Richard Feynman’s “Lost Lecture:” An Animated Retelling

Nobel prize-win­ning physi­cist Richard Feyn­man is “famous in a num­ber of dimen­sions,” says sci­ence and math explain­er Grant Sander­son of the YouTube chan­nel 3blue1brown in the video above. “To sci­en­tists, he’s a giant of 20th cen­tu­ry physics… to the pub­lic, he’s a refresh­ing con­tra­dic­tion to the stereo­types about physi­cists: a safe-crack­ing, bon­go-play­ing, mild­ly phi­lan­der­ing non-con­formist.” Feyn­man is also famous, or infa­mous, for his role in the Man­hat­tan Project and the build­ing of the first atom­ic bomb, after which the FBI kept tabs on him to make sure he would­n’t, like his col­league Klaus Fuchs, turn over nuclear secrets to the Sovi­ets.

He may have led an excep­tion­al­ly event­ful life for an aca­d­e­m­ic sci­en­tist, but to his stu­dents, he was first and fore­most “an excep­tion­al­ly skill­ful teacher… for his uncan­ny abil­i­ty to make com­pli­cat­ed top­ics feel nat­ur­al and approach­able.” Feynman’s teach­ing has since influ­enced mil­lions of read­ers of his wild­ly pop­u­lar mem­oirs and his lec­ture series, record­ed at Cal­tech and pub­lished in three vol­umes in the ear­ly 1960s. (Also see his famous course taught at Cor­nell.) For decades, Feyn­man fans could list off­hand sev­er­al exam­ples of the physicist’s acu­men for explain­ing com­plex ideas in sim­ple, but not sim­plis­tic, terms.

But it wasn’t until the mid-nineties that the pub­lic had access to one of the finest of his Cal­tech lec­tures. Dis­cov­ered in the 1990s and first pub­lished in 1996, the “lost lecture”—titled “The Motion of the Plan­ets Around the Sun”—“uses noth­ing more than advanced high school geom­e­try to explain why the plan­ets orbit the sun ellip­ti­cal­ly rather than in per­fect cir­cles,” as the Ama­zon descrip­tion sum­ma­rizes. You can pur­chase a copy for your­self, or hear it Feyn­man deliv­er for free just below.

Feyn­man gave the talk as the guest speak­er in a 1964 fresh­man physics class. He address­es them, he says, “just for the fun of it”; none of the mate­r­i­al would be on the test. Nev­er­the­less, he end­ed up host­ing an infor­mal 20-minute Q&A after­wards. Giv­en his audi­ence, Feyn­man assumes only the most basic pri­or knowl­edge of the sub­ject: an expla­na­tion for why the plan­ets make ellip­ti­cal orbit around the sun. “It ulti­mate­ly has to do with the inverse square law,” says Sander­son, “but why?”

Part of the prob­lem with the lec­ture, as its dis­cov­er­ers David and Judith Goodstein—husband and wife physi­cist and archivist at Caltech—found, involves Feynman’s exten­sive ref­er­ence to fig­ures he draws on the black­board. It took some time for the two to dig these dia­grams up in a set of class notes. In Sanderson’s video at the top, we get some­thing per­haps even bet­ter: ani­mat­ed phys­i­cal rep­re­sen­ta­tions of the math­e­mat­ics that deter­mine plan­e­tary motion. We need not know this math in depth to grasp what Feyn­man calls his “ele­men­tary” expla­na­tion.

“Ele­men­tary” in this case, despite com­mon usage, does not mean “easy,” Feyn­man says. It means “that very lit­tle is required to know ahead of time in order to under­stand it, except to have an infi­nite amount of intel­li­gence.” That last part is a typ­i­cal bit of humor. Even those of who haven’t pur­sued math or physics much beyond the high school lev­el can learn the basic out­lines of plan­e­tary motion in Feynman’s wit­ty lec­ture, sup­ple­ment­ed by the video visu­al aids Sander­son offers at the top.

Relat­ed Con­tent:

The Feyn­man Lec­tures on Physics, The Most Pop­u­lar Physics Book Ever Writ­ten, Is Now Com­plete­ly Online

‘The Char­ac­ter of Phys­i­cal Law’: Richard Feynman’s Leg­endary Course Pre­sent­ed at Cor­nell, 1964

Learn How Richard Feyn­man Cracked the Safes with Atom­ic Secrets at Los Alam­os

Richard Feyn­man on the Bon­gos

Richard Feyn­man Plays the Bon­gos

Josh Jones is a writer and musi­cian based in Durham, NC. Fol­low him at @jdmagness

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