The total solar eclipse and a 1915 Einstein theory
Among the millions of people positioning themselves to view yesterday’s total solar eclipse across North America, a group of researchers had a bigger mission in mind than simply experiencing totality, writes Kasha Patel, from a small town in Mexico.
Three hours before the total solar eclipse, the sky over El Salto in Mexico had only a few wispy clouds. “It looks good,” said Toby Dittrich, a physics professor at Portland Community College.
For him, the eclipse wasn’t about the pictures of an occulted sun – although that was enough for millions of other eclipse viewers to gather under its path from Mazatlán, Mexico, to Canada.
For the professor, it was about using the rare celestial phenomenon to understand our universe like never before.
Dittrich and a group of students travelled to Mexico 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 spacetime must be curved instead of flat as Isaac Newton had predicted. Since the experiment was performed with rudimentary instruments in 1919, however, scientists have run only a limited number of loose follow-on tests.
Dittrich wasn’t satisfied with that situation.
“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, Texas, Dittrich and a group of fellow physics professors, amateur astronomers and undergraduate students travelled more than 2000 miles (3200km) to the outskirts of El Salto, Durango, a small mountainous town in north-central Mexico.
This remote area lies at the centre of the eclipse shadow, providing four minutes and 30 seconds of totality - the maximum time that anyone would experience during Monday’s eclipse (Tuesday NZT).
The hope was that the location 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-yearold Einstein, yet to reach major stardom, published a radical new idea in 1915 on how gravity worked.
Previously, Newton had 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, Oregon, who also travelled to El Salto.
Einstein did the maths to prove his theory, but he also suggested that 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 is 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 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 the 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