How Richard Feynman’s Diagrams Revolutionized Physics

If you want to under­stand the­o­ret­i­cal physics these days—as much as is pos­si­ble with­out years of spe­cial­ized study—there are no short­age of places to turn on the inter­net. Of course, this was not the case in the ear­ly 1960s when Richard Feyn­man gave his famous series of lec­tures at Cal­tech. In pub­lished form, these lec­tures became the most pop­u­lar book on physics ever writ­ten. Feynman’s sub­se­quent auto­bi­o­graph­i­cal essays and acces­si­ble pub­lic appear­ances fur­ther solid­i­fied his rep­u­ta­tion as the fore­most pop­u­lar com­mu­ni­ca­tor of physics, “a fun-lov­ing, charis­mat­ic prac­ti­cal jok­er,” writes Mette Ilene Holm­nis at Quan­ta mag­a­zine, even if “his per­for­ma­tive sex­ism looks very dif­fer­ent to mod­ern eyes.”

Feynman’s genius went beyond that of “ordi­nary genius­es,” his men­tor, Hans Bethe, direc­tor of the Man­hat­tan Project, exclaimed: “Feyn­man was a magi­cian.” That may be so, but he was nev­er above reveal­ing how he learned his tricks, such that any­one could use his meth­ods, whether or not they could achieve his spec­tac­u­lar results. Feyn­man didn’t only teach his stu­dents, and his mil­lions of read­ers, about physics; he also taught them how to teach them­selves. The so-called “Feyn­man tech­nique” for effec­tive study­ing ensures that stu­dents don’t just par­rot knowl­edge, but that they can “iden­ti­fy any gaps” in their under­stand­ing, he empha­sized, and bol­ster weak points where they “can’t explain an idea sim­ply.”

Years before he became the fore­most pub­lic com­mu­ni­ca­tor of sci­ence, Feyn­man per­formed the same ser­vice for his col­leagues. “With physi­cists in the late 1940s strug­gling to refor­mu­late a rel­a­tivis­tic quan­tum the­o­ry describ­ing the inter­ac­tions of elec­tri­cal­ly charged par­ti­cles,” Holm­nis writes, “Feyn­man con­jured up some Nobel Prize-win­ning mag­ic. He intro­duced a visu­al method to sim­pli­fy the seem­ing­ly impos­si­ble cal­cu­la­tions need­ed to describe basic par­ti­cle inter­ac­tions.” The video above, ani­mat­ed by Holm­nis, shows just how sim­ple it was—just a few lines, squig­gles, cir­cles, and arrows.

Holm­nis quotes Feyn­man biog­ra­ph­er James Gle­ick’s descrip­tion: Feyn­man “took the half-made con­cep­tions of waves and par­ti­cles in the 1940s and shaped them into tools that ordi­nary physi­cists could use and under­stand.” Feyn­man Dia­grams helped make sense of quan­tum elec­tro­dy­nam­ics, a the­o­ry that “attempt­ed to cal­cu­late the prob­a­bil­i­ty of all pos­si­ble out­comes of par­ti­cle inter­ac­tions,” the video explains. Among the theory’s prob­lems was the writ­ing of “equa­tions meant keep­ing track of all inter­ac­tions, includ­ing vir­tu­al ones, a gru­el­ing, hope­less exer­cise for even the most orga­nized and patient physi­cist.”

Using his touch for the relat­able, Feyn­man drew his first dia­grams in 1948. They remain, wrote Nobel Prize-win­ning physi­cist Frank Wilczek, “a trea­sured asset in physics because they often pro­vide good approx­i­ma­tions to real­i­ty. They help us bring our pow­ers of visu­al imag­i­na­tion to bear on worlds we can’t actu­al­ly see.” Learn more about Feyn­man Dia­grams in the video above and at Holm­nis’ arti­cle in Quan­ta here.

Relat­ed Con­tent:

The “Feyn­man Tech­nique” for Study­ing Effec­tive­ly: An Ani­mat­ed Primer

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

What Made Richard Feyn­man One of the Most Admired Edu­ca­tors in the World

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

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