We Just Proved Einstein's Theory of Relativity on a Galactic Scale for the First Time

Friday, 22 June 2018 - 12:15PM
Friday, 22 June 2018 - 12:15PM
We Just Proved Einstein's Theory of Relativity on a Galactic Scale for the First Time
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Image credit: NASA

When Einstein's theories overturned some of the fundamental ideas of Newtonian physics (and how scientists viewed the universe), it made him a celebrity almost overnight.


A century later, scientists are now trying to overturn relativity and take their place in history, but unfortunately for them it seems that relativity still holds up, even on a galactic scale:


A new study published in Science yesterday shows that the phenomenon of gravitational lensing, which is intimately connected to both gravity and relativity, allows scientists to get an accurate estimate of a galaxy's mass.

To carry out the study, astrophysicist Tom Collett, a research fellow at the University of Portsmouth in England, used two of the most sensitive and powerful telescopes around: The Hubble Telescope and the Very Large Telescope.


Both were pointed at a pair of galaxies that were aligned with Earth, with the nearest one floating in space about 450 million miles away.


Since one galaxy was positioned in front of the other, the light from the background galaxy was warped and magnified by the foreground galaxy's gravity, creating what's known as a "gravitational lens."


These have been used before by astronomers and astrophysicists to peer at distant objects, but Collett was measuring the amount of distortion and magnification to estimate the foreground galaxy's mass.


Since the amount of gravity a body exerts is tied directly to its mass, measuring the lensing effect should give an accurate estimate...unless Einstein's relativity breaks down at the galactic scale.


This was partly Collett's hope: to use the incredible power of Hubble and the VLT to find a crack in Einstein's model of relativity and show that gravity acts differently at different scales.


"Everyone would love to prove Einstein wrong. There is no better way to be famous," Tommaso Treu, an expert in gravitational lensing at the University of California, Los Angeles, told Scientific American.


"Overturning the consensus is usually very, very difficult at first-but usually pays off greatly."


Unfortunately, the two telescopes came to basically the same answer:


"We know the mass of the foreground galaxy from MUSE and we measured the amount of gravitational lensing we see from Hubble," said Collett.


"We then compared these two ways to measure the strength of gravity—and the result was just what general relativity predicts, with an uncertainty of only nine percent. This is the most precise test of general relativity outside the Milky Way to date." 

Though Collett won't go down in history as the man who proved brought down Einstein, he's not bitter about it.


According to him: "It is so satisfying to use the best telescopes in the world to challenge Einstein, only to find out how right he was."

Science News