“Black hole.” “Wormhole.” These are terms familiar to any English speaker if not from science fiction literature and films, then at least from pinball machines and arcade games. For a generation raised on Star Wars they have become all too familiar, yet they have not been around for very long. Both the two terms and the theory behind them were coined by one man – the late Princeton Professor Emeritus John Wheeler – in the late 1950s and 60s.
Dr. Wheeler passed away the Sunday before last, April 13th, at his home in Hightstown, NJ, leaving behind a remarkable legacy. At 96, the list of his achievements read like something that could reasonably have been accomplished in several lifetimes.
An entirely self-made man, Wheeler came from a humble background. Born in Jacksonville, Florida on July 9, 1911 to a homemaker and a librarian, Wheeler slowly taught himself the sciences from library books his father brought home with him. These books inspired him to “tinker” and he spent his childhood constructing a wide array of gadgets. This tinkering eventually sent him on scholarship to Johns Hopkins at the age of 16. At 21 he was conferred a doctoral degree in physics and went off to begin his research under the guidance of Niels Bohr in Denmark.
From this point on, Wheeler’s life appears as a whirlpool of conversations with Bohr and Albert Einstein, photographs strolling through the park with Enrico Fermi and Richard Feynman. One discovery seems to follow on another, manifest in a growing collection of Wheeler-isms. (Of these, three would later give rise to the title of his autobiography: “Geons, Black Holes, and Quantum Foam: A Life in Physics.”) More than a mere theorist, however, Wheeler never left plain, palpable reality too far behind him.
His initial discoveries in nuclear physics were almost immediately put to practice in the Manhattan Project, and later in Project Matterhorn. Wheeler’s first major discovery, the Scattering Matrix (or S-Matrix, as it is widely known) is still used by scientists today to describe particle interaction. His next major enterprise followed in 1939 when his former mentor, Niels Bohr arrived on American soil with the ill tidings of nuclear fission. That same year Bohr and Wheeler proposed the famous “liquid drop model” of nuclear fission, whereby the atomic nucleus is imagined as a drop of incompressible, nuclear liquid. In this model, one disintegrating nucleus emits a neutron which hits another such nucleus. This causes the latter nucleus, a “liquid drop,” to begin vibrating until it stretches into a peanut shape and finally splits in two. This model eventually led to the creation of a mathematical formula able to predict the binding energy of such a nucleus and was instrumental in the creation of the atomic bomb.
Wheeler became involved with the Manhattan Project in 1941, working at its Hanford site which produced the necessary plutonium. His foresight allowed Wheeler to predict the accretion of “fission product poisons” – special isotopes such as Xe135 that would eventually absorb the neutrons responsible for perpetuating the nuclear chain reaction. The Project was thus adjusted accordingly, and its result is well-known.
At the end of the war Wheeler leapt into Project Matterhorn where he worked for some time on the hydrogen bomb and became a mentor to the young Richard Feynman. Feynman, however, was just one of Wheeler’s many students who went on to lead influential careers. After concluding his work on Project Matterhorn, Wheeler returned to lecturing at Princeton, where he had been officially hired in 1938. The end of the war signaled a new era for Wheeler, one in which he would be at his most inspired. In his autobiography, Wheeler confessed that it was not until he began working with general relativity and gravitation at this time that he “finally had a calling.”
“I think he felt that nuclear physics got to a stage by the mid-fifties where the big questions were answered and there was no longer much to do. There was still a lot of important research to be done but it wasn’t at the forefront anymore,” said Professor Strauss of Princeton’s Astrophysics department.
Working at Princeton, it seems natural now that Wheeler picked up where his predecessor, Albert Einstein left off. At the time, however, this was far from an expected or foreseeable move. “Everyone was convinced that general relativity was right but didn’t know what to do with it,” Professor Strauss explained. “General Relativity looks like Newtonian gravity in most situations. No one yet knew of astrophysical situations in which general relativity becomes important – people did not yet know about neutron stars or black holes.
So it was not considered a fruitful area to work in. It wasn’t considered ‘not legitimate’, but it was a dormant field. Therefore, it was a rather bold move for Johnny Wheeler and a rather prescient one because in the 1960s, at least partly spurred on by his work, there were a number of discoveries in astronomy that absolutely required general relativity.”
Again, Wheeler’s foresight paid off. It was during this second stage of his life that he developed the concepts of the ‘wormhole,’ a potential tunnel in space-time, and the ‘black hole,’ a collapsed star. The initial idea of the ‘black hole’ was first proposed by J.Robert Oppenheimer and one of his students, Hartland Snyder, as a natural extension of Einstein’s theory. Wheeler invented the term, however, at a conference in 1967, and has been associated with it ever since.
The story of how a black hole originates goes something like this:
A star is made up primarily of hydrogen and helium, which are exhausted over time in the process of fusion – that is to say they serve as the star’s “fuel.” (The more massive a star, the faster it burns up this fuel.) After devouring all its hydrogen, the star begins consuming helium. This reaction produces lithium, which the star also consumes in a reaction that generates an even heavier element. This process continues until iron is the ‘heavier element’ generated by the reaction. This is the heaviest (and last) element in the chain that a star can efficiently manufacture. Everything heavier than iron is created only in miniscule quantities.
It is at this point, when the star has essentially run out of fuel, that some major changes take place. Small stars slowly cool off and “die,” becoming, what is termed in the astrophysics community, “cold, dark, dwarf stars.” Massive stars, on the other hand, have a much more glorious fate: they explode in colorful supernovas. It is these latter stars that, Oppenheimer and Snyder predicted, when of sufficient size, will continue perpetually collapsing unto themselves, creating the dark region of space known as a ‘black hole.’ These ‘holes,’ they hypothesized, would continually consume the space around them (everything beyond a circular parameter known as the black hole’s ‘event horizon,’) dragging it into the center of infinitely curved space and infinitely dense matter.
Although the idea stemmed from Oppenheimer and Snyder, Wheeler is best remembered for his extensive investigation into the phenomenon. Considered only a hypothetical possibility at the time, the existence of black holes has since been confirmed by observable phenomena. Even the center of the Milky Way is now known to be a 2.4 million solar mass black hole.
Although he spent a considerable amount of time pondering the physics of black holes and quantum gravity, Wheeler never lost sight of what he considered to be his most important charge – his students. Wheeler taught introductory physics until his retirement from Princeton in 1976. He is remembered by many of his colleagues as well as students, as an exceptional teacher and advisor, whose own work often provided the basis on which his more advanced students built their careers.
“He had many famous students including Richard Feynman, Kip Thorne, and Jacob Bekenstein,” Professor John R. Gott also of Princeton’s Astrophysics department said. “He told Bekenstein to think about entropy in connection with black holes. This investigation eventually led Stephen Hawking to his most famous result–that black holes emit thermal radiation. Wheeler’s idea that positrons could be considered to be electrons moving backward in time was used by Richard Feynman in his Nobel Prize winning work on Quantum Electrodynamics. Wheeler was a great lecturer, filling the blackboard with drawings and ideas. He will be missed.”
Despite the success of his students however, Wheeler himself was never awarded a Nobel Prize. Simply put, his discoveries in general relativity were not empirically provable, and the Nobel committee does not like to take any chances, however slight.
“There are a number of things he did which came close to being appropriate for a Nobel,” Professor Strauss said. “If you read his autobiography, in at least two places, he mentions work he did and never published, that later others ended up repeating and winning the Nobel Prize for. I think this was for work in nuclear physics, not general relativity.”
Those who knew him at Princeton, however, don’t believe this bothered him at all. A self-professed naïve optimist, Wheeler is remembered for always being able to look on the bright side. A man who saw the world in all its flux, who was highly aware of all the variable and unknowns, he never let his spirit of the constancy of his beliefs be swayed. He was a man who dared to imagine human beings as the constant creators of the universe, and who never gave up on the dream of a unified field theory, capable of encompassing all physical phenomena.
“We are no longer satisfied with insights only into particles, or fields of force, or geometry, or even space and time,” the New York Times obituary cites Wheeler as having written in 1981. “Today we demand of physics some understanding of existence itself.”
Dr. Wheeler’s body was laid to rest in a familial burial plot in Benson,Vermont. I’d somehow like to think, though, that he is somewhere on the other side of a black hole, looking through at our universe and laughing as he sees it all come together.