Rethinking relativity: Is time out of joint? * 21 October 2009 by Rachel Courtland
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The analysis of starlight data by cosmologist Rachel Bean of Cornell University in Ithaca, New York, has generated quite a stir. Shortly after the paper was published on the pre-print physics archive, prominent physicist Sean Carroll of the California Institute of Technology in Pasadena praised Bean's research. "This is serious work by a respected cosmologist," he wrote on his blog Cosmic Variance. "Either the result is wrong, and we should be working hard to find out why, or it's right, and we're on the cusp of a revolution."
"It has caused quite a furore in astronomy circles," says Richard Massey of the Royal Observatory Edinburgh in the UK. "This paper has generated a lot of interest."
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Most astronomers, including Bean, are cautious about the results. "Nobody is yet betting money that the effect is real," says cosmologist Dragan Huterer of the University of Michigan in Ann Arbor. Various other explanations, like a bias in the technique used to estimate the distances to galaxies, now need to be ruled out.
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Whether these surveys find the effect or not, Bean hopes that her paper will generate more interest in the idea of using weak lensing to test general relativity. "I'm not putting my flag out there and saying this is a real thing," Bean says. "We need to look at more data sets. This is really just the first stage for trying to test gravity in this way."
Massey agrees: "At the moment we're in the mode of just trying to hack into general relativity to find the chinks in its armour, to find any places where it might not be working."
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Here's the blog entry by Sean Carroll mentioned above,
which has some comments by Rachel Bean:
A New Challenge to Einstein?by Sean
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So here is a new such test, courtesy of Rachel Bean of Cornell. She combines a suite of cosmological data, especially measurements of weak gravitational lensing from the Hubble Space Telescope, to see whether GR correctly describes the behavior of large-scale structure in the universe. And the surprising thing is — it doesn’t. At the 98% confidence level, Rachel finds that general relativity is inconsistent with the data. I’m not sure why we haven’t been reading about this in the science media or even on other blogs — it’s certainly a newsworthy result. Admittedly, the smart money is still that there is some tricky thing that hasn’t yet been noticed and Einstein will eventually come through the victor, but this is serious work by a respected cosmologist. Either the result is wrong, and we should be working hard to find out why, or it’s right, and we’re on the cusp of a revolution.
Here is the abstract:
A weak lensing detection of a deviation from General Relativity on cosmic scales Authors: Rachel Bean
Abstract: We consider evidence for deviations from General Relativity (GR) in the growth of large scale structure, using two parameters, γ and η, to quantify the modification. We consider the Integrated Sachs-Wolfe effect (ISW) in the WMAP Cosmic Microwave Background data, the cross-correlation between the ISW and galaxy distributions from 2MASS and SDSS surveys, and the weak lensing shear field from the Hubble Space Telescope’s COSMOS survey along with measurements of the cosmic expansion history. We find current data, driven by the COSMOS weak lensing measurements, disfavors GR on cosmic scales, preferring η < 1 at 1 < z < 2 at the 98% significance level.
Let’s see if we can’t unpack the basic idea.
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