For centuries Isaac Newton’s law of universal gravitation explained gravity on Earth. But astronomers eventually saw discrepancies in the way larger objects such as planets interacted.

Published in 1916, Einstein’s general theory of relativity proposed that gravity works on large scales because matter warps the fabric of space and time, also known as space-time.

This notion is used to explain phenomena in our solar system, such as the slight alterations in Mercury’s orbit around the sun, which Newton’s gravity could not account for.

The existence of dark matter and dark energy is based on the assumption that Einstein’s gravity is affecting galaxies located billions of light-years from Earth in the same way that it affects objects in our solar system.

Based on general relativity, scientists think dark matter exists because some cosmic objects behave like they have more mass than we can actually see.

Although until now, tests of general relativity on galactic scales have been inconclusive.

In the new study, appearing this week in the journal Reinabelle Reyes and colleagues examined data gathered from more than 70,000 bright, elliptical galaxies.

The team found that the galaxies, located up to 3.5 billion light-years from Earth, are clustered together in just the way that general relativity predicts.
“From the galaxies’ positions, we can tell how clustered they are. That gives us information about how gravity acts, because that’s what gravity does—it pulls things together,” says Reyes, of Princeton University.

By combining measurements of the galaxies’ clustering with other properties, like the galaxies’ movements relative to one another and the way they bend each other’s light, Reyes’s team calculated
EG, a quantity which physicists use when looking at objects’ expected interactions.

General relativity predicts that EG should be around 0.4 – the value of EG measured in the study was 0.39.