The cornerstone of physics is the universality of the laws of nature. From your back garden to far-away galaxies, everything moves, shakes, and shines according to the same principles. Obviously, we are here and not there, so scientists have to come up with ingenious ways to test theories at a distance.
An international team led by Japanese researchers has now been able to test Einstein’s theory of general relativity up to 13 billion light-years from Earth, and they found that the theory is still valid.
The test involved constructing a 3D map of 2,783 distant galaxies and looking at how they appeared to be distributed according to their redshift. Redshift is a quantity used in astrophysics as a proxy for the distance of an object. If a galaxy appears to be moving away from us due to the expansion of the universe, its light will appear to be shifted towards the red side of the spectrum.
Galaxies in large groups can have high velocities, and this can generate some distortions in their redshifts as adoppler shift is added to the effect caused by the cosmic expansion. When galaxies are mapped in terms of their redshift, their distribution is often elongated towards the observer – an effect that has garnered the phenomenon the nickname "Fingers of God."
A 3D map of the Universe spanning 12 to 14.5 billion light-years. NAOJ; Partial data supplied by: CFHT, SDSS
The presence of the distortion is strongly dependent on gravity and how matter is distributed in the universe, making it a perfect testing ground for general relativity. The measurement in the study, published in Publications of the Astronomical Society of Japan, is consistent with the prediction from general relativity.
“We tested the theory of general relativity further than anyone else ever has. It’s a privilege to be able to publish our results 100 years after Einstein proposed his theory,” said lead author Teppei Okumura in a statement.
Although relativity has passed with flying colors, it is not a complete theory. General relativity is not compatible with quantum mechanics, which leads to problems in extreme scenarios like black holes or the Big Bang.
There are also alternative hypotheses to general relativity that are constructed to explain away dark matter and dark energy, and spotting a violation of general relativity could hint at one of these ideas being valid. But relativity is hard to disprove and it has, once again, survived the scrutiny of scientists.
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