was walking with Gerry Brown, a nuclear theorist who also visited Caltech each year in the spring, together with Hans Bethe, Brown's collaborator on the theory of binary neutron stars, along the lovely paths in Arcadia's Arboretum.

From afar, both Gerry and I spotted Hawking being pushed by his nurse along the path. Realizing that our paths would cross, Gerry and I both tried to get Hans to stop and engage Hawking, imagining that Hawking would be delighted to meet the eminent Bethe, winner of the Nobel Prize in Physics in 1967 for his discovery of how stars generate the energy to shine. However, Bethe curiously demurred. Later, I asked Gerry why Hans did not take this opportunity, and he answered: "You'd be surprised how shy Hans can be."

Hans passed away 13 years ago, Gerry left us almost eight years later and now Stephen is gone too. For me, it is always difficult to imagine that these great minds could simply cease to be. But after all, Hawking is known to have said, "I regard the brain as a computer, which will stop working when its components fail" and, in that, he was surely correct.

Of course, these great minds have left a legacy that is immortal, and we will keep them in our memory as long as we think about the stars, black holes and the vastness of the universe.

More detailed reflections about this period of time are published as "Three Weeks with Hans Bethe", in Hans Bethe and His Physics, edited by G.E. Brown and C-H. Lee, World Scientific (Singapore, 2006), pp. 45-110.