Each and every total eclipse of the Sun has a profound effect on its observers. People describe a feeling of connectedness to the Universe, a surreal sense of time standing still, a feeling of deep awe and respect for the powers of Nature, many to the point of becoming teary-eyed, euphoric, or even a little scared.
But the eclipse that occurred a century ago did more than that. It changed the very way that not only scientists, but also the public, viewed their Universe.
Albert Einstein’s general theory of relativity was confirmed directly by a total eclipse of the Sun that occurred 100 years ago this month, on May 29, 1919.
In 1919, people desperately needed a way to hit the reset button. The first World War had devastated many nations, and the influenza pandemic of 1918-19 had killed at least 50 million people worldwide. All those bullets and viruses had been operating under Newtonian mechanics, and it was time for a fundamental change.
Measurements of the positions of stars made during the eclipse of May 29, 1919 showed that this change was in fact at hand, and the resulting fervor propelled Albert Einstein to worldwide fame.
Shortly after the data from the eclipse had been assembled, analyzed, and presented at a meeting of the Royal Astronomical Society in London in November of that year, the New York Times announced that the world — indeed, the entire Universe — would no longer be the same, and they did so with a brilliant headline, one that must be among the best of all time:
Einstein had predicted something radical in 1915: A massive object like the Sun doesn’t merely pull on things, as Isaac Newton had said. Rather, it also warps space itself (not to mention slowing time down a bit), so that a beam of light dutifully traveling in a “straight” line should have a noticeably curved path if it gets too close. This figure exaggerates the effect a bit to get the point across:
Our brains don’t factor in the curvature of space when we look at things. We assume that light always moves in a straight line, the kind that Euclid (the “Father of Geometry”) meant. So a star whose light gets close to the Sun on its way to Earth would appear to us as though it’s a little farther away from the Sun than it actually is.
Other big objects near us deflect things too, but not quite like the Sun. Jupiter achieves about 1% of the Sun’s deflection, but that’s too small to measure. So if you want to see these deflections, you have to use the Sun, and because it’s so bright, there’s only one way to do that.
During a total eclipse.
It might surprise you to know that Newton’s equations, like Einstein’s, predict that light should be attracted by a massive body, even though light has no mass. Remember that a feather and a hammer are both accelerated by gravity at the same rate, as astronaut David Scott demonstrated on the Moon:
You can extend this all the way down to massless light. If a beam of light were to stop somehow, it would fall to Earth like anything else.
But Einstein’s new wrinkle led him to predict that the Sun should deflect light by twice the amount Newton would have predicted. These weren’t the only theories of the day, either; some top physicists like Finland’s Gunnar Nordström thought that light shouldn’t be deflected at all by an object like the Sun.
How large a deflection are we talking about? Would it be obvious? The largest, Einstein’s, for a star appearing right next to the Sun, was a projected 1.75 arcseconds. That’s about the same deflection as the breadth of a dime viewed from 1.3 miles away. That’s tiny! But it is measurable.
Einstein had already had some success with his theory of relativity, because it correctly predicted a quirk in Mercury’s orbit that other theories couldn’t account for. But people treated this more as a “post-diction” than a prediction at the time, because after all, Einstein already knew about it when he formulated his equations.
The eclipse, though, would be a showdown, and no one knew what the result would be.
The first World War had made scientific expeditions a bit challenging, to say the least. To do the measurements necessary to find the winning theory, you’d need to lug all your equipment to the site of a total eclipse, possibly on another continent, which at that time could take months.
But you also had to spend time making reference measurements of the normal positions of the stars for comparison. If the eclipse occurred in the middle of the day, you might have to be at the site months beforehand or afterward in order to catch the stars at night that would be out during the day when the eclipse came. That’s among the many, many reasons why a lot of people had failed:
The bending of light by gravity was the most stunning and obvious prediction of Einstein's theory. Astronomers had been trying to detect the effect at solar eclipses since before he had even finished formulating the theory. Nature and politics did not always cooperate.
One of the earliest to try was Erwin Finlay-Freundlich, an astronomer at the Berlin Observatory who was to become a big Einstein booster. Freundlich led an expedition to the Crimea in 1914 to observe an eclipse, but World War I began and he was arrested as a spy before the eclipse occurred. A team from the Lick Observatory in California did make it to the Crimean eclipse — but it rained. [...]
Worse, Lick's special eclipse camera was impounded by the Russians and not returned in time for the next eclipse, in Venezuela in 1916.
The next big chance to prove Einstein correct came in 1918, when the moon's shadow tracked right up the Columbia River between Washington State and Oregon. Lick sent another team of observers, but their camera was still not back from the Crimea and their improvised optics fell short, leaving the stars looking like fuzzy dumbbells as darkness fell.
The first team to finally successfully make these measurements after the war was this one:
Sir Arthur Eddington and E.T. Cottingham went to the island of Príncipe, while Andrew Crommelin and Charles Davidson went to the Brazilian town of Sobral. Sir Frank Watson Dyson arranged the expeditions and helped pore over the calculations.
It certainly helped that totality for this one would be more than 6 minutes long. Our 2017 American eclipse (which was spectacular nonetheless for those of us viewing it in Wyoming) only had a totality of 2 minutes and change.
Dyson was skeptical of Einstein’s claims, while Eddington was so sure they were correct that he considered the trip nothing more than an annoying formality. But they were both objective guys who knew it was important to demonstrate the correct answer. They knew we’d be talking about it 100 years later, and here we are! The results were awaited eagerly, even if one could only follow the progress by telegraph:
The star you see in this diary’s title photo is kappa Tauri-1, and that star appears as No. 4 in the diagram below, which points out the stars referred to in the Dyson-Eddington-Davidson paper on a real photo of the night sky. You’re looking at exactly what Eddington and Davidson would be watching for:
Their original drawing, for comparison with the photo:
These are the stars for which they would measure deflection, or displacement, from their normal positions. Some stars, like No. 1, got lost in the corona, but many were spotted and their positions measured, then compared to the ones on the reference plate (photograph). These stars were deflected more the closer they got to the Sun, and by plotting out their deflections, you could calculate the deflection for a hypothetical star right next to the Sun.
So, whose value would win? Einstein at 1.75 arcseconds, Newton at 0.87, or Nordström at 0.00?
The deflection at Sobral came out to 1.98 arcseconds, while the Príncipe number was 1.63 arcseconds. The Sobral data are shown below, with distance from the center of the Sun in arcminutes (‘) across the bottom of the graph, and displacement of a star’s position in arcseconds (“) up the left side of the graph. Each dot represents one star. The green line is the best fit to the actual data. The other lines are the predictions of the prevailing theories of the day:
Einstein had won. Relativity was real. Now the Universe was different.
Given his own careful consideration of all the data, even the skeptical (but objective) Dyson ultimately had to conclude in his own words:
The world had to stop and take a breath, because the ramifications were enormous. There was a whole lot more to Einstein’s laws than stars moving around a little bit during an eclipse.
Einstein had changed what is meant by “space” and “time”. He said that they are not fixed, universal things, as Newton had considered them. Newton said that two events could objectively be called simultaneous, because clocks everywhere run the same, at every point in space and for every observer. But Einstein said Newton was wrong, and that there is no such thing as simultaneous events; it all depends on your reference frame.
In other words, our intuition about what space and time are was completely wrong.
Space and time don’t define the speed of light. The speed of light defines space and time. Let’s say you build a race car that can go 184,400 miles per second (99% the speed of light), and you decide to have a race against a light beam. When the beam of light passes you, you won’t measure its speed at 1% the speed of light, because we don’t live in a Newtonian Universe. You’ll measure it zipping past you at 100% the speed of light, because we live in an Einsteinian Universe. When you’re moving, time slows down, and lengths become shorter. The speed of light is the same in all reference frames, even for you, in your ultrafast race car.
Einstein’s most famous equation, of course, is E = mc2. It means that if you’re sitting still (not moving through space), you possess energy (E) that equals your mass (m) times the speed of light (c) squared.
That’s a gargantuan amount of energy. It’s actually hard to express just how much energy it is. For an average human, it’s enough to light a 100-watt light bulb … for 2 billion years. It’s enough to lift Mount Everest … 2.4 miles into the air. It’s enough to bring Utah’s Great Salt Lake to the boiling point.
Where does all this energy come from? It’s kinetic energy, because even though you’re sitting still in space, you are moving through time … at the speed of light. Stopping that huge momentum would release a crapload of energy.
These things still strike us (or at least some of us, like me) as pretty profoundly messed up. So imagine how they struck the people of 100 years ago, who had never thought of anything this way.
We’ve had many, many experimental confirmations of Einstein’s theory of relativity since then.
We now know (among many other things) that:
During the 2017 eclipse, at least one guy, Donald G. Bruns, took it upon himself to repeat the solar deflection measurements as accurately as has ever been attempted. He got 1.752 arcseconds, plus or minus 3.4%. That’s really, really close to Einstein’s prediction:
This year the city of Sobral is getting ready to commemorate 100 years since the eclipse that changed the world.
The sculpture of the scientist Albert Einstein commissioned by City Hall is already in Sobral for commemorations of the 100 years of proof of the Theory of Relativity. The piece, molded in clay and cast in bronze, was created by award-winning Brazilian artist Murilo Sá Toledo, author of dozens of works set in squares and parks of several Brazilian cities. The sculpture of Einstein, which weighs 130 kilograms, seeks a faithful reproduction of the scientist.
Albert Einstein emigrated to the United States in 1933. He could see the writing on the wall in Germany:
While Albert Einstein was visiting the United States in 1933, the appointment of Adolf Hitler as chancellor took effect and the Jewish theoretical physicist decided he would not return to his home in Germany where he had been a professor at the Berlin Academy of Sciences. Einstein had been in the US for a visiting professorship at the California Institute of Technology in Pasadena at the time.
He and his wife Elsa returned by ship to Belgium in March 1933 to find that that their cottage had been raided. Einstein turned in his passport to the German consulate and formally renounced his German citizenship. By the summer, Einstein learned that his name was on a list of assassination targets.
He resided in Belgium for some months and then moved to England for a short period. On October 17, 1933, he returned to the US and took up a position at the Institute for Advanced Study at Princeton in New Jersey. The Princeton agreement required he stay for six months. With offers from numerous universities, including Oxford, Einstein was undecided on his future.
In 1935 Einstein decided to stay in the US and became a citizen in 1940. His affiliation with the Institute for Advanced Study would last until his death in 1955.
And who made out on that deal? The United States of America, the nation of immigrants. Where will the next Einstein come from? Mexico? Iran? Scotland? Ethiopia? Nepal? We don’t know. That’s why we can never close the door to immigrants. Bring ‘em in, and let ‘em show what they’ve got.
Einstein continued his contributions to science here in the U.S., of course, but he did some other things that not everyone is aware of:
Here’s something you probably don’t know about Albert Einstein.
In 1946, the Nobel Prize-winning physicist traveled to Lincoln University in Pennsylvania, the alma mater of Langston Hughes and Thurgood Marshall and the first school in America to grant college degrees to blacks. At Lincoln, Einstein gave a speech in which he called racism “a disease of white people,” and added, “I do not intend to be quiet about it.” He also received an honorary degree and gave a lecture on relativity to Lincoln students.
The reason Einstein’s visit to Lincoln is not better known is that it was virtually ignored by the mainstream press, which regularly covered Einstein’s speeches and activities. (Only the black press gave extensive coverage to the event.) Nor is there mention of the Lincoln visit in any of the major Einstein biographies or archives.
In fact, many significant details are missing from the numerous studies of Einstein’s life and work, most of them having to do with Einstein’s opposition to racism and his relationships with African Americans. [...]
“Einstein realized that African Americans in Princeton were treated like Jews in Germany,” said Taylor. “The town was strictly segregated. There was no high school that blacks could go to until the 1940s.” [...]
One woman remembered that Einstein paid the college tuition of a young man from the community. Another said that he invited Marian Anderson to stay at his home when the singer was refused a room at the Nassau Inn.
Some of the books out this year to observe the Eclipse’s centennial and Einstein’s revolution:
No Shadow of a Doubt: The 1919 Eclipse That Confirmed Einstein’s Theory of Relativity Daniel Kennefick Princeton University Press (2019)
Gravity’s Century: From Einstein’s Eclipse to Images of Black Holes Ron Cowen Harvard University Press (2019)
Einstein’s War: How Relativity Triumphed Amid the Vicious Nationalism of World War I Matthew Stanley Dutton (2019)
To conclude on a lighter note, we also remember the 1919 eclipse in sillier ways.
Behold the 1919 Solar Eclipse Bath Mat!
And a closing song to go with it:
I cannot tell you how much fun I had writing this diary.