The theory of general relativity has just passed its first and most precise test outside the Milky Way.

We owe a lot of our current understanding of the Universe to Einstein’s equations and ideas.

The iconic physicist may have missed the mark on a few occasions, including his biggest blunder that the Universe is constant, but he got so many things right.

Read More: Einstein’s 3 Biggest Mistakes

Einstein’s legacy to the world can be summed in two words: General Relativity.

Now, scientists have, for the first time, proved the validity of Einstein’s theory in a distant galaxy, confirming their understanding of how gravity works.

General Relativity Succeeds its First Test on a Galactic Scale

Published in 1916, general relativity gets us back to the Universe’s early beginnings (the Big Bang), predicted the existence of gravitational waves, black holes, dark matter, and several other concepts that make up our current understanding of the cosmos.

Einstein’s work on gravity and his general relativity theory as a whole have stood the test of time, despite the attempts of scientists to find alternative theories that would describe the universe better.

Over the years, experimental tests time and time again proved general relativity, as a theory of gravity, to work — albeit only when confined to the walls of our solar system.

Researchers were wondering whether the same principles can apply to larger scales of the Universe, like a whole galaxy, and now they have the answer: it does!

Astrophysicists at the Institute of Cosmology and Gravitation (ICG) at the University of Portsmouth, UK, sought out to test general relativity on a galactic scale.

The team used data from two instruments, NASA’s Hubble Space Telescope and ESO Very Large Telescope in Chile, to study the light coming from a distant galaxy.

Researchers used a galaxy called ESO325-G004, 500 million light-years away, as a gravitational lense that bends the light from this distant galaxy generating what’s called an Einstein ring.

Dr Thomas Collett, leader of the study, explained:

“general relativity predicts that massive objects deform space-time, this means that when light passes near another galaxy the light’s path is deflected. If two galaxies are aligned along our line of sight this can give rise to a phenomenon, called strong gravitational lensing, where we see multiple images of the background galaxy. If we know the mass of the foreground galaxy, then the amount of separation between the multiple images tells us if general relativity is the correct theory of gravity on galactic scales.”

Then, after comparing the mass of ESO 325-G004 to the curvature of the surrounding spacetime, results showed that gravity behaves as predicted by general relativity even on large astronomical scales.

This experiment provides the most precise and robust test of gravity on such large scales to date, and which rules out some alternative gravity theories, but not all of them.

“The Universe is an amazing place providing such lenses which we can then use as our laboratories,” said ICG Director and team member, Bob Nichol. “It is so satisfying to use the best telescopes in the world to challenge Einstein, only to find out how right he was.”

Are there any aspects of general relativity that still need large-scale testing?

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