Physicists have grown accustomed to receiving the occasional crackpot letter or email from armchair theorists claiming that "EINSTEIN WAS WRONG!!!" And now the recipients of those missives have a bit more evidence in their favor. Earlier this month, a team of physicists from UC-Berkeley, University of Zurich, and Princeton University announced that their analysis of more than 70,000 galaxies demonstrates that the theory of general relativity holds true -- now up to about 3.5 billion light years from Earth.
Specifically, Einstein predicted that because gravity warps space-time, light will bend whenever it passes near any object with a lot of mass, like the core of a galaxy. And that prediction has been verified again and again. And again.
No doubt some are wondering: this is news? Well, it might not seem particularly earth-shattering, but scientists aren't the sort to rest on their laurels. Einstein proposed general relativity nearly a century ago, and physicists have been testing it ever since, looking for any possible violation -- because even a tiny violation would be, as Richard Feynman was fond of saying, "IN-teresting!"
Most tests of relativity to date have been at the scale of the solar system; putting it to the test at the galactic scale has been a bit more problematic, with findings inconclusive. The Berkeley/Princeton/Zurich team looked at galaxy clusters using data from the Sloan Digital Sky Survey (the scientific gift that keeps on giving), using an innovative new approach: analyzing their velocities and how much light was distorted as it passed through any intervening matter -- an effect known as weak lensing that can make a round galaxy look as if it's shaped more like an ellipse.
The latest conclusion also has some important implications for competing cosmological models -- the valid variety, put forth by bona fide physicists, as opposed to the fringe contingent -- specifically those that seek to provide an alternative to requiring the existence of dark matter to explain observational data. The alternatives include something called tensor-vector-scalar gravity (TeVeS), a tweaking of standard general relativity to take dark matter out of the equation.
The weak lensing approach taken by the Berkeley/Princeton/Zurich team means they were able to compare their analysis with the predictions of various competing theories, including both the cold dark matter model of general relativity (which also takes into account a cosmological constant to account for dark energy) and TeVeS. And the results ruled out the latter.
Which is not to say this is the final word on the matter, because science marches on. The next step is increasing the sample size. The team is looking forward to expanding their analysis to as many as a million galaxies when the Baryon Oscillation Spectroscopic Survey (BOSS) comes online in five years or so. And there's more projects on the horizon after that. So there's a shred of silver lining for those armchair physicists with questionable theories: Einstein could still be wrong.
Tags: Astrophysics, Cosmology, ESA, Galaxies
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