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I think that the Feynman Lectures are a great, in some ways unique resource for both physics students and working physicists. They’ve held up remarkably well in most respects, despite being now over fifty years old. But I think that they’re best used as a complement to more standard and modern textbooks, rather than as the primary source of information on the many subjects that they cover. If you set out to learn physics from the beginning by relying principally on the Feynman Lectures you might be disappointed and confused after a while. (There’s no royal road to physics, as Euclid said about geometry to the King of Egypt.)
I’ve noticed that some people, here on Quora and elsewhere, complain that the lectures are “too wordy” and that they’d prefer something more “rigorous”. I think that their problem is not with the mathematical rigor, but with the style of the presentation. The way the lectures went is that Feynman arrived at class with some sketchy notes and proceeded to improvise from them, as any professor might when teaching something for the first time. This was recorded on audiotape and pictures were taken of what he wrote on the blackboard. From that, Leighton and Sands prepared the published texts.
The result reads and feels rather different from what one expects in a textbook. Having by now seen many video recordings of Feynman, when I read the lectures, I can almost hear the tapping of the chalk on the board as he writes out an equation and follows it up with some wisecrack in his exaggerated New York City accent. Sometimes you can see him thinking his way through an argument, as if in real time. This can be instructive and fascinating it its own way, but it doesn’t always accord with the authoritativeness that we expect from a bound and printed volume.
Moreover, if you don’t make a sustained effort to follow Feynman’s arguments in detail (ideally with pencil and paper at hand) you can be distracted by this informal style. Rest assured that Feynman is always serious, despite his jokes. Sometimes he glosses over some mathematical or logical steps in a derivation, but he almost always warns you about it. If you take the trouble to understand what a lecture says in detail, then you can be confident that you’ve learned the relevant physics. You should then work out the corresponding problems in the Exercises for The Feynman Lectures on Physics.
The other issue is that the lectures really cover too much material for the corresponding space, if they’re really intended to teach the student the subject from scratch. Indeed, there are lectures on topics (diffusion, stress and strain tensors, elastic solids, fluids, the magnetic properties of matter, crystallography, superconductors, etc.) that weren’t included any of the courses that I took during my four years of undergraduate plus five years of graduate education in physics. And the lectures incorporate several special topics (color vision, surface and shock waves, curved spaces, atmospheric electricity, etc.) that reflect Feynman’s own quirky interests.
There are some parts of the lectures that I’ve found confusing. There are some pedagogical choices that I find definitely outdated (e.g., using a velocity-dependent mass in special relativity, or covering the least-action formulation of classical mechanics only in a brief special lecture). Occasionally, Feynman says something that I think is a bit wrong (e.g., that the centrifugal force drives the circulation of a Taylor cell in Couette flow). But there are very few physics texts to which I’ve returned so often and with so much profit and enjoyment as to the Feynman Lectures.
I should add that I only glanced at them very superficially in high school and college. I finally bought my own copy after the professor for the advanced quantum mechanics course recommended owning them and reading through volume III if “you intend to continue thinking about physics at all in the future” (an odd comment, since the course was intended for first-year graduate students in physics at Harvard, even though I was taking it as a college senior). Many of the lectures I read for the first time when I was already a postdoc, and some I haven’t read at all.
Top Physics Books for MDCAT preparation
Physics by Nelkon and Parker
2. Physics by Halliday and Resnik
3. Lectures on Physics by Feynman
4. University physics by Zamansky
5. Nuclear physics by Kaplan
6. Quantum mechanics by Schiff
7. Classical mechanics by Goldstein
8. Optics by Ghatak
9. Electromagnetic by Sadiku
10. Motion Mountain by Christoph Schiller – 5 volumes
11. Physics by Tipler- 2 volumes
12. Problems in physics by Irodov
13. Electrodynamics by JD Jackson
14. Science of everyday things – volume on physics – notes
15. Physics demystified by McGraw Hill publications
I would divide the experience into three. What is it like to understand classical physics? What is it like to understand quantum physics? What is it like to understand very advanced physics?
On classical physics:
I see the world as a cartoon, as an idealized version of the real world, where you only focus on the essential features relevant to the physical phenomena you want to study.
If you want to know how long, it takes a cliff diver to hit the water. I would think about a dot moving downwards towards a line. And I would ask myself what physical forces apply here. Then I would think about the gravitational field as the background of the dot and line, with lots of arrows pointing down.
After this qualitative assessment, I would put formulas to this world, and then I would get a set of equations, which I need to solve. Then I assign numbers to different variables in the formula: like height, weight, gravitational strength, and compute the result.
Once I have an answer, I ask myself: does this answer make sense? did i make a mistake? And what error margin does the answer have? And I would feel the need to test it by jumping off the cliff.
If it’s not the right answer, I would re-check everything. And if it’s still not the same as the real thing, I will add details to the cartoon world. Maybe replace the dot by a box and the empty space by lots of little balls to represent air. And so on. I would never question that there is a cartoon world that is a good representation, but I would find myself not intelligent enough to find it. Sometimes you have the right world, but you are unable to solve the equations or find the numbers of the system.
Understanding a physical phenomenon feels like completely understanding a mechanical clockwork or another device. You know all the bits and pieces that are important.
Often, physicists are however staring at the clockwork and ask themselves: Now how the hell does this work? Which cartoon world do I need to construct to understand it?
On quantum physics:
I think of quantum physics as the rules on how the quantum world works. The quantum world is for me the world when you zoom to the level of atoms from the cartoon world.
Once at the quantum level, I think of the world as being smeared out and foggy. I feel that I know in which area an atom or electron is, but I don’t know exactly anymore where it is. And if I go and find it by measuring, I know the answer, but I have disturbed the system and it will evolve differently to when I did not measure it. I think of physical objects not as waves or particles, but as behaving like waves or particles.
But in general, I think of quantum physics as a set of rules or an algorithm on how to compute properties of the quantum world. And do not ask me what it means, except if i only think of what it means. But in 99% of the cases physicists just try to build a cartoon world of the quantum system and apply the rules of quantum physics. And much of the same applies to checking the answer, except that you need to make many different measurements to have an average answer.
As quantum physics is applied to fast-moving systems i.e., quantum field theory. The story becomes more complicated, and much of the thinking is done within mathematical frameworks. You start to think more in terms of a formula/mathematical concept world than a cartoon world.
On very advanced physics:
General relativity is like the classical world. Just a bit more complex as you need to deal with advanced mathematics like topology or differential geometry to describe physics in curved space-time. But it’s still the cartoon world. No major conceptual issues as in quantum mechanics… just the difficulty to do experiments and find the right cartoon world.
Finally, from time to time and depending on what you work on, you focus on the structure of the formulas themselves and not on a specific system you want to model. Here, you live entirely in a formula/mathematical world, and you try to see the connections between the different models. Is there a more general model that encompasses several models within?
It feels like you are climbing up higher and higher mountains. And more and more you see the whole landscape. From time to time, physicists make jumps in understanding, maybe from the highest mountain to seeing the whole earth from a satellite. But that also means we don’t care anymore about what happens in the valleys.
But 99% of the time in research, you feel stupid and clueless. You can’t see the wood for the trees. You follow all logical steps up to the place you get stuck many times over many days and from slightly different angles. You ask colleagues and consult books, which often leaves you more confused. And then suddenly ideas connect, and you re-read several times over several days. And then it becomes so obvious that you tell yourself: “why didn’t I get this earlier, it’s so obvious”. Then over the following weeks, someone asks a question about it, or you hit another obstacle, and you realize that you didn’t really understand it 100%. This process repeats itself a few times until you really understand it 100%. And then it becomes obvious and beautiful. To you. but not to the people you try to explain it to!
Most of the time, it’s just trying to understand what others have done, rather than finding something yourself. And you just add a tiny little bit or re-formulate something providing a slightly different angle on the topic.
Curiously, in very advanced physics, you suddenly live in many different possible worlds, because theorists are proposing different models on how the real world actually is and no-one knows what the appropriate model is. Ironically, you go from a fuzzy world filled with many totally different phenomena to a world described by relatively simple laws of physics to a world that is much less determined as no-one knows what its real structure at a fundamental level is.
