The Character of Physical Law

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First edition.

The Character of Physical Law is a book adaptation of a series of introductory physics lectures given by Richard Feynman for the Cornell Messenger Lectures in November, 1964. The book was first published in 1965. The lectures explain a variety of physical models, and discusses how physicists work to think up, test, and refine these models.


After a stint of bad sci-fi novels, I looked for a non-fiction book to cleanse my palette, and this one intrigued me. I finished it on 2022-02-09.


I don't own this book, but have listened to the audio book read by Sean Runnette.



  • Despite all their success, Feynman is quick to point out how much physicists still don't know about the universe and just how much their understanding is based on guess work. I'm always impressed with his humility.
  • I found the section on gravity, where he explains that there are currently three very different explanations of gravity, but each is still a very accurate, to be really eye-opening. It reminds us that we can get correct results but still have a very wrong model of something in our head. He uses a similar example to explain why it's so hard to replace an existing straightforward model with an obtuse model. The Mayan calendar could predict eclipses with high accuracy, but the Mayan's didn't understand celestial objects to orbit and used linear arithmetic rather than geometry to get their results. So, to suggest a model where the objects orbit would feel strange and not yield accurate results at first, even though it would be vastly more correct.
  • The analogy of a mother trying to find blocks that were hidden by a child in a room, and she can only find them indirectly using math is a great way to explain the complexities of finding missing energy when trying to prove the law of the conservation of energy.
  • Over all, Feynman is very excited about physics, and optimistic for the future of the field, which makes his lectures very enjoyable.


  • Feynman anthropomorphizes nature too much; it isn't a "she", it doesn't "want" to do things, etc. Also, he invokes a generic "god" which always gives the wrong impression to religious people.
  • As is typical with experts speaking to amateurs, Feynman sometimes uses jargon without explaining it. Not a lot, but enough to prevent comprehension of certain topics.
  • When Feynman goes outside of his wheelhouse, like when he explains how historians answer questions, he's quite unreliable.
  • The audio book has some problems: Feynman used many illustrations in his lectures which the audio book doesn't even attempt to describe (although a later version includes them). Also, the reader has a slight lisp which I sometimes found distracting.


  • Nothing.




The complete lecture series.


  • "In general, we look for a new law by the following process: First we guess it. Then we – now don't laugh, that's really true. Then we compute the consequences of the guess to see what, if this is right, if this law that we guessed is right, to see what it would imply. And then we compare the computation results to nature, or we say compare to experiment or experience, compare it directly with observations to see if it works. If it disagrees with experiment, it's wrong. In that simple statement is the key to science. It doesn't make any difference how beautiful your guess is, it doesn't make any difference how smart you are, who made the guess, or what his name is. If it disagrees with experiment, it's wrong. That's all there is to it."
  • "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 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."
  • "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."
  • "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."


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