Einstein's general theory of relativity came under attack last week when physicists reported that neutrinos can travel faster than light. However, a team of Denmark astrophysicists has claimed to have validated Einstein's theory by studying the cosmic world.

Theory of Relativity and Gravitational Redshifting

Einstein's theory of relativity encompasses two theories - Special and General theory of relativity. Special theory of relativity which deals with space-time is now being reviewed by the CERN scientists. The general theory of relativity of late, however, gained more importance with the astrophysicists who proved that Einstein's theory is still correct in the cosmic world.

According to the general theory of relativity which is a metric theory of gravitation, gravity of any particle affects space-time deeply by warping it. The theory was validated previously by studying the sun and other small stars in the solar system but now researchers in Denmark have proved it on a greater scale, by studying the center of a galaxy cluster.

A team of Niels Bohr Institute astrophysicists, led by Radek Wojtak, studied the basic assumption of the general theory of relativity: light loses energy while escaping the gravitational field created by the celestial bodies, the stronger the gravity pull, the more the light's loss of energy. Since light's energy is related to wavelength, it will create longer wavelength while emitting from the center of the galaxy as gravity is stronger in the center than in the galaxy edge. Therefore, wavelength of light will be shorter when it emits from the edge. The process is known as gravitational redshifting.

To validate Einstein's theory, Wojtak and his team collected data from about 8,000 galaxy clusters by the Sloan Digital Sky Survey and performed a statistical analysis.

The motto of the work was to detect gravitational redshift by studying the properties of the redshift distribution of galaxies in clusters rather than by looking at redshifts of individual galaxies separately, Wojtak explains.

We could measure small differences in the redshift of the galaxies and see that the light from galaxies in the middle of a cluster had to 'crawl' out through the gravitational field, while it was easier for the light from the outlying galaxies to emerge, Wojtak adds.

Their research on galaxy clusters clearly shows that the redshift of the light is proportionally offset in relation to the gravitational influence from the galaxy cluster's gravity, says Wojtak. In that way our observations confirm the theory of relativity.

This is a major victory for Einstein's theory of relativity but requires further probe, believe astrophysicists worldwide.

The research also confirms the validity of the concordance model - Lambda-Cold Dark Matter - and supports dark energy of the universe.

The finding was published in Nature.

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