| “We are not only observers. We are participators. In some strange sense this is a participatory universe.” |
John Archibald Wheeler
One Year has been passed. On April 13, 2008, John Archibald Wheeler, the doyen of Modern Physics passed away at the age of 96. When I heard the news that Wheeler is no more, I had strange feeling. A feeling of losing a dear and nearer one forever.
I have not seen him. I am not fortunate enough to hear his lectures. But his books, essays and compliments showered on him by his students and colleagues created deep impression on me. Then one day I stumbled across his autobiography “ Geons, Black Holes and Quantum Foam” . The book brought in me new insight about the man who dedicated all his life for Physics and only Physics.
Wheeler was the forefront theoretical Physicist who worked with Bohr, Einstein and others. He was one among many physicists who developed and shaped the Modern Physics – Physics of 20th Century. Wheeler was well known for his flamboyance, his oratory skill, mastery on language, witty style of presentation.
Max Tegmark, a cosmologist at the MIT, Massachusetts Institute of Technology said of Dr. Wheeler, “For me, he was the last Titan, the only physics superhero still standing.”
"Johnny Wheeler probed far beyond the frontiers of human knowledge, asking questions that later generations of physicists would take up and solve,"
said Kip Thorne, the Feynman Professor of Theoretical Physics at the California Institute of Technology, a leading cosmologist and one of Wheeler's best-known students. "And he was the most influential mentor of young scientists whom I have known."
Wheeler, according to James Peebles, Princeton's Albert Einstein Professor of Science Emeritus, was "something approaching a wonder of nature in the world of physics."
Promissing Young man
John Archibald Wheeler was well known as Johnny in his friends circle. He was born on July 9, 1911 at Jacksonville, Florida. He was the first of four children, to Joseph Lewis Wheeler and Mabel Archibald. They were librarians at Washington D.C., Public Library. As they were moving from one place to other, Johnny grew up in Glendale, California, Youngstown, Ohio, Benson, Vermont, and Baltimore, Maryland. California, Ohio and Vermont and many other places.
Wheeler grew with the books. These books showed the young boy, the exciting world of Science and nature. He recalls those childhood days “with librarian parents, it is not surprising that I grew up among books. In Youngstown, my father used to bring home books so that the family could help evaluate them for possible purchase by the library. He and my mother sit around after supper talking over prospective purchases”
He read J Arthur Thompson's “Outline of Science” when he was 10 and it had lasting impression on him. Franklin Jones' "Mechanisms and Mechanical Movements" also impressed him. He was guided by this book to build a combination lock, a repeating pistol and an adding machine -- all from wood. He built crystal radio sets and strung telegraph wires between his home and his best friend's. Wheeler almost blew off one hand with dynamite one day.
Initially Wheeler studied at Rayen High School and then spent a year at Baltimore City College. He was brilliant in his studies – especially in Maths and Physics. He enrolled himself for scholarship at Johns Hopkins University, where he not only won a prize for debating, but also in other subjects. At the age of 19, Wheeler published his first research paper entitled “The band Spectra of Scandinum, Yitrium and Lanthanum Monoxide” .
Within two year Wheeler was able to get a doctorate at the age of 21. His theses was - on the dispersion and absorption of helium. Pursuing the doctoral studies successfully at the age of 21 showed the signs of brilliance and the promising career to unfold.
Exciting times in Physics
Those were the exciting times in the field of physics. At the end of nineteenth century, many physicists thought that nothing left in Physics. When Max Planck approached a Professor at Berlin University, Professor suggested him to move away from Physics and switch over to any other branch. But that Professor was wrong.
The discovery of X-rays by Roentgen (1895), followed by the discovery of Radioactivity ,by Becquerel (1896) revealed the new world of atoms. Then electrons were discovered by JJ Thomson (1897). The Quantum Theory was proposed by Max Planck (1900). These developments brought new vigor for scientists about Physics. The work of Thomson, Rutherford, Bohr and others unveiled the complicated structure of the atom and the nucleus.
A postdoctoral fellowship from the National Research Council in 1933 allowed Wheeler to continue his studies first at New York University with Gregory Breit. Then he sailed to Copenhagen to work with Bohr, the godfather of the quantum revolution, which had shaken modern science with paradoxical statements about the nature of reality. When he entered the Copenhagen Institute for advanced studies in Physics, there was a man trimming the garden bush with big bush cutter. The man came forward with broad smile and warm shake hand. He was Niels Bohr!
Bohr soon turned his mentor. Wheeler in his autobiography writes “What does a young researcher need at the beginning of career? Perhaps, most of all, a good mentor (Einstein was an exception to the rule. He did brilliant work in isolation). And freedom – freedom to experiment with ideas. Freedom to try new directions, freedom to make mistakes, freedom to think without distraction. In two postdoctoral years, I was blessed with two wonderfully strong mentors Gregory Breit and Niels Bohr”
Wheeler was so much impressed by Bohr that he used to say "You can talk about people like Buddha, Jesus, Moses, Confucius," Wheeler said later, "but the thing that convinced me that such people existed were conversations with NielsBohr”
Wheeler narrates the personality of Niels Boher
“ Bohr was famous in Laboratories and Institutes all over the world. There was the invariable pipe, being incessantly lit but never staying lit. There was the fumbling speech that every one strained to hear. Bohr gave always the appearance of man thinking deeply, very deeply with his deep thoughts struggling to find expression. There was the slow pacing and turning at the front of the room (it was said of him when he visited Los Alamos later that his talk ended when the microphone cord was wound around him as many times as it would go so that he could rotate no longer). When another person was speaking at seminar, Bohr would sit quietly for perhaps fifteen minutes. Then if the subject engaged his attention, he would shift gradually from passive listener to active participant. First a question. Then rising to make a longer point. The end of the hour might find the Bohr at the board with the original speaker listening and trying to get in a few words. In private discussion with me, he was somewhat the same way. I would start talking about what I was working on, and Bohr would say as if his mind elsewhere, “That’s beautiful” or “very interesting”(It was always necessary to “normalize” Bohr’s comments. Beautiful means “probably correct, even if not significant”.”Interesting” meant “not quite entirely trivial”). Then , at some point, Bohr might catch, in what I was saying, one thing that intrigued him. On that point we could have an animated discussion for a while, but it would die down if I did not happen to say something else to spark his interest”
Edwin F. Taylor spent a sabbatical year at Princeton University where he began a collaboration with John Wheeler on an introductory text in special relativity. Taylor writes
“ In San Francisco a commanding position in the Wheeler home hangs a picture of Niels Bohr. It is not possible to write in any detail about John Wheeler without mentioning the central place Niels Bohr held in his esteem and how Bohr's influence shaped him. Others have told me that this influence extended to facial expressions and mannerisms. I never met Niels Bohr, and yet feel I have watched him through John's hesitant, careful, serious speech, his invariant politeness (invariant as observed in every frame of reference!), and his ability to mold a critique from positive comments--traits so charming and insidious that I find myself adopting them, at least in caricature. How similar were their habits of mind I cannot say, yet John's admiration for Bohr was intense and unembarrassed. When John, as a young man, applied to visit Copenhagen, he did so because of his conviction that Niels Bohr had the ability to see farthest into the way physics must develop”
Charming Professor
Wheeler returned to America in 1935, with new ideas and new vigor for research. Soon he moved into family life marrying beautiful lady Janette Hegner on June10, 1935. These couples had long happy fruitful marriage, with a son and two daughters. Mrs Hegner passed away in 2007.
Wheeler was appointed as assistant professor of Physics at the University of North Carolina. His research interest was in nuclear wave functions and its interaction with electromagnetic radiation. Wheeler soon developed the techniques of calculations for the scattering of nuclear waves which proved useful later in particle physics. In 1938, Wheeler joined the Physics faculty at Princeton as an assistant professor where he became legendary figure as scientist and teacher.
In Princeton one day a young fellow came to visit Professor Wheeler. That fellow was awestruck to see young and handsome Professor. The fellow was none other than Richard Feynman, the Genius of 20th Century Physics and the prospective Nobel laureate.
Wheeler told Feynman that they would get together on certain days of the week at certain time for discussions. The day came. As said, Wheeler rushed into the discussion room on that day, kept his watch on the table and discussed. For their next meeting, Feynman also brought a “dollar – watch” , As usual wheeler came in and placed his watch. Feynman took out his big dollar watch and placed in front of Wheelers watch. Wheeler first surprised, then began to smile. The smile then turned into a roaring laughter. Thus the ice was broken between the student Feynman Professor Wheeler. Then onwards their relationship turned into intimate friendship.
Wheeler and Feynman began publishing the epoch making research papers on scattering of electromagnetic radiation in the nuclear field which provided new dimension to particle interaction.
News of Nuclear Fission
On January 16, 1938. Wheeler was excited. A responsibility was entrusted to Wheeler. He had to receive his “Guru” Niels Bohr and his associate Rosenfeld, who will arrive to Hudson Dock, New York from Copenhagen by the ship named MS Drottingholm. The purpose of Bohr visit to discuss with Einstein on Philosophical implications of Quantum Mechanics and also to deliver lectures at Princeton. Bohr and Rosenfeld came to New York. Bohr remained in New York to make discussion with Fermi. Rosenfeld and Wheeler began their journey to Princeton.
During their journey as usual Wheelr asked “Anything new? Rosenfeld said ” Yes, in Germany just now fission of Uranium was discovered”. That was really a big news!
It was in Berlin University, Otto Hahn (1879-1968) and Fritz Strassman, (1902-1980) discovered new thing happening when Uranium target bombarded with stream of slow neutrons. They found that the pure Uranium target now contain traces of Barium and Krypton, which are much lighter. How it can take place? This was the big question for Hahn and Strassman. They sent these results to Lise Meitner (1878-1968) a well trained in Physics was assistant of Hahn in his experiments. At that time she was in Sweden, actually fled from Germany to escape from Nazis.
When Lise Meitner received curious results from Berlin University, she was accompanied with her nephew Otto Robert Frisch (1904-1979), who actually came from Copenhagen. During the long walk in the beautiful fields and surroundings of Sweden, Meitner and Frisch discussed the results and slowly they found the answer. Here the Uranium nucleus captures the neutron and then break up into lighter nuclei – Barium and Krypton. That means Uranium nucleus undergoes fission.
When Frisch when returned to Copenhagen, Bohr and Rosenfeld just to leave to USA. On the board of the ship itself, Frisch hurriedly explained the Berlin experiment and uttered few lines of explanation. That was sufficient for Bohr. He immediately got the point and exclaimed “ Oh, what idiots we all have been. Oh, the this is just as it must be”
During the long voyage , Bohr and Rosenfeld discussed what is happening with Uranium nucleus when that hit by a neutron. After a week of voyage, as the ship was nearing New York, both Bohr and wheeler had clear understanding about the new and exciting phenomenon of Nuclear Fission.
Rosenfeld during the travel with Wheeler to Princeton told all these detail, except that discovery should be kept secret for the time being. Wheeler was so thrilled to know the exciting discovery, nest day itself he arranged a meeting where he announced the new explanation to Berlin Experiment. Thus the news of Nuclear Fission was first leaked by Wheeler.
During Bohrs stay at Princeton, Wheeler and Bohr seriously discussed about the nuclear fission. These discussion ultimately provided one of the most beautiful explanation to Nuclear fission.
They used the liquid drop model of the nucleus. This model was in fact developed by Bohr a few years ago to explain the structure of the nucleus. The model makes analogy of the nucleus and its property with a liquid drop. The spherical shape of the liquid drop, the force of surface Tension, short range molecular forces, the uniform density of the liquid drop, its splitting into smaller droplets by supplying the energy are very much similar to the property of the nucleus. The liquid drop model envisage a theoretical as well as the mental picture of invisible nucleus of an atom.
According to Wheeler and Bohr, when Uranium nucleus captures a neutron it becomes a compound nucleus. The shape of the nucleus changes from spherical to spheroid, then into a dumbbell. The non uniform distribution of positive charges of the nucleus results in the constriction. Ultimately a stage will be reached, when the two bells of the dumbbell move away which causes the fission of a nucleus.
Wheeler and Bohr calculated how much amount of energy is released on the basis of Coulomb interaction between the two nuclear fragments at the time of its detachment. The calculated energy found to be closely matched with the experimentally observed value. This is the simple but profound explanation given by Wheeler and Bohr amply reflect what one can expect when the two genius working together. Wheeler and Bohr published an article "The Mechanism of Nuclear Fission" (1939), which is in fact instrumental in the development of the atomic bomb after a few years.
Wheeler writes in his autobiography “Pure chance played a big role in my involvement in nuclear fission – chance that fission was discovered just as Niels Bohr was about to board a ship for New York, chance that he was headed for Princeton, chance that I was there and prepared to work with him on the theory of nuclear fission”
| Then second world war was broke out. As several great minds of that time participated in Manhattan Project, Wheeler was also actively engaged himself in the development of Nuclear Bomb, They succeeded and what havoc these bombs have created is now a part of a terrible history In 1949-50, Wheeler worked with Teller on the development of the hydrogen bomb, and between 1951 and 1953 he directed the operation of Project Matterhorn, a top-secret project to develop weaponry based on thermonuclear fuel. Wheeler never had any regrets about his participation. He used to say "The largest hospital ever built in the history of the world was built on an island in the Pacific to take care of the casualties expected in the invasion of Japan, and I know that it was never used, and I've been thanked by at least half a dozen men who were slated to take part in the first invasion wave." Indeed, he expressed regret that the bomb had not been ready in time to bring an early end to the war in Europe and possibly save his brother Joe, who died in combat in Italy in 1944. Black hole During all these years Wheeler continued to work on Einstein's theory of gravitation. He was searching for a better understanding of the problem of unifying electromagnetic and gravitational phenomena for which Great Einstein toiled for decades. In 1954 Wheeler suggested a gravitational-electromagnetic entity known as a "geon". What is this peculiar Geon? It is a ball of light radiation held together by its own gravity. This is entirely a new concept. That concept is an effort to unify general relativity with Electromagnetic theory. These efforts were rejuvenated the young minds towards Theoretical Physics at Princeton and soon Wheelers group became the leading American centre of research on General Theory of relativity. Wheeler gave a new concept “Mass without mass” – pure energy holding geon together. He also mooted the idea of “charge without charge” which defy ordinary ideas of charge. The people begin to think Wheeler is turning into really crazy ! Feynman once said “ Wheeler is not appear to be crazy, he is actually crazy!” Indeed, the people working in Science at the highest level always toiling themselves with crazy ideas and appear to be crazy. Wheelers interest in General Theory of Relativity made him to work on the problem of stellar evolution. Actually, the evolutionary of stages of stars have become clearer only in twentieth century. The dynamic equilibrium between the inward gravitational collapse and the outward expansion due to the radiation pressure balances the hydrogen mass and it begin to glow steadily , which we say as star. The tug of war between gravitational squeeze and the radiation due to fusion reaction decides the evolutionary course of a star. From proto star it turns into the red giant phase. Further collapse makes the hot and dense white dwarf. In around 1930, Eddington (1882-1944), the British Astronomer firmly believed and propagated the idea that white dwarf stage is the end of a star. Most of the scientists also believed the same. However, Indian born, American Physicist S Chandrashekhar challenged the concept. Under enormous pressure and temperature, particles of the star moves with extremely high speed. Therefore Chandra employed Theory of Relativity and also Quantum Theory to describe the state of a star. His theoretical calculations indicated the upper limit mass for a white dwarf. Suppose the mass of a white dwarf is more than a critical value, ie 1.41 solar mass, then gravitational collapse overwhelms the outward radiation pressure. This results in other evolutionary stages. When Chandrashekhar proposed his new theory, that theory was seriously ridiculed by Arthur Edington and others. The confrontation of Edngton with Chandra was considered as one of the nastiest thing happened in the modern Astronomy. But Science always relay on absolute truth, not on the status of a person or system. Their objection and criticism could not stand with test of time. Chandrashekhar’s theory turned as the proper explanation of a star. If the mass of a white dwarf exceeds Chandrashekhar limit, then what will be the fate of a star? The gravitational crunch of white dwarf causes a monstrous explosion and it known as Supernova. The core of the star is now so dense that it turnout to be a pulsar which spewing the radiation with a definite period. In around 1950 these ideas were hovering in Physics community. Wheeler speculated that the pulsar may be a neutron star. He was right in his concept. Further gravitational collapse of a star reduces its size further. If its size exceeds a particular limit called Schwarzschild radius (due to Karl Schwarzschild, 1873-1916) , the escape velocity of the star now nearing the velocity of light. That means, even the light can’t escape from it. That star simply swallow the matter and radiation nearby. Nothing can escape from the gravitational clutches of the star. What is the name for the ultimate end of the star? Is it a Dark Star? In fact, British scientist Michel in 16th Century, French Mathematician Laplace in 18th Century speculated the possibility of the existence of such dark stars. However, the name do not give the full picture. Wheeler in 1960s was working in this field. He was interested what happens to space - time under the extremely high gravitational field. He was not happy on calling those exceptionally high gravity stars as “Dark Stars” which prevent rays of light and other radiation to escape from them. One day he stumbled across the name for which he was searching for many years. That is a sort of serendipity! Wheeler narrates that incidence in his autobiography. In 1967, Wheeler was invited to deliver a lecture in a Conference on Pulsars. Wheeler writes “ In my talk, I argued that we should consider the possibility that at the centre of a pulsar there is a gravitationally completely collapsed object. I remarked that one could not keep saying “gravitationally completely collapsed object” over and over. One needed a shorter descriptive phrase. “How about the Black hole?” asked someone in the audience. I had been searching for just the right term for months, mulling it over in bed, in a bath tub, in my car, wherever I had quite moments. Suddenly this name seemed exactly right. When I gave a more formal Sigma Xi Beta Kappa lecture in the West Ballroom of the New York Hilton a few weeks later, on December 29, 1967, I used the term and then included it in the written version of the lecture published in the spring of 1968. (As it turned out, a pulsar is powered by “merely” a neutron star, not a black hole) “I decided to be casual about the term “black hole” dropping it into the lecture and the written version as if it were an old familiar friend. Would it catch on? Indeed it did. By now every school child has heard the term. Richard Feynman, when he saw the term, chided me. In his mind, it was suggestive. He accused me of being naughty. In fact, the name black hole has a lineage. That is why it caught my fancy. Since at least the 1890s, the term “black body” has been used in Physics to describe an idealized body that absorbs all radiation that falls upon it, and emits radiation at the maximum rate possible for a given temperature. The blackbody is a perfect absorber and as perfect an emitter as it is possible to be. A black hole has one of these characteristics, but not the other. It absorbs everything that falls upon it. It emits nothing. Thus black hole seems the ideal name for this entity. The geometry of space-time near a black hole, funneling into ever greater curvature, adds to the appropriate of the name” Since black hole do not reveal its information to the outside world, Wheeler fancied to coin the phrase “ A black hole has no hair” Though the Nobel, which many thought he deserved, eluded Wheeler, he won numerous awards for his work, including the US Atomic Energy Commission's Enrico Fermi Award in 1968. His passion for teaching was amazing. His best quote is “There are students in the University to teach the Professors” Looking back over his own career, Wheeler divided it into three parts. Until the 1950s, a phase he called "Everything Is Particles," he was looking for ways to build all basic entities, such as neutrons and protons, out of the lightest, most fundamental particles. The second part, which he termed "Everything Is Fields," was when he viewed the world as one made out of fields in which particles were mere manifestations of electrical, magnetic and gravitational fields and space-time itself. More recently, in a period he viewed as "Everything Is Information," he focused on the idea that logic and information is the bedrock of physical theory. Archibald wheeler once said “Throughout ‘my long career of teaching and research and public service it has been interaction with young minds that has been my greatest stimulus and my greatest reward. That reward comes back again with compound interest as I hear now from so many former students who let me know what they are up to and how their early wrestling with deep questions in Physics helped to shape their lives. Not just graduate students. Even more numerous have been the scores of undergraduates who brought their enthusiasm and fresh perspective to the questions I put to them and who helped me to see more clearly. But I am still too busy, too busy searching, to spend much time looking back. As Niels Bohr’s friend Piet Hein puts it in another of his grooks I’d like to know What this whole show Is all about Before it’s out. Indeed, the real show man Archibald Wheeler quietly gone from this world to un known territory – a black hole, who knows! But the show is going on for we to search absolute truth. |
