How a solar eclipse proved that Einstein was right

100 years ago this month, the theory of relativity was confirmed, and Einstein became famous overnight.

It's hard to imagine, but most people outside of the world of physics didn't know who Albert Einstein was in the early part of 1919. Even Einstein himself was facing his own self-doubt – he was going through a divorce and dealing with health issues. There was political turmoil in his home country of Germany. But by the end of the year, Einstein had become a celebrity practically overnight, known the world over. And it was because of a singular event that occurred on May 29, 1919, 100 years ago this month.

Einstein had published his theory of relativity a few years earlier, but it was still unproven. Conceptually, he knew that gravitational waves would cause warps in space-time, but there was a practical issue: he couldn’t properly measure it. But during a total solar eclipse, stars passing through the sun’s gravitational field would be visible, and accurate measurements could be made. Einstein just had to figure out a way to photograph an eclipse.

So he enlisted the help of British astronomer Sir Arthur Eddington. Eddington traveled to the island of Principe off the western coast of Africa to photograph the solar eclipse. Eddington also sent astronomers to Sobral, Brazil, in case it was cloudy where he was and he needed backup photos.

One of Eddington's photographs of the total solar eclipse of 1919. It confirmed Einstein's theory that light bends. One of Eddington's photographs of the total solar eclipse of 1919. It confirmed Einstein's theory that light bends. (Photo: Wikimedia)

They analyzed the data from the photographs and held a press conference in London to announce their findings. In that one moment, the theory of relativity overthrew Newton's law of gravity as the reigning theory in physics. The New York Times declared in an all-caps headline: "EINSTEIN THEORY TRIUMPHS." Einstein became instantly famous, recognized wherever he went. Two years later, he was awarded the Nobel Prize in Physics.

The minute book for the meeting where Eddington presented his findings, confirming Einstein's theory of general relativity. They include the line 'A general discussion followed. The President remarked that the 83rd meeting was historic.' The minute book for the science club where Eddington presented his findings, confirming Einstein's theory of general relativity. They include the line 'A general discussion followed. The President remarked that the 83rd meeting was historic.' (Photo: Wikimedia)

So seminal was story of the eclipse to Einstein's life that it was a major plot point throughout 2017's National Geographic miniseries "Genius" about the world's favorite genius.

"It's hard to think of a more important experiment in the 20th century," Daniel Kenneflick told From The Grapevine. He should know. Besides being a theoretical physicist at the University of Arkansas, Kenneflick is also the author of a new book about that historic event, perfectly timed to the centennial celebration. In "No Shadow of a Doubt: The 1919 Eclipse That Confirmed Einstein's Theory of Relativity," he details how expedition scientists overcame war, bad weather and equipment problems to test and prove one of science’s most fundamental theories.

Kenneflick got his Ph.D. at CalTech, a school where Einstein frequently lectured and home to the Einstein Papers Project. CalTech works hand-in-hand with the Hebrew University in Israel, where the official Albert Einstein Archives are kept, to make as complete a picture as possible of Einstein's legacy.

For research for his book, Kenneflick also traveled to Cambridge University, where Eddington's files are kept. "You have Eddington's letters home to his mother from while he was traveling on the eclipse expedition," he explained. "You have the minutes of the meeting where they had to plan everything under very difficult circumstances. You had the actual data analysis notes. It was very gripping and it really took a hold of me." The book also shines a light on some of the expeditions' lesser-known characters – including clockmaker Frank Dyson, and Erwin Findlay-Freundlich, whose attempts to photograph an eclipse in Crimea were foiled by clouds and his arrest.

Kenneflick, who previously wrote a book about Einstein's research on gravitational waves, felt a particular connection to both Einstein and Eddington. "Both men really faced difficulties for standing up for what they believed in. They were viewed as outsiders and maybe even oddballs." HBO even made a movie about Einstein and Eddington:

Now, 100 years later, Einstein's theory of relativity has been proved countless times over. Most recently, the first-ever photograph of a black hole verified that Einstein was correct with his equations.

Another total solar eclipse, almost exactly 100 years after the one that made Einstein famous, will occur on July 2, 2019. It will pass right over some of the biggest observatories in the world – including in South America, where one of Einstein's original expeditions was sent. But this time, Einstein fans might barely be watching.

"It's surprising how little scientific relevance it is," Kenneflick explained. Decades after 1919, scientists have discovered much easier ways to test Einstein's theory using quasars and radio telescopes. "They realized you didn't need an eclipse to do this experiment."

The news of Einstein's theory being proven by the eclipse made international headlines. The news of Einstein's theory being proven by the eclipse made international headlines. (Photo: Illustrated London News Group / Albert Einstein Archives)

MORE FROM THE GRAPEVINE:

Photos and SlideshowsPhotos and Slideshows

Related Topics: Albert Einstein, Science

How a solar eclipse proved that Einstein was right
100 years ago this month, the theory of relativity was confirmed, and Einstein became famous overnight.