We lived in one world before August 6, 1945, and have lived in anoth­er ever since. Nobody under­stood this more clear­ly than Albert Ein­stein, who had advo­cat­ed for the research that cul­mi­nat­ed in that day. “A let­ter from Dr. Ein­stein in 1939 informed Pres­i­dent Roo­sevelt that the Ger­mans were engaged in the devel­op­ment of an atom­ic bomb and urged that sci­ence and tech­nol­o­gy in the Unit­ed States be mobi­lized on a sim­i­lar effort,” says a 1946 New York Times arti­cle. “This [1939] let­ter gave the first impe­tus to the devel­op­ment of the Atom­ic Bomb.” This sto­ry was includ­ed by way of con­text of a new call to action by Ein­stein and oth­er promi­nent sci­en­tists, one meant to secure human­i­ty’s future in a world with the bomb.

“Our world faces a cri­sis as yet unper­ceived by those pos­sess­ing pow­er to make great deci­sions for good or evil,” declares a telegram sent by Ein­stein to what the Times calls “sev­er­al hun­dred promi­nent Amer­i­cans.” “The unleashed pow­er of the atom has changed every­thing save our modes of think­ing and we thus drift toward unpar­al­leled cat­a­stro­phe. We sci­en­tists who released this immense pow­er have an over­whelm­ing respon­si­bil­i­ty in this world life-and-death strug­gle to har­ness the atom for the ben­e­fit of mankind and not for humanity’s destruc­tion.”

Hence the for­ma­tion of the Emer­gency Com­mit­tee of Atom­ic Sci­en­tists, chaired by Ein­stein and includ­ing as mem­bers such fig­ures as Hans A. Bethe, who’d direct­ed the The­o­ret­i­cal Divi­sion at Los Alam­os, and Leo Szi­lard, Ein­stein’s col­lab­o­ra­tor on the 1939 let­ter to Roo­sevelt.

Szi­lard also appears along Ein­stein in the col­orized short film clip above, in which they lis­ten to a ver­sion of their telegram read aloud “We beg you to sup­port our efforts to bring real­iza­tion to Amer­i­ca that mankind’s des­tiny is being decid­ed today, now, this moment,” reads the announc­er. The telegram itself spec­i­fies that “we need two hun­dred thou­sand dol­lars at once for a nation-wide cam­paign to let the peo­ple know that a new type of think­ing is essen­tial if mankind is to sur­vive and move toward high­er lev­els.” In oth­er words, one mind­set had enabled the cre­ation of nuclear weapons, and quite anoth­er was need­ed to pre­vent them from ever being used again. In 1954, the year before his death, Ein­stein wrote that “I made one great mis­take in my life — when I signed the let­ter to Pres­i­dent Roo­sevelt rec­om­mend­ing that atom bombs be made.” It’s one kind of ambi­tion to change the mind of a politi­cian, and quite anoth­er to change the mind of human­i­ty.

Relat­ed con­tent:

Albert Ein­stein in Four Col­or Films

Hear Albert Ein­stein Read “The Com­mon Lan­guage of Sci­ence” (1941)

Albert Ein­stein Explains Why We Need to Read the Clas­sics

Hear the Voice of Albert Ein­stein: Vin­tage Album Fea­tures Him Talk­ing About E=MC2, World Peace & More

“The Most Intel­li­gent Pho­to Ever Tak­en”: The 1927 Solvay Coun­cil Con­fer­ence, Fea­tur­ing Ein­stein, Bohr, Curie, Heisen­berg, Schrödinger & More

Based in Seoul, Col­in Marshall writes and broad­casts on cities, lan­guage, and cul­ture. His projects include the Sub­stack newslet­ter Books on Cities, the book The State­less City: a Walk through 21st-Cen­tu­ry Los Ange­les and the video series The City in Cin­e­ma. Fol­low him on Twit­ter at @colinmarshall or on Face­book.

The denial of sci­ence suf­fus­es Amer­i­can soci­ety, and no mat­ter what the data says, some con­ser­v­a­tive forces refuse efforts to cur­tail, or even study, cli­mate change. Astro­physi­cist Katie Mack calls this retrench­ment a form of “data nihilism,” writ­ing in an exas­per­at­ed tweet, “What is sci­ence? How can a thing be known? Is any­thing even real???” Indeed, what can we expect next from what Isaac Asi­mov called the Unit­ed States’ anti-intel­lec­tu­al “cult of igno­rance”? A flat earth lob­by?

Welp… at least a cou­ple celebri­ty fig­ures have come out as flat-earth­ers, per­haps the van­guard of an anti-round earth move­ment. Notably, [Dal­las Mav­er­icks] guard Kyrie Irv­ing made the claim on a pod­cast, insist­ing, Chris Matyszczyk writes, that “we were being lied to about such basic things by the glob­al elites.” Is this a joke? I hope so. Neil DeGrasse Tyson—who host­ed the recent Cos­mos remake to try and dis­pel such sci­en­tif­ic ignorance—replied all the same, not­ing that Irv­ing should “stay away from jobs that require… under­stand­ing of the nat­ur­al world.” The weird affair has played out like a sideshow next to the main­stage polit­i­cal cir­cus, an unset­tling reminder of Carl Sagan’s pre­dic­tion in his last book, The Demon Haunt­ed World, that Amer­i­cans would soon find their “crit­i­cal fac­ul­ties in decline, unable to dis­tin­guish between what feels good and what’s true.”

Sagan devot­ed much of his life to coun­ter­ing anti-sci­ence trends with warmth and enthu­si­asm, park­ing him­self “repeat­ed­ly, arguably com­pul­sive­ly, in front of TV cam­eras,” writes Joel Achen­bach at Smith­son­ian. We most remem­ber him for his orig­i­nal 1980 Cos­mos minis­eries, his most pub­lic role as a “gate­keep­er of sci­en­tif­ic cred­i­bil­i­ty,” as Achen­bach calls him. I think Sagan may have chafed at the descrip­tion. He want­ed to open the gates and let the pub­lic into sci­en­tif­ic inquiry. He char­i­ta­bly lis­tened to unsci­en­tif­ic the­o­ries, and patient­ly took the time to explain their flaws.

In the very first episode of Cos­mos, Sagan addressed the flat-earth­ers, indi­rect­ly, by explain­ing how Eratos­thenes (276–194 BC), a Libyan-Greek schol­ar and chief librar­i­an at the Library of Alexan­dria, dis­cov­ered over 2000 years ago that the earth is a sphere. Giv­en the geo­g­ra­ph­er, math­e­mati­cian, poet, his­to­ri­an, and astronomer’s incred­i­ble list of accomplishments—a sys­tem of lat­i­tude and lon­gi­tude, a map of the world, a sys­tem for find­ing prime numbers—this may not even rank as his high­est achieve­ment.

In the Cos­mos clip above, Sagan explains Eratos­thenes’ sci­en­tif­ic method: he made obser­va­tions of how shad­ows change length giv­en the posi­tion of the sun in the sky. Esti­mat­ing the dis­tance between the cities of Syene and Alexan­dria, he was then able to math­e­mat­i­cal­ly cal­cu­late the cir­cum­fer­ence of the earth, as Cyn­thia Stokes Brown explains at Khan Acad­e­my. Although “sev­er­al sources of error crept into Eratos­thenes’ cal­cu­la­tions and our inter­pre­ta­tion of them,” he nonethe­less suc­ceed­ed almost per­fect­ly. His esti­ma­tion: 250,000 sta­dia, or 25,000 miles. The actu­al cir­cum­fer­ence: 24,860 miles (40.008 kilo­me­ters).

No, of course the Earth isn’t flat. But Sagan’s les­son on how one sci­en­tist from antiq­ui­ty came to know that isn’t an exer­cise in debunk­ing. It’s a jour­ney into the move­ment of the solar sys­tem, into ancient sci­en­tif­ic his­to­ry, and most impor­tant­ly, per­haps, into the sci­en­tif­ic method, which does not rely on hearsay from “glob­al elites” or shad­owy fig­ures, but on the tools of obser­va­tion, infer­ence, rea­son­ing, and math. Pro­fes­sion­al sci­en­tists are not with­out their bias­es and con­flicts of inter­est, but the most fun­da­men­tal intel­lec­tu­al tools they use are avail­able to every­one on Earth.

Note: An ear­li­er ver­sion of this post appeared on our site in 2017. This ver­sion has been light­ly edit­ed and updat­ed.

Relat­ed Con­tent:

Carl Sagan Pre­dicts the Decline of Amer­i­ca: Unable to Know “What’s True,” We Will Slide, “With­out Notic­ing, Back into Super­sti­tion & Dark­ness” (1995)

Hear Carl Sagan Art­ful­ly Refute a Cre­ation­ist on a Talk Radio Show: “The Dar­win­ian Con­cept of Evo­lu­tion is Pro­found­ly Ver­i­fied”

Carl Sagan Presents His “Baloney Detec­tion Kit”: 8 Tools for Skep­ti­cal Think­ing

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