EIU Astro

The first observational proof of General Relativity May 31, 2009

Ninety years ago, on May 29 1919, Sir Arthur Eddington led a expedition to test the new theory of gravity, Einstein’s General Theory of Relativity.

Einstein first proposed his General Theory of Relativity in 1915. It describes how any massive object, such as the Sun, creates gravity by bending space and time around it. Everything in that space is also bent: even rays of light. Consequently, distant light sources, behind the massive object, can appear in a different position or look brighter than they would otherwise.

If you look at pictures of clusters of galaxies from the Hubble space telescope  you’ll see this effect as gravitational lensing. It’s the distortion of distant background galaxies as their light passes through the gravity of a cluster.

The warped images of distant galaxies appear as streaks of light

Back in 1919 they did not have the sensitive digital cameras that could see these faint streaks.  So in 1919, the Royal Astronomical Society (RAS) launched an expedition to the West African island of Príncipe, to observe a total solar eclipse and prove or disprove Einstein’s General Theory of Relativity. They were to measure the deflection of the position of stars very close to the sun, the object that has the biggest gravity in the solar system. In order to measure the dim stars so close to the sun they need a solar eclipse that would block out the sun’s glare to make the dim stars visible.

Eddington Eclipse

“This first observational proof of General Relativity sent shockwaves through the scientific establishment,” said Professor Ferreira. “It changed the goalposts for physics.”

It also made Einstein an instant worldwide celebrity, something that the special theory of relativity in 1905 did not. Thanks to X’s blog for pointing this out.