Clumped galaxies give general relativity its toughest test yet
Nearly 100 years since Albert Einstein developed general relativity, the theory has passed its toughest test yet in explaining the properties of observable Universe. The most precise measurements to date of the strength of gravitational interactions between distant galaxies show perfect consistency with general relativity’s predictions. The results will be presented by Dr Lado Samushia at the National Astronomy Meeting 2014 in Portsmouth on Wednesday 25 June.
Samushia and his colleagues analysed more than 600,000 galaxies from the Sloan Digital Sky Survey III (SDSS-III) Baryon Oscillations Spectroscopic Survey (BOSS) catalogue to come up with a measurement of how much galaxies clump together within the vast volume that they occupy.
"Whilst the Cosmological Principle tells us that the Universe should have same properties in every direction, observations do not match this picture," explains Samushia, of the Institute of Cosmology and Gravitation at the University of Portsmouth. "Because galaxies are themselves parts of larger structures that are growing, they tend to 'infall' towards each other. This infall gives an apparent effect that we only see in the direction towards us, because of the way in which we observe the galaxies."
Using the observed distortions in galaxy positions, the team were able to measure the strength of gravity with a precision of 6 per cent, the strongest constraint of its kind as yet. The measurements turned out to be perfectly consistent with the predictions of Einstein’s general relativity theory.
"Gravity is the main driving force behind the growth of structure in the Universe. According to general relativity, gravity is a manifestation of the space-time curvature – massive objects curve the space-time around them, which affects the movement of other objects around them. It’s a very elegant theory that has been successful in explaining the outcomes of many experiments, however it is not the only theory of gravity," explained Samushia. "Theoretical physicists have proposed many alternative theories and modifications of general relativity and the challenge for observational physicists is to test the alternative theories with ever increasing precision."
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Dr Robert Massey
Dr Keith Smith
Dr Lado Samushia
The research has been published in Samushia et al, "The Clustering of Galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS): measuring growth rate and geometry", Monthly Notices of the Royal Astronomical Society vol. 439, p. 3504, 2014. A preprint of the paper is available.
Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. The SDSS-III web site is http://www.sdss3.org/.
SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, University of Cambridge, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University.
Notes for editors
The RAS National Astronomy Meeting (NAM 2014) will bring together more than 600 astronomers, space scientists and solar physicists for a conference running from 23 to 26 June in Portsmouth. NAM 2014, the largest regular professional astronomy event in the UK, will be held in conjunction with the UK Solar Physics (UKSP), Magnetosphere Ionosphere Solar-Terrestrial physics (MIST) and UK Cosmology (UKCosmo) meetings. The conference is principally sponsored by the Royal Astronomical Society (RAS), the Science and Technology Facilities Council (STFC) and the University of Portsmouth. Meeting arrangements and a full and up to date schedule of the scientific programme can be found on the official website and via Twitter.
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