Finishing Feynman Early

Have you ever finished what you thought of as a monumental (intellectual or otherwise) task early — such as finally writing up that paper, senior thesis, grant proposal etc. etc.  Well I just did.

It was finishing volume II of the Feynman Lectures on Physics on electromagnetism earlier than I had thought possible.  Feynman’s clarity of writing is legendary, which doesn’t mean that what he is writing about is simple or easy to grasp.  Going through vol. II is pleasant but intense intellectual work.

The volumes are paginated rather differently than most books.  Leighton and Sands wrote up each lecture as it was given, so each lecture is paginated, but the book isn’t paged sequentially.  Always wanting to know how much farther I had to, I added them together producing a running total as I read the book.  FYI  the 42 lectures (chapters) contain 531 pages.

So I’m plowing along through chapter 37 “Magnetic Materials” starting on p. 455 with its 13 pages knowing that there are still 63 intense pages to go at the end when I get to the last paragraph which begins “We now close our study of electricity and magnetism.”

Say what?  The rest is on fluid dynamics and elasticity (which I’m not terribly interested in).  So I’m done.  I feel like WilE Coyote chasing the roadrunner and suddenly running off a cliff.

However, the last chapter (42) is not to be missed for any of you.  It is the clearest explanation of curvature and curved space you’ll ever find.  All you need for the first 7 pages (which explains curvature) is high school geometry and the formula for the area of a circle (2 pi *r) and the volume of a sphere (4/3) * pi * r ^3.   That’s it.  Suitable for your nontechie friends.

Of course later on he uses the curvature of the space we live in to explain what Einstein did in general relativity and his principle of equivalence and his theory of gravitation (in another 7 pages).  I wish I’d read it before I tried to learn general relativity.

I did make an attempt to explain the Riemann curvature tensor — but it’s nowhere as good.

Here a link — https://luysii.wordpress.com/2020/02/03/the-reimann-curvature-tensor/

Here are links to my other posts on the Feynman Lectures on Physics

The pleasures of reading Feynman on Physics

The pleasures of reading Feynman on Physics – II

The pleasures of reading Feynman on Physics — III

The Pleasures of Reading Feynman on Physics – IV

The pleasures of reading Feynman on Physics – V

The pleasures of reading Feynman on Physics

“Traditionally, all courses in quantum mechanics have begun in the same way, retracing the path followed in the historical development of the subject.  One first learns a great deal about classical mechanics so that he will be able to understand how to solve the Schrodinger equation.  Then he spends a long time working out various solutions.  Only after a detailed study of this equation does he get to the advanced subject of the electron’s spin.”

From vol. III of the Feynman lectures on physics  p. 3 – 1.

Certainly that’s the way I was taught QM as a budding chemist in 1961. Nothing wrong with that.  For a chemist it is very useful to see how all those orbitals pop out of series solutions to the Schrodinger equation for the hydrogen atom.

“We have come to the conclusion that what are usually called the advanced parts of quantum mechanics are in fact, quite simple. The mathematics that is involved is particularly simple, involving simple algebraic operations and no differential equations or at most only very simple ones.”

Quite true, but when, 50 years or so later,  I audited a QM course at an elite woman’s college, the underlying linear algebra wasn’t taught — so I wrote a series of posts giving the basics of the linear algebra used in QM — start at https://luysii.wordpress.com/2010/01/04/linear-algebra-survival-guide-for-quantum-mechanics-i/ and follow the links (there are 8 more posts).

Even more interesting was the way Mathematica had changed the way quantum mechanics was taught — see https://luysii.wordpress.com/2009/09/22/what-hath-mathematica-wrought/

But back to Feynman:  I’m far from sure a neophyte could actually learn QM this way, but having mucked about using and being exposed to QM and its extensions for 60 years, Feynman’s development of the subject is simply a joy to read. Feynman starts out as a good physicist should with the experiments.  Nothing fancy, bullets are shot at a screen through a slit, then electrons then two slits, and the various conundrums arising when one slit is closed.

Onward and upward through the Stern Gerlach experiments and how matrices are involved (although Feynman doesn’t call them that).  The only flaw in what I’ve found so far is his treatment of phase factors (p. 4 -1 ).  They aren’t really defined, but they are crucial as phase factors are what breaks the objects of physics into fermions and bosons.

If you’ve taken any course in QM and have some time (who doesn’t now that we’re all essentially inmates in our own homes/apartments) than have a look.   You’ll love it.  As Bill Gates said about the books “It is good to sit at the feet of the master”.

One piece of advice — get the new Millennium edition — it has removed some 1,100 errors and misprints found over the decades, so if you’re studying it by yourself, you won’t be tripped up by a misprint in the text when you don’t understand something.