American theoretical physicist (1933-2021)
(Redirected from Lectures on Quantum Mechanics (Weinberg))
Steven Weinberg (born 3 May 1933 - 23 July 2021) was an American physicist. He was awarded the 1979 Nobel Prize in Physics (with colleagues Abdus Salam and Sheldon Glashow) for combining electromagnetism and the weak force into the electroweak force.
- ... most physicists would probably agree that the place of local fields is nowhere so secure as in the the theory of photons and gravitons, whose properties seem indissolubly linked with the space-time concepts of gauge invariance (of the second kind) and/or Einstein's equivalence principle.
- (1964). "Photons and gravitons in S-matrix theory: derivation of charge conservation and equality of gravitational and inertial mass". Physical Review 135 (4B): B1049–1056. (quote from p. B1049)
- As everyone today knows, in specifying the value of a gauge coupling constant it is necessary to say not only what its value is but where — that is at what normalization scale — it has that value.
- "Calculation of fine structure constants." In Fourth Workshop on Grand Unification, pp. 380–394. Birkhäuser, Boston, MA, 1983. doi:10.1007/978-1-4757-1812-6_23 (page 390)
- Elementary particles are terribly boring, which is one reason why we're so interested in them.
- "Elementary particles and the laws of Physics" in The 1986 Dirac Memorial Lectures (1987)
- Considering the pervasive importance of quantum mechanics in modern physics, it is odd how rarely one hears of efforts to test quantum mechanics experimentally with high precision.…The trouble is that it is very difficult to find any logically consistent generalization of quantum mechanics. One obvious target for generalization is the linearity of quantum mechanics, but if we arbitrarily add nonlinear terms to the Schrodinger equation, how do we know that the theory we obtain will have a sensible physical interpretation? At least in part, it is the dearth of generalized versions of quantum mechanics that has made it so hard to plan experimental tests of quantum mechanics.
- "Testing Quantum Mechanics", Annals of Physics (1989)
- The more the universe seems comprehensible, the more it also seems pointless.
- Dreams of a Final Theory: The Search for the Fundamental Laws of Nature (1993), ISBN 0-09-922391-0.
- So what happens to the effective field theories of electroweak, strong, and gravitational interactions at energies of order 1015–1018 GeV? I know of only two plausible alternatives. One possibility is that the theory remains a quantum field theory, but one in which the finite or infinite number of renormalized couplings do not run off to infinity with increasing energy, but hit a fixed point of the renormalizable group equations. ... The other possibility, which I have to admit is a priori more likely, is that at very high energy we will run into really new physics, not describable in terms of a quantum field theory. I think that by far the most likely possibility is that this will be something like a string theory.
- "What is quantum field theory, and what did we think it is?", arXiv preprint hep-th/9702027 (1997) (pp. 12–13)
- Either by God you mean something definite or you don't mean something definite. If by God you mean a personality who is concerned about human beings, who did all this out of love for human beings, who watches us and who intervenes, then I would have to say in the first place how do you know, what makes you think so? And in the second place, is that really an explanation? If that's true, what explains that? Why is there such a God? It isn't the end of the chain of whys, it just is another step, and you have to take the step beyond that.
- If you have bought one of those T-shirts with Maxwell's equations on the front, you may have to worry about its going out of style, but not about its becoming false. We will go on teaching Maxwellian electrodynamics as long as there are scientists.
- "The Revolution That Didn't Happen" in The New York Review of Books (1998) 
- Religion is an insult to human dignity. With or without it you would have good people doing good things and evil people doing evil things. But for good people to do evil things, that takes religion.
- Address at the Conference on Cosmic Design, American Association for the Advancement of Science, Washington, D.C. (April 1999)
- This comment is modified in a later article derived from these talks:
- Frederick Douglass told in his Narrative how his condition as a slave became worse when his master underwent a religious conversion that allowed him to justify slavery as the punishment of the children of Ham. Mark Twain described his mother as a genuinely good person, whose soft heart pitied even Satan, but who had no doubt about the legitimacy of slavery, because in years of living in antebellum Missouri she had never heard any sermon opposing slavery, but only countless sermons preaching that slavery was God's will. With or without religion, good people can behave well and bad people can do evil; but for good people to do evil — that takes religion.
- One of the great achievements of science has been, if not to make it impossible for intelligent people to be religious, then at least to make it possible for them not to be religious. We should not retreat from this accomplishment.
- Address at the Conference on Cosmic Design, American Association for the Advancement of Science, Washington, D.C. (April 1999)
- In trying to get votes for the Superconducting Super Collider, I was very much involved in lobbying members of Congress, testifying to them, bothering them, and I never heard any of them talk about postmodernism or social constructivism. You have to be very learned to be that wrong.
- "Night Thoughts of a Quantum Physicist" (February 1995); republished in Facing Up: Science And Its Cultural Adversaries (2001)
- It seems to me that we are in the position of a company of players who have by chance found their way into a great theater. Outside, the city streets are dark and lifeless, but in the theater the lights are on, the air is warm, and the walls are wonderfully decorated. However, no scripts are found, so the players begin to improvise—a little psychological drama, a little poetry, whatever comes to mind. Some even set themselves to explain the stage machinery. The players do not forget that they are just amusing themselves, and that they will have to return to the darkness outside the theater, but while on the stage they do their best to give a good performance. I suppose that this is a rather melancholy view of human life, but melancholy is one of the distinctive creations of our species, and not without its own consolations.
- Facing Up: Science and Its Cultural Adversaries pp. 47–48 (2001)
- It seems that scientists are often attracted to beautiful theories in the way that insects are attracted to flowers — not by logical deduction, but by something like a sense of smell.
- Physics Today (November 2005) page 35
- There are those whose views about religion are not very different from my own, but who nevertheless feel that we should try to damp down the conflict, that we should compromise it. … I respect their views and I understand their motives, and I don't condemn them, but I'm not having it. To me, the conflict between science and religion is more important than these issues of science education or even environmentalism. I think the world needs to wake up from its long nightmare of religious belief; and anything that we scientists can do to weaken the hold of religion should be done, and may in fact be our greatest contribution to civilization.
- Closing statements of presentation at Beyond Belief : Science, Religion, Reason and Survival (5 November 2006)
- A superconductor of any kind is nothing more or less than a material in which a particular symmetry of the laws of nature, electromagnetic gauge invariance, is spontaneously broken. ... These rotations act on a two-dimensional vector, whose two components are the real and imaginary parts of the electron field, the quantum mechanical operator that in quantum field theories of matter destroys electrons. The rotation angle of the broken symmetry group can vary with location in the superconductor, and then the symmetry transformations also affect the electromagnetic potentials ... The symmetry breaking in a superconductor leaves unbroken a rotation by 180°, which simply changes the sign of the electron field. In consequence of this spontaneous symmetry breaking, products of any even number of electron fields have non-vanishing expectation values in a superconductor, though a single electron field does not. All of the dramatic exact properties of superconductors – zero electrical resistance, the expelling of magnetic fields from superconductors known as the Meissner effect, the quantization of magnetic flux through a thick superconducting ring, and the Josephson formula for the frequency of the AC current at a junction between two superconductors with different voltages – follow from the assumption that electromagnetic gauge invariance is broken in this way, with no need to inquire into the mechanism by which the symmetry is broken.
- From BCS to LHC. CERN Courier (21 January 2008).
- If there is no point in the universe that we discover by the methods of science, there is a point that we can give the universe by the way we live, by loving each other, by discovering things about nature, by creating works of art. And that—in a way, although we are not the stars in a cosmic drama, if the only drama we're starring in is one that we are making up as we go along, it is not entirely ignoble that faced with this unloving, impersonal universe we make a little island of warmth and love and science and art for ourselves. That's not an entirely despicable role for us to play.
- Quoted in Frankenberry The Faith of Scientists: In Their Own Words (2008), p. 336
- Källén's kindness to me and my wife went beyond his help with this research. He had my wife and me to dinner at his house and at that dinner I went to the bathroom and I learned something about Källén that I don't think anyone knows. And that is that he had hand towels embroidered with the Dirac equation. And I mentioned this to Mrs. Källén and she said they were a present from Pauli.
- (January 14, 2022)"Weinberg "Living with infinities" - Källén Lecture 2009". Andrea Idini, YouTube. (quote at 10:15 of 1:28:03 in video; lecture recorded on February 13, 2009)
- A theorist today is hardly considered respectable if he or she has not introduced at least one new particle for which there is no experimental evidence.
- "Particle physics, from Rutherford to the LHC," Physics Today 64, no.8 (August 2011), 29-33, on 30.
- In fact, there is something puzzling about the Higgs mass we now do observe. It is generally known as the “hierarchy problem.” Since it is the Higgs mass that sets the scale for the masses of all other known elementary particles, one might guess that it should be similar to another mass that plays a fundamental role in physics, the so-called Planck mass, which is the fundamental unit of mass in the theory of gravitation. (It is the mass of hypothetical particles whose gravitational attraction for one another would be as strong as the electric force between two electrons separated by the same distance.) But the Planck mass is about a hundred thousand trillion times larger than the Higgs mass. So, although the Higgs particle is so heavy that a giant particle collider was needed to create it, we still have to ask, why is the Higgs mass so small?
- "The Big Higgs Question", The New York Review of Books, 9 July 2012
- There’s something I’ve been working on for more than a year — maybe it’s just an old man’s obsession, but I’m trying to find an approach to quantum mechanics that makes more sense than existing approaches. I’ve just finished editing the second edition of my book, Lectures on Quantum Mechanics, in which I think I strengthen the argument that none of the existing interpretations of quantum mechanics are entirely satisfactory.
- Steven Weinberg, in "Science’s Path From Myth to Multiverse" by Dan Falk (March 17, 2015)
- It doesn't work to build half an accelerator. The particles need to go all the way around.
- Having taught quantum mechanics and written a book about it recently — a technical treatise — I find that I am not as happy about quantum mechanics as I used to be — not as dismissive of the critics. And it's a bad sign in particular that those physicists who are happy about quantum mechanics — who don't see anything wrong with it — don't agree with each other about what it means. ... And the problem has specifically to do with the act of measurement.
- (November 5, 2016)"2016 Patrusky Lecture: Steven Weinberg on What's the matter with quantum mechanics?". CASW ScienceWriting. (quote at 17:35 of 1:05:21 in video; 4th Patrusky Lecture delivered on October 20, 2016 in San Antonio, Texas)
- Symmetry is not enough by itself. In electromagnetism, for example, if you write down all the symmetries we know, such as Lorentz invariance and gauge invariance, you don’t get a unique theory that predicts the magnetic moment of the electron. The only way to do that is to add the principle of renormalisability – which dictates a high degree of simplicity in the theory and excludes these additional terms that would have changed the magnetic moment of the electron from the value Schwinger calculated in 1948.
- as quoted in an interview by Matthew Chalmers: (13 October 2017)"Model physicist". CERN Courier.
- One of the things that excited me so much about quantum chromodynamics after the work of Gross and Wilczek and Politzer was that it seemed to provide a rational explanation for what had always been mysterious to me — the fact that there were symmetries, like parity conservation, charge conjugation invariance, and strangeness conservation, that were very good symmetries of the strong and electromagnetic interactions — as far as we knew exact — and yet were not respected by the weak interactions. Why should nature have ... symmetries that are symmetries of part of nature but not other parts of nature?
- "Reminiscences of the Standard Model" - Special Colloquium by Steven Weinberg, 17 October 2017, YouTube video at 1:02:17 of 1:39:24
- ... I found that I was unable to explain the foundations of quantum mechanics in a way that I found entirely satisfactory.
- The Problems of Quantum Mechanics: Steven Weinberg (July 17, 2018) YouTube video at 3:58 of 45:42
- In the Standard Model the masses of quarks and leptons take values proportional to the coupling constants in the interaction of these fermions with scalar fields, constants that in the context of this model are entirely arbitrary. But the peculiar hierarchical pattern of lepton and quark masses seems to call for a larger theory, in which in some leading approximation the only quarks and leptons with non-zero mass are those of the third generation, the tau, top, and bottom, with the other lepton and quark masses arising from some sort of radiative correction. Such theories were actively considered ... soon after the completion of the Standard Model, but interest in this program seems to have lapsed subsequently ...
- (2020). "Models of lepton and quark masses". Physical Review D 101 (3). DOI:10.1103/PhysRevD.101.035020.
- ... there are particles ... that we have never seen in a laboratory but astronomers tell us make up most of the matter in the universe — the so-called dark matter. It's dark because it doesn't radiate — it doesn't interact with light. We just know about it because of its gravitational field. What is the dark matter? ... We have a lot of ideas — all going in different directions. We don't know which is the right idea.
- Steven Weinberg Final Interview. Knowing Science® Registered Trademark, YouTube (August 20, 2021). (quote at 7:54 of 15:51; interview by William Banko)
The First Three Minutes (1977; second edition 1993)Edit
- Our mistake is not that we take our theories too seriously, but that we do not take them seriously enough. It is always hard to realize that these numbers and equations we play with at our desks have something to do with the real world. ...The most important thing accomplished by the three-degree radiation background in 1965 was to force us to take seriously the idea that there was an early universe.
- It is almost irresistible for humans to believe that we have some special relation to the universe, that human life is not just a more-or-less farcical outcome of a chain of accidents reaching back to the first three minutes, but that we were somehow built in from the beginning. ... It is very hard to realise that this is all just a tiny part of an overwhelmingly hostile universe. It is even harder to realise that this present universe has evolved from an unspeakably unfamiliar early condition, and faces a future extinction of endless cold or intolerable heat. The more the universe seems comprehensible, the more it also seems pointless.
- (1993), Epilogue, p. 154
- The effort to understand the universe is one of the very few things which lifts human life a little above the level of farce and gives it some of the grace of tragedy.
- (1993), Epilogue, p. 155
Dreams of a Final Theory (1992; 2nd edition 1994)Edit
- The years since the mid-1970s have been the most frustrating in the history of particle physics. We are paying the price of our own success: theory has advanced so far that further progress will require the study of processes at energies far beyond the reach of existing facilities. In order to break out of this impasse, physicists began in 1982 to develop plans for a scientific project of unprecedented size and cost, known as the Superconducting Super Collider.
- It is with Isaac Newton that the modern dream of a final theory really begins.
- The last thirty years of Einstein's life were largely devoted to a search for a so-called unified field theory that would unify James Clerk Maxwell's theory of electromagnetism with the general theory of relativity, Einstein's theory of gravitation. Einstein's attempt was not successful, and with hindsight we can now see that it was misconceived. Not only did Einstein reject quantum mechanics; the scope of his effort was too narrow. ... Nevertheless Einstein's struggle is our struggle today. It is the search for a final theory.
- The best military historians in fact do recognize the difficulty in stating rules of generalship. They do not speak of a science of war, but rather of a pattern of military behavior that cannot be taught or stated precisely but that somehow or other sometimes helps in winning battles. This is called the art of war. In the same spirit I think that one should not hope for a science of science, the formulation of any definite rules about how scientists do or ought to behave, but only aim at a description of the sort of behavior that historically has led to scientific progress—an art of science.
- Chap. 5 : Tales of Theory and Experiment
Scientist: Four golden lessons (2003)Edit
"Scientist: Four golden lessons", Nature (27 November 2003)
- I managed to get a quick PhD — though when I got it I knew almost nothing about physics. But I did learn one big thing: that no one knows everything, and you don't have to.
- Another lesson to be learned, to continue using my oceanographic metaphor, is that while you are swimming and not sinking you should aim for rough water.
- As you will never be sure which are the right problems to work on, most of the time that you spend in the laboratory or at your desk will be wasted. If you want to be creative, then you will have to get used to spending most of your time not being creative, to being becalmed on the ocean of scientific knowledge.
- Finally, learn something about the history of science, or at a minimum the history of your own branch of science. The least important reason for this is that the history may actually be of some use to you in your own scientific work.
The Atheism Tapes (2004)Edit
- Interview in 2003, broadcast as Episode 2
- Many people do simply awful things out of sincere religious belief, not using religion as a cover the way that Saddam Hussein may have done, but really because they believe that this is what God wants them to do, going all the way back to Abraham being willing to sacrifice Isaac because God told him to do that. Putting God ahead of humanity is a terrible thing.
- Maybe at the very bottom of it... I really don't like God. You know, it's silly to say I don't like God because I don't believe in God, but in the same sense that I don't like Iago, or the Reverend Slope or any of the other villains of literature, the god of traditional Judaism and Christianity and Islam seems to me a terrible character. He's a god who will... who obsessed the degree to which people worship him and anxious to punish with the most awful torments those who don't worship him in the right way. Now I realise that many people don't believe in that any more who call themselves Muslims or Jews or Christians, but that is the traditional God and he's a terrible character. I don't like him.
- I have a friend — or had a friend, now dead — Abdus Salam, a very devout Muslim, who was trying to bring science into the universities in the Gulf states and he told me that he had a terrible time because, although they were very receptive to technology, they felt that science would be a corrosive to religious belief, and they were worried about it... and damn it, I think they were right. It is corrosive of religious belief, and it's a good thing too.
- There is one constant that seems to be fine tuned...and that is dark energy.
- I'm offended by the kind of smarmy religiosity that's all around us, perhaps more in America than in Europe, and not really that harmful because it's not really that intense or even that serious, but just... you know after a while you get tired of hearing clergymen giving the invocation at various public celebrations and you feel, haven't we outgrown all this? Do we have to listen to this?
Lectures on Quantum Mechanics (2012, 2nd ed. 2015)Edit
- The development of quantum mechanics in the 1920s was the greatest advance in physical science since the work of Isaac Newton. It was not easy; the ideas of quantum mechanics present a profound departure from ordinary human intuition. Quantum mechanics has won acceptance through its success. It is essential to modern atomic, molecular, nuclear, and elementary particle physics, and to a great deal of chemistry and condensed matter physics as well.
- The principles of quantum mechanics are so contrary to ordinary intuition that they can best be motivated by taking a look at their prehistory.
- Ch. 1: Historical Introduction
- Perhaps the most important immediate consequence of Planck’s work was to provide long-sought values for atomic constants.
- Ch. 1: Historical Introduction
- Planck’s quantization assumption applied to the matter that emits and absorbs radiation, not to radiation itself. As George Gamow later remarked, Planck thought that radiation was like butter; butter itself comes in any quantity, but it can be bought and sold only in multiples of one quarter pound. It was Albert Einstein (1879–1955) who in 1905 proposed that the energy of radiation of frequency ν was itself an integer multiple of hν.
- Ch. 1: Historical Introduction
- In this derivation Bohr had relied on the old idea of classical radiation theory, that the frequencies of spectral lines should agree with the frequency of the electron’s orbital motion, but he had assumed this only for the largest orbits, with large n. The light frequencies he calculated for transitions between lower states, such as n=2 → n=1, did not at all agree with the orbital frequency of the initial or final state. So Bohr’s work represented another large step away from classical physics.
- Ch. 1: Historical Introduction
- Heisenberg’s starting point was the philosophical judgment, that a physical theory should not concern itself with things like electron orbits in atoms that can never be observed. This is a risky assumption, but in this case it served Heisenberg well.
- Ch. 1: Historical Introduction
- To start, we will consider a single particle moving in three space dimensions under the influence of a general central potential. Later we will specialize to the case of a Coulomb potential, and work out the spectrum of hydrogen. One other classic problem, the harmonic oscillator, will be treated at the end of this chapter.
- Ch. 2: Particle States in a Central Potential
- My own conclusion is that today there is no interpretation of quantum mechanics that does not have serious flaws. This view is not universally shared. Indeed, many physicists are satisfied with their own interpretation of quantum mechanics. But different physicists are satisfied with different interpretations. In my view, we ought to take seriously the possibility of finding some more satisfactory other theory, to which quantum mechanics is only a good approximation.
- Ch. 3: General Principles of Quantum Mechanics
Quotes about WeinbergEdit
- Steven Weinberg is famous as a scientist, but he thinks deeply and writes elegantly about many other things besides science.… he is not only preeminent as a mathematical physicist. He has also made important contributions to the discussion of history and politics.
- Freeman Dyson, ‘What Price Glory?’, The New York Review of Books (June 10, 2010)
- Asked what single mystery, if he could choose, he would like to see solved in his lifetime, Weinberg doesn’t have to think for long: he wants to be able to explain the observed pattern of quark and lepton masses.
- Matthew Chalmers from an interview: (13 October 2017)"Model physicist". CERN Courier.
- Weinberg’s paper “A Model of Leptons”, published in Physical Review Letters (PRL) on 20 November 1967, determined the direction of high-energy particle physics through the final decades of the 20th century. Just two and a half pages long, it is one of the most highly cited papers in the history of theoretical physics. Its contents are the core of the Standard Model of particles physics, now almost half a century old and still passing every experimental test.
- Frank Close in: (13 October 2017)"Birth of a symmetry". CERN Courier.
- Here he unwittingly puts his finger on what I believe is the actual source of the near-century of discomfort and disagreement. There is an implicit assumption, shared by almost all physicists, that the scientist must be separated from the science. The usual appeals to measurement with classical outcomes, it seems to me, are unsuccessful attempts to objectify and impersonalize processes in which an individual scientist acts on and is reacted upon by the world. The collapse of the wavefunction after measurement represents nothing more than the updating of that scientist’s expectations, based on his or her experience of the world’s response to the measurement. Weinberg hopes to keep the scientist out of the laws of nature, but our chronic failure to agree on the meaning of quantum mechanics demonstrates the futility of his hope.
Nor does Weinberg’s hope make sense to me. Science is a highly developed form of human language. Embedded in books and papers, it is a distillation of the communicated individual experiences of all scientists. Why insist that science should make no reference to the process that has established it? The laws of quantum mechanics are exactly the same for everyone who uses them. In that important sense they are entirely objective. If a scientific law involves both the scientist and the world, it does not mean that science can tell us nothing about people, as Weinberg mysteriously worries, any more than it means that science can tell us nothing about the world.
- N. David Mermin, "Can the scientist play a role in the laws of physics?", Physics Today (01 January 2019)
- By inclination, Weinberg is an extreme reductionist. But he is also a realist and acknowledges when something is not working the way he might want it to. In 1987 the arch-reductionist concluded that certain facts seemed to be inconsistent with any explanation based on the usual kind of mathematical reasoning. Instead, it seemed they might be true only because if they were not, we observers could not be here to observe them. Weinberg undoubtedly disliked such anthropic-principle explanations. But when, to his disappointment, he found that the anthropic principle might explain the apparent vanishing of the cosmological constant, he said so loudly and clearly, despite the great hostility of the physics community toward the principle.
- Leonard Susskind: (2010). "Review of Lake Views: This World and the Universe by Steven Weinberg". Physics Today 63 (4): 53. DOI:10.1063/1.3397044.
- ... I vividly remember sitting in front of Wheeler, who told me his opinion of the leading particle theorists at various major universities and ended with the pronouncement that Steve Weinberg was the best of the upcoming generation.
- Anthony Zee: (2009). "A life shaped by John Wheeler". Physics Today 62 (10): 10–12. ISSN 0031-9228. DOI:10.1063/1.3248449.