Steven Weinberg

"As a special case of Newton's Second Law, a body... when acted on by zero force, will experience zero acceleration—that is, it will move with constant velocity. Newton listed this... as the First Law... The Third Law... action equals reaction: If one body exerts a force on another... the second... exerts an equal force in the opposite direction on the first."

"When the velocity and the acceleration are changing, we can define the instantaneous velocity or acceleration at any moment as the average values... over a vanishingly small time interval centered on that moment. Newton's Law actually relates the force to the instantaneous acceleration."

"Thomson... exerted electric and magnetic forces on the rays and measured the amount... deflected."

"Acceleration is the rate of change of . ...The units are ...velocity per unit time, or distance-per-time per time. ...[F]alling bodies ...near ...earth fall with an acceleration or 9.8 meters-per-second per second ...after the first second ...falling at speed ...9.8 meters per second, after two seconds... 19.6 ...and so on. [T]he units of velocity are length/time... and units of acceleration... (distance/time)/time, or equivalently distance/time2 ...[T]he acceleration near... Earth would be written 9.8 m/sec2 for short."

"The laws of motion... were set out by... Newton at the beginning of... the Principia. ...[T]he key principle is ...in the Second Law... paraphrased as... the force to give an object a certain acceleration is proportional to the product of the and the ."

"... most physicists would probably agree that the place of local fields is nowhere so secure as in 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."

"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."

"Elementary particles are terribly boring, which is one reason why we're so interested in them."

"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."

"The more the universe seems comprehensible, the more it also seems pointless."

"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."

"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."

"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."

"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."

"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."

"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."

"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."

"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."

"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."

"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."

"There is a hope, which I nurse but I don't see being realized, that eventually we'll find that quantum mechanics as we know it now is just an approximation ..."

"'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 . And I mentioned this to Mrs. Källén and she said they were a present from Pauli."

"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."

"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?"

"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."

"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."

"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."

"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?"

"... I found that I was unable to explain the foundations of quantum mechanics in a way that I found entirely satisfactory."

"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 ..."

"... 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 . 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."

"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."

"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."

"This book is written for readers who may not be familiar with classical physics, but who are willing to pick up enough... to be able to understand the rich tangle of ideas and experiments that make up the history of twentieth century physics. This background is provided in a number of "flashback"sections on the nature of electricity, Newton's laws of motion, electric and magnetic forces, conservation of energy, atomic weights and so on... inserted wherever... needed to allow the reader to understand the next point in the history. ...Generally ...the student or reader is ...is offered only one path ...ideal for ...physicists, but for many ...an impassable desert ...I invite the reader to plunge immediately into... key topics ...using each ...as an entreé into just those concepts and methods ...needed to understand that topic. ...Most of what I know about physics and mathematics I have learned only when there was no alternative ...in order to get on with my work. ...So the plan of this book may be closer to the actual education of working scientists than many ...My hope ...that this book may contribute to a radical revision in the way ...science is brought to the nonscientists. ...This book is intended to be comprehensible to readers who have no prior background in science, and no familiarity with mathematics beyond arithmetic. ...Appendices present some of the calculations that underlie the reasoning in the main text. ...The great scientific achievements described here form the a large part of the soil from which our... recent harvest of discoveries have sprung. ...I hope that scientists find some ...enlightening. I also hope that this book will be enjoyed by students and practitioners of the history of science."

"This is not intended to be yet another popular book that offers... the latest news in physics. Still, it would be a pity not to show the links between the historic discoveries... and the work of fundamental physics today. I have therefore taken the opportunity... of this new edition to point out these links... I now carry the story of the discovery of elementary particles... to the present day."

"By the end of the nineteenth century the idea of the atom had become familiar... but not yet universally accepted. Partly because of the heritage of Newton and Dalton, there was a disposition to use atomic theories in England. ...Resistance to atomism persisted in Germany ...under the influence of an empiricist school... centered on Ernst Mach... many [German physicists and chemists] held back from incorporating into... theories anything that—like atoms—could not be observed directly. ...It is said that the opposition to Boltzmann's work by the followers of Mach contributed to Boltzmann's suicide..."

"Under ordinary circumstances, visible light is absorbed or emitted when the electrons in an atom or molecule are excited into orbits of higher energy, or sink back into orbits of lower energy, respectively."

"The s and s in nuclei, like the electrons surrounding the nuclei, can be excited to states of higher energy or... fall back to a state of lower energy, but the energies... are typically a million times those need to excite the electrons..."

"Electrons are believed to be absolutely stable, and protons and neutrons (when bound...) live at least 1030 years. With few exceptions, all other particles have very short lifetimes..."

"The reader may... wonder why when amber is rubbed with fur the electrons go from the fur to the amber, but when glass is rubbed with silk the electrons go from the glass to the silk? ...[W]e still don't know. The question involves the physics of surfaces of complex solids... In a purely empirical way, there has been developed... the triboelectric sequence... The electrification is most intense for objects... well separated in the... sequence. ...It is ironic that we still do not have a detailed understanding of frictional electrification, even though it was the first... to be studied... But... often... science progresses... by selecting problems that are as free as possible from irrelevant complications and... provide opportunities to get at fundamental principles..."

"In 1709 Hauksbee observed that when air inside a glass vessel was evacuated... [to] 1/60 normal air pressure and the vessel was attached to... frictional electricity, a strange light would be seen... Flashes... similar... had... been noticed in the partial vacuum above... mercury in barometers. ...[T]oday we know ...[w]hen an electric current flows through a gas, the electrons knock into the gas atoms and give up some... energy... reemitted as as light. Today's fluorescent lights and neon signs are based on the same principle... but even at 1/60 atmospheric pressure the air interfered too much with the flow of electrons to allow their nature to be discovered. Real progress became possible only when the gas... could be removed..."

"In 1858 Johann Heinrich Geissler... invented a pump that used columns of mercury as pistons and consequently needed no gaskets. ...Geissler's pump was used... by ... [M]etal plates inside a glass tube were connected to a powerful source of electricity. ...[W]hen almost all of the air was evacuated ...the light disappeared through most of the tube, but a greenish glow appeared ...near the cathode. ...A few years later, ... introduced a name... s. We know now that these rays are streams of electrons. ...But this was far from obvious to nineteenth century physicists. ...Plücker ...observed that the position of the glow on the walls of the tube could be moved by ...a magnet ..."

"Plücker's student J. W. Hittorf... observed that solid bodies... near a small cathode would cast shadows... [and] deduced... the rays travel... in straight lines."

"Hertz showed... the... rays were not appreciably deflected by electrified metal plates. This seemed to rule out... electrically charged particles... Hertz concluded the rays were some sort of wave... the nature of light was... not well understood, and a magnetic deflection did not seem impossible. In 1891 Hertz made a further observation... to support the wave theory... The rays could penetrate thin foils of gold and other metals, much as light penetrates glass. ...We know now that... the... particles were traveling so fast, and the electric forces were so weak... the deflection was too small to observe."

"Perrin... showed in 1895 that the rays deposit negative electrical charge on a charge collector... inside... the tube."

"[I]n 1897 Thomson... detected a deflection... by electric forces between the rays and the electrified metal plates. ...due largely to the use of better vacuum pumps ...to where the effects of residual gas ...became negligible. (Some evidence for... deflection was [also] found... by Goldstein.) [D]eflection was toward the positively charged plate... away from the negatively charged one, confirming Perrin... that the rays carry negative electric charge."

"Velocity, acceleration, and force are vectors... they have direction as well as magnitude. It is often convenient to describe... [vectors] in terms of their components along specified directions. ...Components of vectors can be negative as well as positive ...Newton's Second Law applies separately to each component... it says... the component of force in any direction is equal to the mass times the corresponding component of acceleration."