Quotes from The Character of Physical Law

“Mathematics is a language plus reasoning; it is like a language plus logic. Mathematics is a tool for reasoning.”
― Richard Feynman, quote from The Character of Physical Law

“... it is impossible to explain honestly the beauties of the laws of nature in a way that people can feel, without their having some deep understanding of mathematics. I am sorry, but this seems to be the case.”
― Richard Feynman, quote from The Character of Physical Law

“In fact the total amount that a physicist knows is very little. He has only to remember the rules to get him from one place to another and he is all right...”
― Richard Feynman, quote from The Character of Physical Law

“For those who want some proof that physicists are human, the proof is in the idiocy of all the different units which they use for measuring energy.”
― Richard Feynman, quote from The Character of Physical Law

“I am going to tell you what nature behaves like. If you will simply admit that maybe she does behave like this, you will find her a delightful, entrancing thing. Do not keep saying to yourself, if you can possibly avoid it, ‘But how can it be like that?’ because you will get ‘down the drain’, into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that.”
― Richard Feynman, quote from The Character of Physical Law

“Electrons, when they were first discovered, behaved exactly like particles or bullets, very simply. Further research showed, from electron diffraction experiments for example, that they behaved like waves. As time went on there was a growing confusion about how these things really behaved ---- waves or particles, particles or waves? Everything looked like both.

This growing confusion was resolved in 1925 or 1926 with the advent of the correct equations for quantum mechanics. Now we know how the electrons and light behave. But what can I call it? If I say they behave like particles I give the wrong impression; also if I say they behave like waves. They behave in their own inimitable way, which technically could be called a quantum mechanical way. They behave in a way that is like nothing that you have seen before. Your experience with things that you have seen before is incomplete. The behavior of things on a very tiny scale is simply different. An atom does not behave like a weight hanging on a spring and oscillating. Nor does it behave like a miniature representation of the solar system with little planets going around in orbits. Nor does it appear to be somewhat like a cloud or fog of some sort surrounding the nucleus. It behaves like nothing you have seen before.

There is one simplication at least. Electrons behave in this respect in exactly the same way as photons; they are both screwy, but in exactly in the same way….

The difficulty really is psychological and exists in the perpetual torment that results from your saying to yourself, "But how can it be like that?" which is a reflection of uncontrolled but utterly vain desire to see it in terms of something familiar. I will not describe it in terms of an analogy with something familiar; I will simply describe it. There was a time when the newspapers said that only twelve men understood the theory of relativity. I do not believe there ever was such a time. There might have been a time when only one man did, because he was the only guy who caught on, before he wrote his paper. But after people read the paper a lot of people understood the theory of relativity in some way or other, certainly more than twelve. On the other hand, I think I can safely say that nobody understands quantum mechanics. So do not take the lecture too seriously, feeling that you really have to understand in terms of some model what I am going to describe, but just relax and enjoy it. I am going to tell you what nature behaves like. If you will simply admit that maybe she does behave like this, you will find her a delightful, entrancing thing. Do not keep saying to yourself, if you can possible avoid it, "But how can it be like that?" because you will get 'down the drain', into a blind alley from which nobody has escaped. Nobody knows how it can be like that.”
― Richard Feynman, quote from The Character of Physical Law

“I happen to know this, and I happen to know that, and maybe I know that;and I work everything out from there. Tomorrow I may forgot that this is true, but remember that something else is true, so I can reconstruct it all again. I am never quite sure of where I am supposed to begin or where I am supposed to end. I just remember enough all the time so that as the memory fades and some of the pieces fall out I can put the thing back together again every day”
― Richard Feynman, quote from The Character of Physical Law

“It is absurd that energy can be measured in calories, in ergs, in electron volts, in foot pounds, in B.T.U.s, in horsepower hours, in kilowatt hours–all measuring exactly the same thing. It is like having money in dollars, pounds, and so on; but unlike the economic situation where the ratio can change, these dopey things are in absolutely guaranteed proportion. If”
― Richard Feynman, quote from The Character of Physical Law

“You might say that the only reason for the anti-neutrino is to make the conservation of energy right. But it makes a lot of other things right, like the conservation of momentum and other conservation laws, and very recently it has been directly demonstrated that such neutrinos do indeed exist.”
― Richard Feynman, quote from The Character of Physical Law

“This example illustrates a point. How is it possible that we can extend our laws into regions we are not sure about? Why are we so confident that, because we have checked the energy conservation here, when we get a new phenomenon we can say it has to satisfy the law of conservation of energy ?”
― Richard Feynman, quote from The Character of Physical Law

“For instance, the mass of an object changes when it moves, because of the conservation of energy. Because of the relation of mass and energy the energy associated with the motion appears as an extra mass, so things get heavier when they move. Newton”
― Richard Feynman, quote from The Character of Physical Law

“angular momentum appears in two forms : one of them is angular momentum of motion, and the other is angular momentum in electric and magnetic fields. There is angular momentum in the field around the magnet, although it does not appear as motion, and this has the opposite sign to the spin. If”
― Richard Feynman, quote from The Character of Physical Law

“There are other conservation laws. They are not as interesting as those I have described, and do not deal exactly with the conservation of numbers. Suppose”
― Richard Feynman, quote from The Character of Physical Law

“Suppose we had some kind of device with particles moving with a certain definite symmetry, and suppose their movements were bilaterally symmetrical (fig. 20). Then, following the laws of physics, with all the movements and collisions, you could expect, and rightly, that if you look at the same picture later on it will still be bilaterally symmetrical. So there is a kind of conservation, the conservation of the symmetry character. This should be in the table, but it is not like a number that you measure, and we will discuss it in much more detail in the next lecture. The reason this is not very interesting in classical physics is because the times when there are such nicely symmetrical initial conditions are very rare, and it is therefore a not very important or practical conservation law. But”
― Richard Feynman, quote from The Character of Physical Law

“This is how a rocket works. At first it is standing still, say, in empty space, and then it shoots some gas out of the back, and the rocket goes forward. The point is that of all the stuff in the world, the centre of mass, the average of all the mass, is still right where it was before. The interesting part has moved on, and an uninteresting part that we do not care about has moved back. There”
― Richard Feynman, quote from The Character of Physical Law

“Discovering the laws of physics is like trying to put together the pieces of a jigsaw puzzle. We”
― Richard Feynman, quote from The Character of Physical Law

“Professor Weyl,* the mathematician, gave an excellent definition of symmetry, which is that a thing is symmetrical if there is something that you can do to it so that after you have finished doing it it looks the same as it did before. That is the sense in which we say that the laws of physics are symmetrical; that there are things we can do to the physical laws, or to our way of representing the physical laws, which make no difference, and leave everything unchanged in its effects. It is this aspect of physical laws that is going to concern us in this lecture.”
― Richard Feynman, quote from The Character of Physical Law

“Einstein realized, and Poincaré* too, that the only possible way in which a person moving and a person standing still could measure the speed to be the same was that their sense of time and their sense of space are not the same, that the clocks inside the space ship are ticking at a different speed from those on the ground, and so forth. You”
― Richard Feynman, quote from The Character of Physical Law

“The symmetries of translation in space, delay in time, and so on, were not very deep; but the symmetry of uniform velocity in a straight line is very interesting, and has all kinds of consequences. Furthermore, these consequences are extendable into laws that we do not know. For example, by guessing that this principle is true for the disintegration of a mu meson, we can state that we cannot use mu mesons to tell how fast we are going in a space ship either; and thus we know something at least about mu meson disintegration, even though we do not know why the mu meson disintegrates in the first place.”
― Richard Feynman, quote from The Character of Physical Law

“Of all the conservation laws, that dealing with energy is the most difficult and abstract, and yet the most useful. It”
― Richard Feynman, quote from The Character of Physical Law

“By this time you are probably convinced that all the laws of physics are symmetrical under any kind of change whatsoever, so now I will give a few that do not work. The first one is change of scale. It is not true that if you build an apparatus, and then build another one, with every part made exactly the same, of the same kind of stuff, but twice as big, that it will work in exactly the same way. You”
― Richard Feynman, quote from The Character of Physical Law

“The conservation of energy is a little more difficult, because this time we have a number which is not changed in time, but this number does not represent any particular thing. I”
― Richard Feynman, quote from The Character of Physical Law

“The little cathedral made with matchsticks is attracted to the earth, so to make a comparison the big cathedral should be attracted to an even bigger earth. Too bad. A bigger earth would attract it even more, and the sticks would break even more surely!”
― Richard Feynman, quote from The Character of Physical Law

“I suppose Galileo felt that the discovery of the fact that the laws of nature are not unchanged under change of scale was as important as his laws of motion, because they are both put together in the tome on Two New Sciences.”
― Richard Feynman, quote from The Character of Physical Law

“All physics is rooted in the notion of law, the belief that we live in an ordered universe that can be understood by the application of rational reasoning. But”
― Richard Feynman, quote from The Character of Physical Law

“There is also a rhythm and a pattern between the phenomena of nature which is not apparent to the eye, but only to the eye of analysis; and it is these rhythms and patterns which we call Physical Laws. What”
― Richard Feynman, quote from The Character of Physical Law

“But the motion to keep the planet going in a straight line has no known reason. The reason why things coast for ever has never been found out. The law of inertia has no known origin. Although”
― Richard Feynman, quote from The Character of Physical Law

“With energy there is this difference, that there are no blocks, so far as we can tell. Also, unlike the case of the blocks, for energy the numbers that come out are not integers. I”
― Richard Feynman, quote from The Character of Physical Law

“Conservation just means that it does not change.”
― Richard Feynman, quote from The Character of Physical Law

“When we add all the numbers together, from all the different forms of energy, it always gives the same total. But as far as we know there are no real units, no little ballbearings. It”
― Richard Feynman, quote from The Character of Physical Law

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