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Why this eclipse could really prove Einstein was correct
By · Kasha Patel The Washington Post
Published April 08, 2024
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EL SALTO, Mexico Three hours before the total solar eclipse, the sky had only a few wispy clouds.
"It looks good," said Toby Dittrich, a physics professor at Portland Community College.
For him, the eclipse isn't about the pictures of an occulted sun - although that's enough for millions of other eclipse viewers gathering under its path from Mazatlán, Mexico, to Canada. Instead, he wants to use the celestial phenomenon to understand our universe like never before.
Dittrich and a group of students are planning to run one of the most famous astronomical experiments in history - one that proved Albert Einstein's theory of general relativity. It showed how our massive sun bends starlight around it, showing that space-time must be curved instead of flat as Isaac Newton had predicted. Since it was performed with rudimentary instruments in 1919, though, scientists have run only a limited number of loose follow-on tests.
Dittrich wasn't satisfied. "No one really believes that [Einstein's theory] isn't true because of theoretical calculations," he said. "But no one has actually satisfactorily proven it."
So instead of heading to sought-after eclipse-viewing destinations such as Mazatlán or Austin, Dittrich and a group of fellow physics professors, amateur astronomers and undergraduate students traveled more than 2,000 miles to the outskirts of El Salto, Durango, a small mountainous town in north-central Mexico.
This remote area is at the center of the eclipse shadow, providing 4 minutes and 30 seconds of totality - the maximum time that anyone will experience during this eclipse. It might also shed unprecedented data that would verify Einstein's mathematical model without a doubt.
• 105 years before this eclipse
The journey of Dittrich's 2024 experiment began more than a century ago. A 36-year-old Einstein, yet to reach major stardom, published a radical new idea in 1915 on how gravity worked.
Previously, Newton proposed that gravity occurred in a flat, uniform space. But in Einstein's universe, space and time (which are inextricably linked together) are curved, getting pushed, pulled, stretched and warped by matter.
"If you get really close to really massive things, things get weird," said Daniel Borrero Echeverry, a physics professor at Willamette University in Salem, Ore., who also traveled to El Salto.
Einstein did the math to prove his theory, but he suggested one way of measuring it in the real world would be by recording the position of the stars close to the sun when the sun is out and compare it to when it's absent. It's difficult to image stars in broad daylight because the sun washes them out, though - unless a total solar eclipse blocks the sun's surface, allowing scientists to see details along its outer edge.
Einstein's general relativity theory predicted that the massive sun should bend the light of surrounding stars by about twice as much as predicted per Newton's theory - a change too small to detect with a human eye but potentially visible with telescopes at that time.
Enter British astronomers Sir Arthur Eddington and Frank Dyson. In 1919, they hauled their instruments from Britain to northern Brazil and West Africa to measure starlight during a total solar eclipse. They captured a total of 14 stars that showed the light deflection that Einstein predicted, although the margin of error was large.
Nonetheless, they proclaimed Einstein was correct, launching the physicist into the mainstream celebrity status that we know today. "EINSTEIN THEORY TRIUMPHS," the New York Times wrote on its front page.
This eclipse, Dittrich, Borrero Echeverry and a handful of student and faculty researchers geared up to redo the 1919 Eddington experiment in unmatched detail with better ground telescopes and thousands of sky images. They specifically want to measure stars extremely close to the sun's edge - the "forbidden zone" where they often get washed out by the bright sunlight.
• 7 years to the eclipse
This is no easy experiment. Over the years, several research teams have tried to re-create it, but they either failed, produced too large margins of error or didn't capture enough data.
Dittrich and fellow physicist Richard Berry tried in August 2017, but it's not something Dittrich really brags about. While the data set was good, the calibration of his telescopes were off. His margin of error ended up to be 50 percent, more than the original Eddington experiment. He attempted the experiment again during a total solar eclipse in Chile in December 2020, but rain and clouds got in the way.
Satellite missions and radio telescopes have made extremely precise measurements of starlight deflection over the past few decades, but none of these expensive projects imaged stars in Dittrich's coveted forbidden zone.
The most promising Eddington experiment to date, by physicist and amateur astronomer Don Bruns, managed to capture 40 stars in the forbidden zone during the 2017 eclipse.
Equipped with 13 high-resolution telescopes with cameras deployed across Mexico and Texas, Dittrich's 2024 team of student and faculty researchers could collect millions of data points that would offer a much sharper picture of this elusive area than ever before: They expect to image 200,000 stars.
It's like you're painting a picture of a tree and all you have is a brown trunk, said Dittrich. More data from the forbidden zone would be like filling in details about that tree's bark.
• 7 days to the eclipse
Traveling in his 1973 Volvo station wagon, Dittrich hauled a 10-foot trailer carrying about 800 pounds of equipment: tools, chairs, tables, laptops, cameras and five telescopes worth $11,000 total in boxes he custom-made.
Crossing the border into Mexico, Dittrich became scared that a federal officer who pulled him over might confiscate all that equipment - after all, the same thing happened to Eddington in 1914 en route to Crimea to conduct his experiment during World War I.
The officer let him through, not without taking the pesos out of Dittrich's wallet and a handful of eclipse glasses.
• 5 days to the eclipse
Once at their destination, an upscale neighborhood complex about 20 minutes away from El Salto, the team unloaded their boxes.
It took them about five full days at the site to prepare for the approximately 4 minutes and 30 seconds of full totality, not counting the months to years of preparation beforehand.
They mounted the telescopes, connected battery packs and upgraded the software to control their instruments and analyze the data. They assembled solar filters made from round cardboard oatmeal containers and galaxy-designed duct tape (totaling less than $20) to place over the expensive telescopes so the instruments won't fry as they stare at the sun.
Then it was time to work out any kinks before the big show. Telescopes that were supposed to autonomously point to the North Star moved straight to ground: instrument error. Someone bumped a telescope, so it needed to be recalibrated: human error. If the eclipse is hidden by clouds, that would be an Earth error.
Sixteen hours before the eclipse, all five telescopes were detecting the starlight deflection to an accuracy of 0.05 arcseconds - a promising result that points to this being the most accurate Eddington experiment ever conducted.
Now, they just had to wait until 12:10 p.m. Central on Monday to see if it works for real.
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