Strong equivalence principle put to test

In 1907, Einstein established the equivalence principle to explain why we feel weight, which stated, "the effects of gravity are exactly equivalent to the effects of acceleration" (Cosmic Perspective). The strong equivalence principle goes even further to say that all objects accelerate the same way even if they hold themselves together with their own gravity.

Now, astronomers have discovered a unique three-body system out in space that can put this theory to the test.

The triple-star system that is 4,200 light years from Earth consists of a millisecond pulsar orbiting a white dwarf, which both orbit a second white dwarf. A pulsar forms when a star explodes in a massive supernova, and the remaining core is left over as a neutron star. When this star spins, it's a pulsar; when it spins incredibly fast, it becomes a millisecond pulsar. This observed millisecond pulsar spins 366 times per second.

What astronomers are now trying to discover is if the gravitational self-energy of the stars have any effect on how they accelerate. They are now looking for any deviations in the pulses that are sent to Earth, which would reveal the relative locations of each star, how much they are accelerating and the gravitational effect the outer white dwarf has on the inner white dwarf and pulsar (which, according to Einstein's equivalence principle, should be the same).

The pulsar (left foreground), orbits the inner white dwarf (center) which both orbit the outer white dwarf (top right) [Source space.com]

In the past, astronomers have tried to observed equivalence principle violations by observing the relationship between the Moon, Sun and Earth. The only problem was that the none of the objects in our system are strongly self-gravitating, so there was doubt when the astronomers came up with no evidence of a deviation. The pulsar, however, is larger than the Earth in both size and self-gravity, which could be the difference in discovering variance in pulses.

If Einstein's theory to be proven false, it would mean that the outer star's gravitational effects would vary with the other two stars -- a breakthrough in gravitational research.

Scott Ransom of the National Radio Astronomy Observatory expects the results in a year.

"If I was going to hope, I would hope that show that [the equivalence principle is] wrong," he said. "That would be really a great thing to move science forward."

I agree with Ransom. It is necessary for theories to have some sort of invalidation because it allows new questions to be asked, which then moves science onto bigger discoveries that form new theories as well. I think it is extremely cool that astronomers were able to discover this three-body system and now use it to their advantage to put a theory, which has been respected for 100+ years, to the test.








Sources:
http://www.space.com/24190-pulsar-gravity-einstein-general-relativity.html
http://physicsworld.com/cws/article/news/2014/jan/06/pulsar-and-companions-will-put-general-relativity-to-the-test
The Cosmic Perspective (Seventh Edition)