AdamSmith Posted October 4, 2017 Posted October 4, 2017 Heisenberg's view was tolerant. Pauli, raised as a Catholic, had kept silent after some initial remarks, but when finally he was asked for his opinion, said: "Well, our friend Dirac has got a religion and its guiding principle is 'There is no God and Paul Dirac is His prophet.'" Everybody, including Dirac, burst into laughter.[40][41]
AdamSmith Posted October 4, 2017 Posted October 4, 2017 Later in life, Dirac's views towards the idea of God were less acerbic. As an author of an article appearing in the May 1963 edition of Scientific American, Dirac wrote: It seems to be one of the fundamental features of nature that fundamental physical laws are described in terms of a mathematical theory of great beauty and power, needing quite a high standard of mathematics for one to understand it. You may wonder: Why is nature constructed along these lines? One can only answer that our present knowledge seems to show that nature is so constructed. We simply have to accept it. One could perhaps describe the situation by saying that God is a mathematician of a very high order, and He used very advanced mathematics in constructing the universe. Our feeble attempts at mathematics enable us to understand a bit of the universe, and as we proceed to develop higher and higher mathematics we can hope to understand the universe better.[42]
AdamSmith Posted October 4, 2017 Posted October 4, 2017 In 1971, at a conference meeting, Dirac expressed his views on the existence of God.[43] Dirac explained that the existence of God could only be justified if an improbable event were to have taken place in the past: It could be that it is extremely difficult to start life. It might be that it is so difficult to start life that it has happened only once among all the planets... Let us consider, just as a conjecture, that the chance of life starting when we have got suitable physical conditions is 10−100. I don't have any logical reason for proposing this figure, I just want you to consider it as a possibility. Under those conditions ... it is almost certain that life would not have started. And I feel that under those conditions it will be necessary to assume the existence of a god to start off life. I would like, therefore, to set up this connexion between the existence of a god and the physical laws: if physical laws are such that to start off life involves an excessively small chance, so that it will not be reasonable to suppose that life would have started just by blind chance, then there must be a god, and such a god would probably be showing his influence in the quantum jumps which are taking place later on. On the other hand, if life can start very easily and does not need any divine influence, then I will say that there is no god.[43]
AdamSmith Posted October 4, 2017 Posted October 4, 2017 Dirac's grave in Roselawn Cemetery, Tallahassee, Florida. Also buried is his wife Manci (Margit Wigner). Their daughter Mary Elizabeth Dirac, who died 20 January 2007, is buried next to them but not shown in the photograph.
AdamSmith Posted October 4, 2017 Posted October 4, 2017 The commemorative marker in Westminster Abbey. [The symbols are the most compact formulation of his relativistic equation for the electron: the Dirac equation.]
AdamSmith Posted October 4, 2017 Posted October 4, 2017 Only deep nerds need attend the following. Dirac established the most general theory of quantum mechanics and discovered the relativistic equation for the electron, which now bears his name. The remarkable notion of an antiparticle to each fermion particle – e.g. the positron as antiparticle to the electron – stems from his equation. He was the first to develop quantum field theory, which underlies all theoretical work on sub-atomic or "elementary" particles today, work that is fundamental to our understanding of the forces of nature. He proposed and investigated the concept of a magnetic monopole, an object not yet known empirically, as a means of bringing even greater symmetry to James Clerk Maxwell's equations of electromagnetism. Gravity He quantised the gravitational field, and developed a general theory of quantum field theories with dynamical constraints, which forms the basis of the gauge theories and superstring theories of today. The influence and importance of his work has increased with the decades, and physicists use the concepts and equations that he developed daily. Quantum theory Dirac's first step into a new quantum theory was taken late in September 1925. Ralph Fowler, his research supervisor, had received a proof copy of an exploratory paper by Werner Heisenberg in the framework of the old quantum theory of Bohr and Sommerfeld. Heisenberg leaned heavily on Bohr's correspondence principle but changed the equations so that they involved directly observable quantities, leading to the matrix formulation of quantum mechanics. Fowler sent Heisenberg's paper on to Dirac, who was on vacation in Bristol, asking him to look into this paper carefully. Dirac's attention was drawn to a mysterious mathematical relationship, at first sight unintelligible, that Heisenberg had reached. Several weeks later, back in Cambridge, Dirac suddenly recognised that this mathematical form had the same structure as the Poisson brackets that occur in the classical dynamics of particle motion. From this thought he quickly developed a quantum theory that was based on non-commuting dynamical variables. This led him to a more profound and significant general formulation of quantum mechanics than was achieved by any other worker in this field.[51] Dirac's formulation allowed him to obtain the quantisation rules in a novel and more illuminating manner. For this work,[52] published in 1926, Dirac received a PhD from Cambridge. This formed the basis for Fermi-Dirac statistics that applies to systems consisting of many identical spin 1/2 particles (i.e. that obey the Pauli exclusion principle), e.g. electrons in solids and liquids, and importantly to the field of conduction in semi-conductors. Dirac was famously not bothered by issues of interpretation in quantum theory. In fact, in a paper published in a book in his honour, he wrote: "The interpretation of quantum mechanics has been dealt with by many authors, and I do not want to discuss it here. I want to deal with more fundamental things."[53] The Dirac equation For more details on this topic, see Dirac equation. In 1928, building on 2×2 spin matrices which he purported to have discovered independently of Wolfgang Pauli's work on non-relativistic spin systems (Dirac told Abraham Pais, "I believe I got these [matrices] independently of Pauli and possibly Pauli got these independently of me."),[54] he proposed the Dirac equation as a relativistic equation of motion for the wave function of the electron.[55] This work led Dirac to predict the existence of the positron, the electron's antiparticle, which he interpreted in terms of what came to be called the Dirac sea.[56] The positron was observed by Carl Anderson in 1932. Dirac's equation also contributed to explaining the origin of quantum spin as a relativistic phenomenon. The necessity of fermions (matter) being created and destroyed in Enrico Fermi's 1934 theory of beta decay led to a reinterpretation of Dirac's equation as a "classical" field equation for any point particle of spin ħ/2, itself subject to quantisation conditions involving anti-commutators. Thus reinterpreted, in 1934 by Werner Heisenberg, as a (quantum) field equation accurately describing all elementary matter particles – today quarks and leptons – this Dirac field equation is as central to theoretical physics as the Maxwell, Yang–Mills and Einstein field equations. Dirac is regarded as the founder of quantum electrodynamics, being the first to use that term. He also introduced the idea of vacuum polarisation in the early 1930s. This work was key to the development of quantum mechanics by the next generation of theorists, in particular Schwinger, Feynman, Sin-Itiro Tomonaga and Dyson in their formulation of quantum electrodynamics. Dirac's Principles of Quantum Mechanics, published in 1930, is a landmark in the history of science. It quickly became one of the standard textbooks on the subject and is still used today. In that book, Dirac incorporated the previous work of Werner Heisenberg on matrix mechanics and of Erwin Schrödinger on wave mechanics into a single mathematical formalism that associates measurable quantities to operators acting on the Hilbert space of vectors that describe the state of a physical system. The book also introduced the delta function. Following his 1939 article,[57] he also included the bra–ket notation in the third edition of his book,[58] thereby contributing to its universal use nowadays. Magnetic monopoles In 1931, Dirac proposed that the existence of a single magnetic monopole in the universe would suffice to explain the quantisation of electrical charge.[59] In 1975,[60] 1982,[61] and 2009[62][63][64] intriguing results suggested the possible detection of magnetic monopoles, but there is, to date, no direct evidence for their existence (see also Magnetic monopole#Searches for magnetic monopoles). Tomcal 1
AdamSmith Posted October 5, 2017 Posted October 5, 2017 Freeman Dyson: Feynman would just write down the solutions without ever writing the equations. It seemed like a sort of magic. After the war, you went to Cornell as a graduate student in the late ’40s, and you ended up working with one of the towering figures in physics, Hans Bethe. Did he become your mentor? Yes, very much so, an extraordinarily good one. He was amazing with students. He had a lot of students and he always found the right problem for each student, just difficult enough but not too difficult. He was an ideal person to have as a mentor. I owe a tremendous amount to him. What was the right problem for you? It concerned quantum molecular dynamics, which was bursting open at that time. There was a group of experimenters at Columbia who had been looking at the hydrogen atom with tools they developed during the war. Microwaves were invented for military purposes—for radar—and microwaves were just what you needed to study quantum mechanics with great accuracy. Willis Lamb was the chief experimenter, and he was tickling the hydrogen atom, measuring very precisely the energy levels of hydrogen. It turned out the standard quantum theory gave the wrong answers, so something new was needed and Bethe understood what it was. If you put the reaction of the atom’s radiation field onto its mechanics, it gave the right kind of behavior. Bethe had this extraordinary ability to do simple calculations which were quite sloppy but gave roughly the right answer. Then he gave me the problem of doing the same calculation, which I did much more accurately. http://nautil.us/issue/43/heroes/my-life-with-the-physics-dream-team Tomcal 1
AdamSmith Posted October 5, 2017 Posted October 5, 2017 Then you met Richard Feynman and you ended up working with him on quantum electrodynamics. I never worked with Feynman, but I learned a tremendous lot from him. He was a young professor and I was just a student, so I listened to Feynman, and of course he was a genius. He was also a clown and loved to perform, so he always needed an audience. I was very happy to be the audience. What made Feynman different from other scientists? He was extremely original. He had his own way of doing science, which was different from everybody else. That’s why he had a hard time communicating. He never wrote down equations. Most people in physics write down an equation and then find the solutions, but that wasn’t the way Feynman did it. Feynman would just write down the solutions without ever writing the equations. It seemed like a sort of magic because he thought in terms of pictures instead of equations. He had these little pictures in his head and he scribbled little pictures on paper and nobody understood what they meant. My job was to translate Feynman into language other people could understand. Tomcal 1
AdamSmith Posted October 5, 2017 Posted October 5, 2017 You never actually got your Ph.D., did you? No. I was so lucky. I slipped through the cracks. You didn’t want a Ph.D.? No, I hate the Ph.D. I think it destroys people’s lives. I had actually three tragedies which I witnessed with people who came to work with me and came to grief. One of them committed suicide and two ended up in mental institutions. I blame the Ph.D. system for that. I think it really was a disaster for many people. Why? Because the Ph.D. system grinds people down? Yes, and it’s completely inappropriate for what most people need. It was designed for German academics in the 19th century and it was fine for that. But for any other kind of life, it’s totally wrong. It takes far too long. It forces you to pretend to be a researcher when most people don’t want to be researchers. It’s become a union card and I think it’s highly disruptive, particularly bad for women. For women to waste five or 10 years of their lives is more of a disaster than it is for men. Because they might have family responsibilities as well? Yes, because there’s a biological clock. It’s ticking much more for them. Tomcal 1
AdamSmith Posted October 5, 2017 Posted October 5, 2017 Do you need to be willing to risk your reputation and pursue crazy ideas? Is that what leads to great breakthroughs? First of all, it helps to be ignorant. The time when I did my best work was when I was most ignorant. Knowing too much is a great handicap. Especially if you’ve been teaching for some years, things get so fixed in your mind and it’s impossible to think outside the box. I was in the lucky position of jumping into physics without ever having taken any courses in physics. I’d only been a pure mathematician up to that point. Is the great scientist also naturally subversive? Yes, undoubtedly. You’ve got to destroy what exists in order to build something new. You need good taste, of course. If you destroy indiscriminately, it doesn’t help at all. That’s where intuition comes in—what parts of the old building should be taken down. Tomcal 1
AdamSmith Posted October 5, 2017 Posted October 5, 2017 "If at first the idea is not absurd, then there is no hope for it." Einstein
AdamSmith Posted October 6, 2017 Posted October 6, 2017 Feynman: So I used to pick the locks all the time and point out that it was very easy to do. And every time we had a meeting of everybody together, I would get up and say that we have important secrets and we shouldn't keep them in such things; we need better locks. One day Teller got up at the meeting, and he said to me, “Well, I don't keep my most important secrets in my filing cabinet; I keep them in my desk drawer. Isn't that better?" I said, “I don't know. I haven't seen your desk drawer.” Well, he was sitting near the front of the meeting, and I'm sitting further back. So the meeting continues, and I sneak out and go down to see his desk drawer. OK? I don't even have to pick the lock on the desk drawer. It turns out that if you put your hand in the back, underneath, you can pull out the paper like those toilet paper dispensers. You pull out one, it pulls another, it pulls another ... I emptied the whole damn drawer, put everything away to one side, and went back upstairs. The meeting was just ending, and everybody was coming out, and I joined the crew and ran to catch up with Teller, and I said, “Oh, by the way, let me see your desk drawer." "Certainly, “ he said, and he showed me the desk. I looked at it and said, “That looks pretty good to me. Let's see what you have in there. "I'll be very glad to show it to you, “ he said, putting in the key and opening the drawer.” If , “ he said, “ you hadn't already seen it yourself." The trouble with playing a trick on a highly intelligent man like Mr. Teller is that the time it takes him to figure out from the moment that he sees there is something wrong till he understands exactly what happened is too damn small to give you any pleasure! http://calteches.library.caltech.edu/34/3/FeynmanLosAlamos.htm
AdamSmith Posted October 6, 2017 Posted October 6, 2017 6 hours ago, AdamSmith said: Oration in Memory of Abraham Lincoln, Washington, D.C., April 14, 1876 by Frederick Douglass http://etc.usf.edu/lit2go/184/a-lincoln-anthology/4823/oration-in-memory-of-abraham-lincoln-washington-dc-april-14-1876
