May 9, 1921: Albert Einstein, the most famous scientist in the world, stood on stage in McCosh 50, Princeton University’s largest lecture hall.

He wore a black cloak, creased trousers, and a green knitted tie, and drew imaginary lines with chalk as he addressed his audience, according to the Evening Bulletin of Philadelphia: “The long hair that ended in tight curls and the chalk balanced between his fingers like a baton gave him the appearance of an orchestra conductor.”

Earlier in the day, Princeton had awarded Einstein — age 42 — an honorary degree. President John Grier Hibben 1882 compared him to Pythagoras, Galileo, and Newton. Graduate School Dean Andrew Fleming West 1874 described Einstein as a Columbus “voyaging through strange seas of thought alone.” Now he would explain to the general public his astonishing, famously abstruse theory of relativity. 

The room was packed. The 400 attendees included visiting scientists, curious members of the public, and reporters from major newspapers. They had come to see the man reputed to have overthrown Newton, rewritten the laws of physics, eradicated classical notions of time and space, accurately predicted the bizarre bending of starlight, and had done this with nothing more than the power of his mind.

“Ladies and gentlemen!” Einstein began. He immediately assured his audience that his lecture would have minimal mathematical elements. He then explained the concept of relative motion, something pondered by Galileo nearly 300 years earlier. 

“The theory of relativity is so named because this whole theory is concerned with the question of the extent to which any motion is merely relative motion,” Einstein said. “For example, when we speak of a car moving in the street, the motion refers to the piece of ground or surface called the road and this piece of Earth’s surfaces plays the role of a body on which this motion will develop. Thus, the very idea of motion is relative motion, and according to the conception of motion one could equally well say the street moves relative to the car, as we can say the car moves relative to the street.”

Except he said all this in German. (His actual opening words: “Meine Damen und Herren!”) 

This was the first of five Stafford Little Lectures he had agreed to give on successive days. The first two were “popular” lectures, followed by three of a more technical nature for scientists. A stenographer took notes in German in shorthand, and she handed these to a Princeton physics professor, Edwin Adams, who then summarized the lectures orally in English. (In 1921 an American physicist had no choice but to be fluent in German, since Germany was then the center of the physics world.) 

Einstein’s audiences shrank as the days progressed, likely as people realized that his theories remained incomprehensible even in translation. By lecture three he was speaking in a small classroom, according to The Formative Years of Relativity: The History and Meaning of Einstein’s Princeton Lectures, by Hanoch Gutfreund and Jürgen Renn. 

But the Gutfreund-Renn volume explains why the lectures were far more than a momentary status-enhancing chapter in Princeton history. The lectures, condensed from five to four, formed the basis for a book, The Meaning of Relativity, published by Princeton University Press in January 1923 and in print ever since, with Einstein adding appendices over the ensuing decades. Einstein had previously written a popular book on relativity, published in 1917. The Meaning of Relativity became one of the two canonical Einstein texts on relativity. According to Princeton historian Michael Gordin, the geometry used by Einstein to develop his theory was unfamiliar to many scientists at the time, and the new book helped them understand it. 

Gutfreund and Renn write: “Neither before nor afterward did he offer a similarly comprehensive exposition that included not only the theory’s technical apparatus but also detailed explanations making his achievement accessible to readers with a certain mathematical knowledge but no prior familiarity with relativity theory.”

Einstein’s theory of relativity was not a singular construct but rather an elaborate edifice constructed over more than a decade. In his “miracle year” of 1905, when he produced an explosion of revolutionary insights, he produced what would later be called the Special Theory of Relativity. He explained that there is no master clock in the universe, nor fixed points in space. No longer could anyone say two events happened at the same time. Simultaneous according to whom? 

Einstein’s universe was composed not of three dimensions but four — the fourth being time. He explained the concept of “time-space” in The Meaning of Relativity: “Upon giving up the hypothesis of the absolute character of time, particularly that of simultaneity, the four-dimensionality of the time-space concept was immediately recognized. It is neither the point in space, nor the instant in time, at which something happens that has physical reality, but only the event itself.”

Einstein said the reason experimentalists hadn’t been able to detect the effects of the ether assumed to permeate space was that it didn’t exist. The banishment of the ether hypothesis was a central feature of relativity, and it so happened that a report reached Einstein while he was at Princeton saying that an astronomer at Mount Wilson in California had, in fact, detected signs of the ether. That would have blown relativity theory to bits. Einstein was not perturbed: He knew he was right. He uttered a line that, when translated into English, became one of his most famous: “The Lord God is subtle, but malicious he is not.” 

In 1915 he managed to produce the equations that extended his theory to explain gravity, in what he called the General Theory of Relativity. Gravity, Einstein said, reflected the curvature of space and time in the presence of matter. No longer was gravity a spooky force acting at a distance; it was built into the fabric of the cosmos. 

Einstein and his wife Elsa in Washington, D.C., during their 1921 trip to the United States.
Photo 12/Universal Images Group via Getty Images

Relativity captivated scientists immediately, but Einstein did not become a global celebrity until 1919. That was when an observation of a solar eclipse confirmed a key prediction of his theory of relativity: that starlight would be diverted by the curvature of space near a massive object like the sun. The confirmation was announced by the British physicist Arthur Eddington, who had organized an expedition to an island off the coast of West Africa to observe the eclipse. The resulting media sensation was orchestrated by Eddington, and The New York Times published a breathless headline: “LIGHTS ALL ASKEW IN THE HEAVENS: Men of Science More or Less Agog Over Results of Eclipse Observations.”

The world would remain agog in the months and years to come. There was just one major problem with Einstein’s theory: Few people could understand it. 

Prior to Einstein’s Princeton appearance, The New York Daily News noted that 650 tickets to the lectures had been requested, and it ran the story under the cheeky headline “650 More People Would Understand Relativity.” 

In 1921 the world was still recovering from the trauma and industrial-scale slaughter of The Great War, as it was then known. The planet had also just emerged from a pandemic that left many millions dead. 

Daniel Okrent, a historian who has written extensively about the 1920s, tells PAW that the war “threw the world off its axis.” He points to a diary entry of Franklin Lane, the secretary of the interior, from January 1920: 

“The whole world is skew-jee, awry, distorted and altogether perverse. The President is broken in body, and obstinate in spirit. Clemenceau is beaten for an office he did not want. Einstein has declared the law of gravitation outgrown and decadent. Drink, consoling friend of a Perturbed World, is shut off; and all goes merry as a dance in hell!”

Einstein was a fascinating figure as he walked off the ship in New York carrying a pipe and a violin case. He was youthful still — not yet the rumpled, grandfatherly figure we know from T-shirts, posters, and coffee mugs. 

“Unlike the picture of the old man at Princeton with his chaotic mane of hair and his careless Chaplinesque attire, Einstein in midlife was an attractive, impressive man, whose features, eyes, speech, and mere presence aroused and indeed compelled attention,” writes the biographer Albrecht Fölsing. 

“He was a rock star whose fame exceeded that of Hawking,” says University of Chicago physicist Michael Turner. 

“It helps that Einstein is photogenic and gives good quotations,” Princeton historian Gordin says. “He is a media creation. There are photos of him with Charlie Chaplin, and it’s not a bad analogy — he’s a figure that fits that moment.”

The moment in 1921 was thoroughly modern. Einstein’s physics, as Walter Isaacson noted in his biography, resonated with the modernist movement in art, music and literature: “[M]odernism was born by the breaking of the old strictures and verities. A spontaneous combustion occurred that included the works of Einstein, Picasso, Matisse, Stravinsky, Schoenberg, Joyce, Eliot, Proust, Diaghilev, Freud, Wittgenstein, and dozens of other pathbreakers who seemed to break the bonds of classical thinking.”

And so people didn’t really mind that someone had come up with a theory they couldn’t understand. 

“I think what’s going on there is Einstein becomes more impressive as a sage insofar as he can’t be understood,” says New York University historian Matthew Stanley. “He’s talking about things so cosmic they’re beyond understanding. The fact that he understands them makes him more extraordinary. Einstein grasps this early on and plays to that.”

Cosmologist Katie Mack *09 of North Carolina State says that people like the idea that “there are these godlike supergeniuses that walk among us. ... There’s something about the archetype of the kind of crazy genius, somebody who has that kind of otherworldliness about them. Somebody who is not paying attention to fashion, he has weird hair, he has weird hobbies, he comes up with something nobody can understand.” 

The newspaper reporters struggled, with limited success, to translate Professor Adams’ translation of Einstein’s lectures into something readers could digest.

“By specific illustrations with equations he proved that his theory of the end to infinity was correct, as far as can be shown by algebra,” the New York Tribune reported. “The main basis of his belief is that density of matter is not equal to zero and, therefore, that all space is finite, thus disagreeing with Newton, who tried to prove that density of space equals zero and that space is, on that account, infinite.” 

The New York Times got closer to the gist of things: “We can no longer think of space, time and matter as independent concepts, but they are interwoven with each other.”

The final lecture incited this headline in the Times: “EINSTEIN CANNOT MEASURE UNIVERSE.” A smaller headline took a stab at an explanation: “Universe Called Finite and Yet Infinite Because of its Curved Nature.”

Einstein did not come to America to speak about relativity. Accompanied by his wife, Elsa, he came to raise money for the Hebrew University of Jerusalem. He was invited by, and traveled with, chemist Chaim Weizmann, then head of the Zionist movement in the United Kingdom and later the first president of Israel. 

Einstein was passionate in his support of the creation of the Hebrew University and would be present two years later at its inauguration. Amid the anti-Semitism in Germany (some critics of relativity derided it as “Jewish physics”), Einstein, though not religious, was identifying more closely with his Jewish brethren. He viewed his role on the trip as functional but somewhat undignified. He was a showpiece, paraded around in an effort to raise money from wealthy American Jews. He was quite blunt about it: 

“I had to let myself be paraded like a prize bull, and make a thousand speeches at big and small meetings,” he wrote to his friend Michele Besso.

Among those accompanying Einstein on his trip to the United States was Chaim Weizmann, second from right, a chemist who later became the first president of Israel.
FPG/Archive Photos/Getty Images

Einstein’s Princeton visit gave him a taste of life in a tranquil academic village. He would return a dozen years later. Amid the rise of the Nazis and intensifying militarism and anti-Semitism in Germany, Einstein renounced his German citizenship, and in 1933 was lured by Abraham Flexner to join the newly formed Institute for Advanced Study in Princeton. The institute had no building at first, so Einstein and a handful of other institute professors camped out at the University’s mathematics department in Fine Hall. 

“Princeton is a wonderful piece of earth and at the same time an exceedingly amusing ceremonial backwater of tiny spindle-shanked semigods,” he wrote soon after arriving in Princeton, according to Fölsing’s biography. 

The Einsteins bought a house at 112 Mercer St., a short walk from campus. Elsa Einstein became ill and died not long after. Her husband became something of a loner, seen in the community as an endearing eccentric, and known for his long rambles about town. Peripatetic for so much of his life, he stayed rooted in Princeton until his death in 1955.

What few people in the audience in McCosh 50 on May 9, 1921, could have known was that the bulk of Einstein’s most important scientific work was already behind him. Einstein remained ambitious in the years that followed, and his status as the preeminent scientific celebrity only solidified. But a new generation of brilliant thinkers pushed physics into stunning realms where Einstein was never fully comfortable. 

Einstein’s 1905 paper on the photoelectric effect (the only paper cited by the Royal Academy in awarding Einstein the Nobel Prize in 1922) was a foundational text of quantum physics, but Einstein was never happy with the probabilistic, indeterminate, causality-defying nature of the new physics, and famously declared that God does not throw dice. He spent much of his last three decades trying in vain to develop a “theory of everything” that would link all the fundamental forces in nature. 

The mythology of Einstein the genius can obscure the collaborative nature of scientific breakthroughs. In his 1905 miracle year, was he really a lone genius operating in the lowly job of patent clerk in Bern? Katie Mack says that’s wrong: Patent clerk was an important job, and Einstein was in contact with other physicists, building on their work.

Einstein at the door of his home on Mercer Street in Princeton, around 1951.
Keystone-France/Gamma-Keystone via Getty Images

Is it true that he overthrew Newton? Einstein himself denied that, as quoted by Fölsing: “There has been a false opinion widely spread among the general public that the theory of relativity is to be taken as differing radically from the previous developments in physics from the time of Galileo and Newton. The contrary is true.” At another point, according to Isaacson’s biography, Einstein derided cults of personality: “It strikes me as unfair, and even in bad taste, to select a few for boundless admiration, attributing superhuman powers of mind and character to them. This has been my fate, and the contrast between the popular estimate of my achievements and the reality is simply grotesque.” 

Einstein didn’t come up with “relativity” out of the blue. The term predated his theory. He didn’t think up the notion that objects contract as they accelerate: Hendrik Lorentz did. The field equations of general relativity were independently developed at the same time by David Hilbert. Even the “Eureka!” moment of the relativity story, the Eddington expedition’s confirmation of general relativity during the 1919 eclipse, has been questioned by scholars, who argue Eddington hyped ambiguous results. 

Einstein cuts an appealing figure as a humanist and pacificist, but biographers describe him as rakish, sexist, and cold to many of his closest relations, including his wives and children. Fame did not protect him from criticism, and as he weighed in on social and political issues, he often incited controversy and tension among his friends and fellow scientists. In 1921 he was still getting his footing as a celebrity scientist, and after he returned to Europe, he wrote an article criticizing Americans for being money-obsessed, among other failings. That did not go well back in the United States. He also gave an instantly notorious interview with a newspaper reporter in which he described American men as “toy dogs” of their women, whom he derided as superficial spendthrifts. That drew a rebuke in The New York Times, which suggested that Einstein stick to physics.

Such incidents are now footnotes in the Einstein biography. The controversies have largely receded from popular knowledge. Einstein became something more like the common property of humankind, an archetype of genius. 

But there is another Einstein characteristic that perhaps is too easily ignored: his fearlessness. It takes courage to push into uncharted realms and report unflinchingly on one’s discoveries, not all of which may be welcome. It’s not as if people were hankering to kick Newton to the curb. Even something as seemingly simple as a lecture tour in America took a great deal of verve and confidence — a willingness to plunge into new and potentially dangerous waters. Reading the accounts of Einstein trying to describe relativity to Americans, the reader feels compelled to give the man credit simply for showing up. 

There’s an odd passage at the close of one of the articles on Einstein’s Princeton lectures, which ran on May 12 in the Monmouth Democrat of Freehold, N.J.: “A fascinating inference of the theory of relativity is that ‘the apple,’ which Sir Isaac Newton observed falling in 1667, ‘is still falling.’” 

The story does not explain this observation or what Einstein said to prompt it. But Einstein’s theories do contain bizarre implications, including the equivalency of the past and future and the disappearance of a preferential point in time that we call “now.” 

And so, in a sense, Einstein is still there in McCosh 50, still waving his chalk like an orchestra conductor ­— still telling us the secrets of the universe.  

Joel Achenbach ’82 is a staff writer for The Washington Post.