Ed Witten on String Theory

Ed Witten

Here’s what TIME magazine said about Ed Witten back in 2004 when he was chosen as one of its 100 most influential people:

Albert Einstein labored unsuccessfully for decades to create a theory that would merge relativity and quantum physics into one tidy mathematical package. But where Einstein failed, physicists may finally be on the verge of success, largely thanks to Edward Witten, generally considered the greatest theoretical physicist in the world. “Ed is unique,” says John Schwarz, a theorist at Caltech, “the kind of person who comes along once a century.”

The tall, thin, soft-spoken Witten, 52, didn’t even set out to be a scientist. He majored in history at Brandeis and originally planned to be a journalist but ended up getting a Ph.D. in physics instead. By the mid-1980s, some of his colleagues had decided that the answer to Einstein’s failed dream was to treat the building blocks of matter–quarks, photons, electrons and such–as minuscule, vibrating strings of energy rather than as particles. But superstring theory was considered no more than an esoteric and eccentric subspecialty until Witten (by this time a full professor at Princeton) turned his attention to it. Before long he was the dominant player in the field, and string theory was the hottest area of physics. Many of the big developments in string physics–the kind of ideas that break through theoretical logjams and bring everyone to a deeper level of understanding–can be traced to Witten. “Most other people have made one or two such contributions,” says Juan Maldacena, who, like Witten, is at Einstein’s old stomping ground, the Institute for Advanced Study in Princeton. “Ed has made 10 or 15.”

What sort of contributions? Don’t ask, unless twistor-space methods and Yang-Mills theories are your cup of tea. But if Witten’s string theory is right, it means that the quest Einstein began to find the ultimate laws of the universe may nearly be over. The proof, however, may still be many years off. Witten once called string theory “a bit of 21st century physics that somehow dropped into the 20th century.” If so, Witten clearly has the 21st century mind to handle it.

Enough said. Here’s Witten on string theory:

Steven Weinberg on the LHC, the Higgs boson, dark matter and supersymmetry

Physicists hope that CERN’s Large Hadron Collider, the world’s most powerful particle accelerator, will help answer some of the most intriguing and pressing questions in physics. Steven Weinberg shared the 1979 the Nobel Prize for physics with Sheldon Glashow and Abdus Salam ‘for their contributions to the theory of the unified weak and electromagnetic interaction between elementary particles, including inter alla the prediction of the weak neutral current’.

L to R: Sheldon Glashow, Abdus Salam and Steven Weinberg receiving the 1979 Nobel Prize for Physics

In this lecture Weinberg discusses the standard model of particle physics – to which he made major contributions – the Higgs boson, the nature of dark matter and the theory of supersymmetry.

Dangerous Knowledge

A BBC documentary about the lives and work of Georg Cantor, Ludwig Boltzmann, Kurt Godel and Alan Turing.One went insane, another starved himself to death and two committed suicide. Find out why.

From top left: Cantor, Boltzmann, Turing and Godel

Brian Greene: The Universe on a String

Brian Greene

A wonderfully engaging TED talk on superstring theory by the physicist Brian Greene. If you haven’t already, its a must see. Greene’s a class act.

Einstein, Bohr and John Wheeler

John Wheeler with the busts of Einstein and Bohr

During a conference in Warsaw in June 1976, the celebrated American physicist John Wheeler gave an interview to the Czechoslovak Journal of Physics A. It was originally published in Czech and an English translation first appeared in General Relativity and Gravitation 41 (2009), 679-689, the special issue dedicated to the memory of Wheeler who died in April 2008 aged 96.

Beginning in 1938 Wheeler spent almost 40 years at Princeton University where among his postgraduate students were Richard Feynman and Hugh Everett III. He was one of the few physicists who worked with Bohr and knew Einstein well during his Princeton years. Here’s what Wheeler had to say about both men and he recounts the day Bohr ended up debating the interpretation of quantum mechanics with a stark naked Einstein stretched out on a couch.

Albert Einstein, Hideki Yukawa and John Wheeler in Princeton 1954

WheelerIt has been a wonderful inspiration to know both men. I first came to know Einstein in 1934 on my first visit to Princeton, very shortly after he had come to the United States. And then in 1953, I remember when I first started to teach relativity that although it was only 18 months before his death, he was kind enough to invite me to bring my students around to his house for tea. So we sat around the dining-room table and his secretary Helen Dukas and his stepdaughter Margot Einstein brought tea and students asked Einstein questions.

One of them: “Professor Einstein, what do you think about the nature of electricity?” and he told about his thoughts over the years about electricity. And another one: “Professor Einstein, do you agree with the idea of an expanding universe?” and, of course, he did. And another student: “Professor Einstein, you had so much to do with the quantum theory and why don’t you agree with the quantum theory?” And then Einstein said again that he did so often in his famous words: “I do not believe that God plays dice.” And finally one student got up his courage and he said: “Professor Einstein, when you are no longer living, what will happen to this house?” And Einstein gave a great big laugh, he threw up his hands and with his hearty voice he spoke with a childlike simplicity and smile on his face and bright eyes—and his choice of words was always so careful and so beautiful: “This house will never become a place of pilgrimage where the pilgrims come to look at the bones of the saint.” And so it is today. The tourist buses drive up in the front of his house and people get out and photograph the outside but they do not go in the inside.

 And then Bohr, Bohr the greatest leader of physics and father-figure of all physicists. I went to Copenhagen and I can remember, as a student applying for a fellowship, the words I put down in my application for the fellowship—why I wanted to go. That was in 1934, very early 1934. Why did I want to go to work with Bohr in Copenhagen? It was because “he has the power to see further ahead in physics than any other man alive”. From my arrival in September I saw his great gift to think deeply in nuclear physics. There in Copenhagen in the spring of 1935 Christian Møller, fresh back from Rome, reported Fermi’s results on the capture of slow neutrons. Bohr immediately became terribly concerned, interrupted, walked up and down, talked and talked, and as he talked one could see the liquid drop model of the nucleus taking shape right there before one’s eyes. For him no physics was of any interest unless it yielded some paradox or some beautiful way of seeing things simply. I do not remember anyone at Bohr’s institute who ever succeeded in finishing a seminar talk, even though he was the invited speaker. He might be able to speak five minutes, he might be able to speak fifteen minutes, but soon Bohr would take over and would use the whole time discussing the meaning of the speaker’s results and what they proved and what they did not prove.

 I became involved with Bohr on nuclear fission at the time when he brought word of the discovery of fission to the United States on the sixteenth of January in 1939. I was down at the waterfront pier in New York and I had hardly said “Hello” when he took me aside and started to tell me that on this very ship just before he left Copenhagen he had been told about the discovery of Hahn and Strassmann. So we dropped everything else and started to work on fission. I can remember rushing—we worked at night as well as in the day—rushing up the steps in the library—from my office to the library— to look at the dictionary to see whether there is a better word than “fission”. “Fission” had an unfortunate property. The noun is all right but there is no good verb. A nucleus “fissions” is not a very nice verb, but we stayed with “fission” in spite of that.

During the war, I met Bohr in Washington at the time he was dividing his time between Los Alamos and Washington after he had escaped from Denmark in a small boat over the sea into Sweden. He told me confidentially about his discussions with President Roosevelt about the future of nuclear energy. He told me about his efforts to work out some control of nuclear energy after the war. He said, “It may seem strange, how can such a man as I speak to the president of the greatest country of the World at the time of the greatest war in the history of the world. But”, he said, “I put it to him as man to man simply in terms of what the problem is and what other possibility is there than this.” Bohr made a great impression on Roosevelt and they had several discussions. The last speech that Roosevelt wrote—he died while he was still working on that speech—had in it some words, quoted by Roosevelt from Thomas Jefferson, about how scientists serve as the most important means of communication and bringing peace between the different countries of the world. It was enormously impressive to me to see Bohr’s courage in facing up to what the great questions are. I can remember his particularly saying to me at one time: “I must seem always to you like an amateur. But I am always an amateur.” Of course, it’s a very modest way to say that one is a pioneer, an explorer. If you are working on something new, then you are necessarily an amateur.

Einstein and Bohr at the Sixth Solvay Conference, 1930

Wheeler on the Einstein-Bohr Debate:

To me the debate between Bohr and Einstein over the years is the greatest debate in all the history of human thought. I can’t think of any greater men debating any deeper issue. It took place for a number of years in Europe and then for a number of years in America. Unfortunately, the artists of the West seem not to be so much aware of science. But in 1971, on an earlier visit to Moscow, I visited a studio in the basement of an apartment house where two sculptors were making sculptures of artists and poets, and great thinkers, and great scientists. There was a sculpture of Bohr and Einstein debating. It was wonderful to see that. But I did not tell the sculptors about one of the times when Bohr came to visit the house of Einstein that I just mentioned. He went up the stairs to the second floor where Einstein’s study was and—it was a terribly hot day—he found Einstein lying on the sofa with not one piece of clothing on. Well, they continued the debate in that frame of reference. The sculptors did not know that.

The debate concerned what to my mind concerns the deepest, the most mysterious, the most challenging idea in all of physics, the quantum principle, the overarching principle of twentieth century physics. As you know, while Einstein was still in Europe the debate focused on Einstein’s belief that quantum theory was inconsistent. He did not only talk. He tried to give a proof that the uncertainty principle is logically inconsistent. At the famous Solvay Congress of October 1930 Einstein confronted Bohr with his idealized experiment. How dramatic it was when Bohr turned the tables and used Einstein’s own general relativity to prove that Einstein’s scheme would not work! After Einstein came to the United States, he gave up trying to prove that quantum theory is inconsistent. He now tried to prove that the quantum theory is incompatible with any reasonable idea of reality. His efforts led to the famous Einstein–Rosen– Podolsky “paradox” which at the hands of Bohr and Bell and others has brought us so much understanding.

We shall have to let science unroll through the years ahead before we can look back and know which is the greater man because we know each new generation has new insight on history. But to me the two men had so much in common. They were so happy talking with each other. They were always concerned with the deepest problems, not only problems of physics but the deepest problems of mankind.

The full interview can be found here and more about John Wheeler here.

Marcus du Sautoy on Symmetry

In this entertaining lecture Marcus du Sautoy talks about his quest to discover symmetry in mathematics and in life.

Einstein Documentary I

An excellent documentary about the life and times of Albert Einstein from the American Masters series for PBS. Einstein qualifies because he became a US citizen in 1940.