Astrophysicists confirm cornerstone of Einstein’s Theory of Relativity

An international collaboration of scientists has recorded the most accurate confirmation to date for one of the cornerstones of Einstein’s theory of general relativity, ‘the universality of free fall

An international collaboration of scientists has recorded the most accurate confirmation to date for one of the cornerstones of Einstein’s theory of general relativity, ‘the universality of free fall’.

The new research shows that the theory holds for strongly self-gravitating objects such as neutron stars. Using a radio telescope, scientists can very accurately observe the signal produced by pulsars, a type of neutron star and test the validity of Einstein’s theory of gravity for these extreme objects. In particular, the team analysed the signals from a pulsar named ‘PSR J0337+1715’ recorded by the large radio telescope of Nançay, located in the heart of Sologne (France).

The universality of free fall principle states that two bodies dropped in a gravitational field undergo the very same acceleration independently of their composition. This was first demonstrated by Galileo who famously would have dropped objects of different masses from the top of Pisa's tower to verify that they both reach the ground simultaneously.

This principle is also at the heart of Einstein's theory of general relativity. However, some hints such as the inconsistency between quantum mechanics and general relativity, or the conundrum of the domination of dark matter and dark energy in the composition of the Universe, have led many physicists to believe that general relativity might not be, after all, the ultimate theory of gravity.

The observations of Pulsar J0337+1715, which is a neutron star with a stellar core 1.44 times the mass of the Sun that has collapsed into a sphere of only 25km in diameter, shows that it orbits two white-dwarf stars which have a much weaker gravity field. The findings, published today in the journal Astronomy and Astrophysics, demonstrate the universality of free fall principle to be correct.

Dr Guillaume Voisin from The University of Manchester who led the research said: “The pulsar emits a beam of radio waves which sweeps across space. At each turn this creates a flash of radio light which is recorded with high accuracy by Nançay's radio telescope. As the pulsar moves on its orbit, the light arrival time at Earth is shifted. It is the accurate measurement and mathematical modelling, down to a nanosecond accuracy, of these times of arrival that allows scientists to infer with exquisite precision the motion of the star.

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