Einstein’s gravity theory passes extreme test, says study published in Nature

James Marshall
July 7, 2018

Einstein's strong equivalence principle says all objects should fall the same way in a gravitational field, regardless of their composition or how dense they are.

Albert Einstein's theories on general relativity hold true even in one of the most extreme scenarios the universe can offer, according to a study. An global research team led by the Anton Pannekoek Institute of Astronomy at the University of Amsterdam, in the Netherlands, has shown that the equivalence principle, which holds that all bodies in the same gravitational field are equally accelerated, is correct.

So, for example, a hammer and a feather dropped from the same height in a vacuum will hit the ground at the same time; astronaut Dave Scott famously demonstrated this on the Moon in 1971.

This is because Einstein's principle of gravity has just been proven right by yet another major science experiment, making it increasingly hard for alternative gravity theories to demonstrate their case.

Instead, this unique star system confirmed both Galileo's theory of motion and Einstein's theory of gravity. The new research found both inner stars accelerating at very similar speeds, which fits in with the equivalence principle as explained in Einstein's general theory of relativity. That difference, these alternate theories predict, would be due to a compact object's so-called gravitational binding energy - the gravitational energy that holds it together. An global team of astronomers tested the equivalence principle under extreme conditions: a system composed of two superdense stellar corpses known as white dwarfs and an even denser neutron star.

"This remarkable system turns out to be the most precise laboratory to carry out these tests", said Lorimer, who carried out some of the Green Bank Telescope and Arecibo observations. "We don't know of any others quite like it".

"Every single time we've tested Einstein's theory of relativity so far, the results have been consistent", said team member Professor Ingrid Stairs, from the University of British Columbia.

They took more than 800 observations of the star system from Green Bank Telescope in West Virginia, the Arecibo Observatory in Puerto Rico, and the Westerbork Synthesis Radio Telescope in the Netherlands. The GBT has spent more than 400 hours observing this system, taking data and calculating how each object moves in relation to the other.

Now, nearly 80 years later, a study led by researchers from the University of Amsterdam in the Netherlands have proven that even extremely massive objects, such as superdense neutron stars, fall just like a feather. Pulsars often times spin with a precise consistency that is equal to atomic clocks on here on Earth, says the report. "As one of the most sensitive radio telescopes in the world, the GBT is primed to pick up these faint pulses of radio waves to study extreme physics", Lynch said. PSR J0337+1715 rotates 366 times per second, sending out beams of radio waves. They are made from collapsed cores of stars that have undergone supernova explosions and are the densest stars in the Universe. By tracking the trio, the scientists wanted to find out whether the neutron star and inner white dwarf were affected differently by the gravity of the outer white dwarf.

Through meticulous observations and careful calculations, the team was able to test the system's gravity using the pulses of the neutron star alone.

"If there is a difference, it is no more than three parts in a million", said Nina Gusinskaia from the University of Amsterdam in the Netherlands.

Thus, Einstein's theory of general relativity has passed the most rigorous test to date, while other alternative approaches, such as some versions of string theory, have been virtually ruled out.

Researcher have found the ideal "laboratory" to test one of the principles of Einstein's theory of relativity and proved him right one more time.

Other reports by Click Lancashire

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