Einstein's theory of relativity passes its most difficult test to date

Einstein's theory of general relativity has passed its toughest test with flying colors, reports a new study

General Relativity Proposed by the Great Physicist in 1916, argues that the gravity is a consequence of the flexibility inherent in space-time: massive objects deform the cosmic tissue, creating a kind of well around which other bodies revolve

Like all scientific theories, general relativity makes verifiable predictions. One of the most important is the "principle of equivalence" – the notion that all objects fall in the same way, regardless of their size or composition. [Einstein’s Theory of Relativity Explained (Infographic)]

Researchers have confirmed the principle of equivalence many times on Earth – and, famously, on the Moon. In 1971, Apollo 15 astronaut David Scott dropped a feather and a hammer simultaneously; both hit the gray lunar dirt at the same time. (On Earth, of course, the feather would fly to the ground much later than the hammer, having been retained by our atmosphere.)

But it is unclear whether the principle of equivalence applies in all situations – when objects are incredibly dense or massive, for example. This room for maneuver has given hope to followers of alternative theories of gravity, although these people remain in the minority.

The new study could take some of the air out of their optimism. An international team of astronomers has tested the principle of equivalence under extreme conditions: a system consisting of two superdense stellar corpses known as white dwarfs and an even denser neutron star [19659010]. These exotic objects are so named because they seem to emit radiation in regular pulsations. This is just an observer effect, however; Pulsars continually emit radiation from their poles, but astronomers' instruments only pick up these beams when they are directed to the Earth. And because the pulsars are spinning, they can direct their poles to Earth at regular intervals.

The system in question, known as PSR J0337 + 1715, is located at 4,200 light-years from Earth, in the direction of the Taurus constellation. The pulsar, which rotates 366 times per second, co-orbits inward with one of the white dwarfs; the pair revolves around a common center of mass every 1.6 terrestrial days. This duo is in a 327 day orbit with the other white dwarf, much farther away.

The pulsar contains 1.4 times the mass of the sun in a sphere the size of Amsterdam, while the inner white dwarf contains only 0.2 solar mass and concerns the size of the Earth. So, these are very different objects – but they should be drawn by the outer white dwarf in the same way if the principle of equivalence is about money.

The researchers followed the movements of the pulsar by monitoring its radio wave emissions. They did it for six years, using the Westerbork Synthesis Radio Telescope in the Netherlands, the Green Bank Telescope in West Virginia and the Arecibo Observatory in Puerto Rico

"We can explain every pulse of the neutron star from the beginning, our observations, "said Anne Archibald, a postdoctoral researcher at the University of Amsterdam and the Netherlands Institute of Radioastronomy, in a statement. And we can say its location a few hundred meters, it's a very precise track of where the neutron star was and where it goes. "

A violation of the principle equivalence would manifest itself as a distortion in the orbit of the pulsar – a difference between the trajectory of the neutron star and that of its inner white-dwarf companion.This distortion would cause the pulsar radiation would arrive at a slightly different time from what was expected

But the researchers did not detect such distortion.

"If there is a difference, there are no more than 3 parts in a million," Nina Gusinskaia, a PhD student at the University of Amsterdam, said in the same statement. "

" Now, no matter who with an alternative theory of gravity has an even narrower range of possibilities. in order to match what we saw, "added Gusinskaia." In addition, we improved the accuracy of the previous best test of gravity, both in the solar system and with other pulsars, of A factor of about 10. "

The new study was published online July 4

Follow Mike Wall on Twitter @michaeldwall and Google+. us on @Spacedotcom Facebook or Google+ Originally posted on Space.com

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