Quotes from The Character of Physical Law

The next question was - what makes planets go around the sun? At the time of Kepler some people answered this problem by saying that there were angels behind them beating their wings and pushing the planets around an orbit. As you will see, the answer is not very far from the truth. The only difference is that the angels sit in a different direction and push their wings inwards. (page 18)

Today our theories of phyics, the laws of physics, are a multitude of different parts and pieces that do not fit together very well. We do not have one structure from which all is deduced; we have several pieces that do not quite fit exactly yet. ... But what is very strange is that there are certain things which are the same in both [gravity and electricity]. (page 30)

But the most impressive fact is that gravity is simple. It is simple to state the principles completely and not have left any vagueness for anybody to change the ideas of the law. It is simple, and therefore it is beautiful. I do not mean it is simple in its action - the motions of the various planets and the perturbations of one on the other can be quite complicated to work out ... but the basic pattern or the system beneath the whole thing is simple. This is common to all our laws; they all turn out to be simple things, although complex in their actual actions. (page 33-34)

What does the planet do? Does it look at the sun, see how far away it is, and decide to calculuate on its internal adding machine the inverse of the distance, which tells it how much to move? This is certainly no explanation of the machinery of gravitation! ... [Newton] said, 'It tells you how it moves. That should be enough. I have told you how it moves, not why.' (page 37)

Every one of our laws is a purely mathematical statement in rather complex and abstruse mathematics ... It gets more and more difficult as we go on. Why? I have not the slightest idea. (page 39)

Mathematics is just organized reasoning (page 41)

Now we have a problem. We can deduce from one part of physics, like the Law of Gravititation, a principle which turns out to be more valid that the derivation ... Newton had other postulates by which he could get the more general conservation law of angular momentum. But these Newtonian laws were wrong. There are no forces, it is all a lot of boloney, the particles do not have orbits, and so on. Yet the analogue, the exact transformation of this principle about the areas and the conservation of angular momentum, is true. It works for atomic motions in quantum mechanics, and, as far as we can tell, it is still exact today. (page 49)

Physics is not mathematics, and mathematics is not physics. One helps the other. But in physics you have an understanding of the connection of words with the real world. (page 55)

I really think that those two cultures [those of C.P. Snow] separate people who have and people who have not had this experience of understanding mathematics well enough to appreciate nature once. It is too bad that it has to be mathematics, and that mathematics is hard for some people ... If you want to learn about nature, to appreciate nature, it is necessary to understand the language that she speaks in. (page 58)

In order to avoid simply describing experiments that have been done, we have to propose laws beyond their observed range. There is nothing wrong with that, despite the fact that it makes science uncertain. If you thought before that science was certain - well, that is just an error on your part. (page 77)

How do we know that [the laws of physics] belong together? How do we know that they are really part of one as yet incomplete picture? We are not sure, and it worries us to some extenet, but we get encouragement from the common characteristics of several pieces. They all show blue sky, or the are all made out of the same kind of wood. All the various physical laws obey the same conservation principles. (page 83)

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 look the same as it did before. (page 84)

As time went on, new laws were discovered after Newton, among them the laws of electricity discovered by Maxwell. One of the consequences of the laws of electricity was that there should be waves, electromagnetic waves - light is an example - which should go at 186,000 miles a second, flat ... So it was easy to tell where rest was, because the law that light goes at 186,000 miles a second is certainly not (at first sight) one which will permit one to move without some effect. (page 91)

A generalization of the two-dimensional rotation that I spoke about was therefore made into space and time, so that time was added to space to make a four-dimensional world. It is not merely and artificial addition ... Real space has, in a sense, the characteristic that its existence is independent of the particular point of view, and that looked at from different points of view a certain amount of 'forward-backward' can get mixed up with 'left-right'. In an analogous way a certain amount of time 'future-past' can get mixed up with a certain amount of space. Space and time must be completely interlocked (page 93-94)

The thing that is interesting is that if you measure the spin - electrons are spinning as they come out - you find that they are spinning to the left ... It is as though in the beta decay the gun that was shooting out the electron were a rifled gun ... Therefore it is possible to tell right from left, and thus the law that the world is symmetrical for left and right has collapsed. (page 103)

Things are irreversible only in a sense that going one way is likely, but going the other way, although it is possible and is according to the laws of physics, would not happen in a million years. (page 112)

To stand at either end, and to walk off that end of the pier only, hoping that out in that direction is the complete understanding, is a mistake. And to stand with evil and beauty and hope, or to stand with the fundamental laws, hoping that way to get a deep understanding of the whole world, with that aspect alone, is a mistake ... The great mass of workers in between, connecting one step to another, are improving all the time our understanding of the world, both from working at the ends and working in the middle, and in that way we are gradually understanding this tremendous world of interconnecting hierarchies. (page 126-127)

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 ... On the other hand, I think I can safely say that nobody understands quantum mechanics ... Do not keep saying to yourself, if you can possibly avoid it, 'But how can it be like that?' ... Nobody knows how it can be like that. (page 129)

Of course we are not averse to using the theory of probability, that is calculating odds, when a situation is very complicated ... But here what we are proposing, is it not, is that there is probability all the way back: that in the fundamental laws of physics there are odds. (page 145)

In general we look for a new law by the following process. First we guess it. Then we compute the consequences of the guess to see what would be implied if this law that we guessed is right. Then we compare the result of the computation to nature, with experiment or experience, compare it directly with observation, to see if it works. If it disagress with experiment it is wrong. In that simple statement is the key to science. It does not make any difference how beautiful your guess is. It does not make any difference how smart you are, who made the guess, or what his name is - if it disagrees with experiment it is wrong. (page 156)

Suppose you invent a good guess, calculate the consequences, and discover every time that the consequences you have calculated agree with experiment. The theory is then right? No, it is simply not proved wrong ... We never are definitely right, we can only be sure we are wrong. (page 158)

We must, and we should, and we always do, extend as far as we can beyond what we already know, beyond those ideas that we have already obtained. Dangerous? Yes. Uncertain? Yes. But it is the only way to make progress. Although it is uncertain, it is necessary to make science useful. Science is only useful if it tells you about some experiment that has not been done; it is no good if it only tells you what just went on. (page 164)

It is not unscientific to make a guess, although many people who are not in science think it is. (page 165)

Then there is another school of thought, which has only one representative, myself, which says no, the thing may be complicated and become simple only through the complications. The Greeks believed that the orbits of the planets were circles. Actually they are ellipses. They are not quite symmetrical, but they are very close to circles. Why are they nearly symmetrical? Because of a long complicated effect of tidal friction - a very complicated idea. (page 167)

It seems to me that what can happen in the future is either that all the laws become known ... or it may happen that the experiments get harder and harder to make, more and more expensive, so you get 99.9 percent of the phenomena, but there is always some phenomenon which has just been discovered, which is very hard to measure, and which disagrees; and as soon as you have the explanation of that one there is always another one, and it gets slower and slower and more and more uninteresting. That is another way it may end. (page 172)

What is it about nature that lets this happen, that it is possible to guess from one part what the rest is going to do? That is an unscientific question: I do not know how to answer it, and therefore I am going to give an unscientific answer. I think it is because nature has a simplicity and therefore a great beauty. (page 173)