|J. Robert Oppenheimer and Albert Einstein at the|
Institute for Advanced Study in Princeton
Forty years later when Einstein died, the implications of that paper had completely changed our view of the cosmos. They had explained the anomalous precession of Mercury, predicted the bending of starlight and most importantly, the expansion of the universe. Einstein enthusiastically accepted all these conclusions. One conclusion that he did not however accept and which in fact he did not seem interested in was the implications of the equations in areas of the cosmos where the force of gravity is so strong that it does not allow even light to escape - a black hole. Today we know that black holes showcase Einstein's general theory of relativity in all its incandescent glory. In addition black holes have become profound playgrounds for some of the deepest mysteries of the universe, including quantum mechanics, information theory and quantum gravity.
And yet Einstein seemed almost pathologically uninterested in them. He had heard about them from many of his colleagues; in particular his Princeton colleague John Wheeler had taken it upon himself to fully understand these strange objects. But Einstein stayed aloof. There was another one of the same persuasion whose office was only one floor away from him - J. Robert Oppenheimer, the architect of the atomic bomb and the Delphic director of the Institute for Advanced Study where Einstein worked. Oppenheimer in fact had been the first to mathematically describe these black holes in a seminal paper in 1939. Unfortunately Oppenheimer's paper was published on the same day that Hitler attacked Poland. In addition its importance was eclipsed by another article in the same issue of the journal Physical Review: an article by Niels Bohr and John Wheeler describing the mechanism of nuclear fission, a topic that would soon herald urgent and ominous portents for the fate of the world.
The more general phenomena of gravitational contraction and collapse that black holes exhibit were strangely phenomena that seemed doomed to obscurity; in a strange twist of fate, those who truly appreciated them stayed obscure, while those who were influential ignored them. Among the former were Subrahmanyan Chandrasekhar and Fritz Zwicky; among the latter were Oppenheimer, Einstein and Arthur Eddington. In 1935, Chandrasekhar had discovered a limiting formula for white dwarfs beyond which a white dwarf could no longer thwart its inward gravitational pull. He was roundly scolded by Eddington, one of the leading astronomers of his time, who stubbornly refused to believe that nature would behave in such a pathological manner. Knowing Eddington's influence in the international community of astronomers, Chandrasekhar wisely abandoned his pursuit until others validated it much later.
The Swiss-born Fritz Zwicky was a more pugnacious character, and in the 1930s he and his Caltech colleague Walter Baade published an account of what we now call a neutron star as a plausible explanation for the tremendous energy powering the luminous explosion of a supernova. Zwicky's prickly and slightly paranoid personality led to his distancing from other mainstream scientists and his neutron stars were taken seriously by only a few scientists, among them the famous Soviet physicist Lev Landau. It was building on Landau's work in 1938 and 1939 that Oppenheimer and his students published three landmark papers which pushed the envelope on neutron stars and asked what would be the logical, extreme conclusion of a star completely unable to support itself against its own gravity. In the 1939 paper in particular, Oppenheimer and his student Hartland Snyder presented several innovations, among them the difference between time as measured by an external observer outside a black hole's so-called event horizon and a free falling observer inside it.
Then World War 2 intervened. Einstein got busy signing letters to President Franklin Roosevelt warning him of Germany's efforts to acquire nuclear weapons while Oppenheimer got busy leading the Manhattan Project. When 1945 dawned both of them had forgotten about the key theoretical insights regarding black holes which they had produced before the war. It was a trio of exceptional scientists - Dennis Sciama in the UK, John Wheeler at Princeton and Yakov Zeldovich in the USSR - who got interested in black holes after the war and pioneered research into them.
What is strangest about the history of black holes is Einstein and Oppenheimer's utter indifference to their existence. What exactly happened? Oppenheimer’s lack of interest wasn’t just because he despised the free-thinking and eccentric Zwicky who had laid the foundations for the field through the discovery of black holes' parents - neutron stars. It wasn’t even because he achieved celebrity status after the war, became the most powerful scientist in the country and spent an inordinate amount of time consulting in Washington until his carefully orchestrated downfall in 1954. All these factors contributed, but the real reason was something else entirely – Oppenheimer simply wasn’t interested in black holes. Even after his downfall, when he had plenty of time to devote to physics, he never talked or wrote about them. He spent countless hours thinking about quantum field theory and particle physics, but not a minute thinking about black holes. The creator of black holes basically did not think they mattered.
Oppenheimer’s rejection of one of the most fascinating implications of modern physics and one of the most enigmatic objects in the universe - and one he sired - is documented well by Freeman Dyson who tried to initiate conversations about the topic with him. Every time Dyson brought it up Oppenheimer would change the subject, almost as if he had disowned his own scientific children.
The reason, as attested to by Dyson and others who knew him, was that in his last few decades Oppenheimer was stricken by a disease which I call “fundamentalitis”. Fundamentalitis is a serious condition that causes its victims to believe that the only thing worth thinking about is the deep nature of reality as manifested through the fundamental laws of physics.
As Dyson put it:
“Oppenheimer in his later years believed that the only problem worthy of the attention of a serious theoretical physicist was the discovery of the fundamental equations of physics. Einstein certainly felt the same way. To discover the right equations was all that mattered. Once you had discovered the right equations, then the study of particular solutions of the equations would be a routine exercise for second-rate physicists or graduate students.”
Thus for Oppenheimer, black holes, which were particular solutions of general relativity, were mundane; the general theory itself was the real deal. In addition they were anomalies, ugly exceptions which were best ignored rather than studied. As Dyson mentions, unfortunately Oppenheimer was not the only one affected by this condition. Einstein, who spent his last few years in a futile search for a grand unified theory, was another. Like Oppenheimer he was uninterested in black holes, but he also went a step further by not believing in quantum mechanics. Einstein’s fundamentalitis was quite pathological indeed.
History proved that both Oppenheimer and Einstein were deeply mistaken about black holes and fundamental laws. The greatest irony is not that black holes are very interesting, it is that in the last few decades the study of black holes has shed light on the very same fundamental laws that Einstein and Oppenheimer believed to be the only things worth studying. The disowned children have come back to haunt the ghosts of their parents.
As mentioned earlier, black holes took off after the war largely due to the efforts of a handful of scientists in the United States, the Soviet Union and England. But it was experimental developments which truly brought their study to the forefront. The new science of radio astronomy showed us that, far from being anomalies, black holes litter the landscape of the cosmos, including the center of the Milky Way. A decade after Oppenheimer’s death, the Israeli theorist Jacob Bekenstein proved a very deep relationship between thermodynamics and black hole physics. Stephen Hawking and Roger Penrose found out that black holes contain singularities; far from being ugly anomalies, black holes thus demonstrated Einstein’s general theory of relativity in all its glory. They also realized that a true understanding of singularities would involve the marriage of quantum mechanics and general relativity, a paradigm that’s as fundamental as any other in physics.
In perhaps the most exciting development in the field, Leonard Susskind, Hawking and others have found intimate connections between information theory and black holes, leading to the fascinating black hole firewall paradox that forges very deep connections between thermodynamics, quantum mechanics and general relativity. Black holes are even providing insights into computer science and computational complexity. The study of black holes is today as fundamental as the study of elementary particles in the 1950s.
Einstein and Oppenheimer could scarcely have imagined that this cornucopia of discoveries would come from an entity that they despised. But their wariness toward black holes is not only an example of missed opportunities or the fact that great minds can sometimes suffer from tunnel vision. I think the biggest lesson from the story of Oppenheimer and black holes is that what is considered ‘applied’ science can actually turn out to harbor deep fundamental mysteries. Both Oppenheimer and Einstein considered the study of black holes to be too applied, an examination of anomalies and specific solutions unworthy of thinkers thinking deep thoughts about the cosmos. But the delicious irony was that black holes in fact contained some of the deepest mysteries of the cosmos, forging unexpected connections between disparate disciplines and challenging the finest minds in the field. If only Oppenheimer and Einstein had been more open-minded.
The discovery of fundamental science in what is considered applied science is not unknown in the history of physics. For instance Max Planck was studying blackbody radiation, a relatively mundane and applied topic, but it was in blackbody radiation that the seeds of quantum theory were found. Similarly it was spectroscopy or the study of light emanating from atoms that led to the modern framework of quantum mechanics in the 1920s. Scores of similar examples abound in the history of physics; in a more recent case, it was studies in condensed matter physics that led physicist Philip Anderson to make significant contributions to symmetry breaking and the postulation of the existence of the Higgs boson. And in what is perhaps the most extreme example of an applied scientist making fundamental contributions, it was the investigation of cannons and heat engines by French engineer Sadi Carnot that led to a foundational law of science – the second law of thermodynamics.
Today many physicists are again engaged in a search for ultimate laws, with at least some of them thinking that these ultimate laws would be found within the framework of string theory. These physicists probably regard other parts of physics, and especially the applied ones, as unworthy of their great theoretical talents. For these physicists the story of Oppenheimer and black holes should serve as a cautionary tale. Nature is too clever to be constrained into narrow bins, and sometimes it is only by poking around in the most applied parts of science that one can see the gleam of fundamental principles.
As Einstein might have said had he known better, the distinction between the pure and the applied is often only a "stubbornly persistent illusion". It's an illusion that we must try hard to dispel.
This is a revised version of an old post which I wrote on occasion of the one-hundredth anniversary of the publication of Einstein's field equations.