Read more: 鈥�Crunch time for physics: What鈥檚 next?鈥�
The success of general relativity is embedded in our modern world. True, most solar system and astronomical phenomena are still calculated with Newton鈥檚 hoary theory of gravitation, but we would be nowhere without our GPS gadgets, which work only once corrected for the effects of general relativity.
General relativity has been tested with great precision within the solar system, and in binary pulsar systems where gravitational fields are very strong, but never on large scales where gravity鈥檚 pull is weak. Might the twin embarrassments of dark matter and dark energy mask general relativity鈥檚 failure there?
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Supporters of this idea have had some success. Modified Newtonian dynamics (MOND), proposed by Mordehai Milgrom of the Weizmann Institute in Rehovot, Israel, in the 1980s, relates mass to the gravity it generates in a slightly different way. It describes galaxies better and more parsimoniously than general relativity with dark matter does. Cosmological models constructed from alternative 鈥渇(R)鈥� gravitational theories behave as if they contain dark energy, even though they don鈥檛.
But no one theory holds all the cards. MOND does not handle motions of individual galaxies within clusters well. Neither does Tensor鈥搗ector鈥搒calar (TeVeS) gravity, a relativistic version of a theory I proposed in 2004. The f(R) theories do not adequately describe the anomalous galactic rotations that first led dark matter to be proposed.
We might yet strike lucky. If dark energy is the venerable cosmological constant that Einstein shoehorned into his equations of general relativity, its favoured source is vacuum energy. Gravitational fields might conceivably perturb the vacuum enough that concentrations of energy appear in and around galaxies and galaxy clusters, mimicking dark matter. It is impossible to magic up concentrations large enough from current quantum-field theories, but perhaps one day the mystery of the two dark stuffs may be dispelled by the judicious application of known quantum physics.
This article appeared in print under the headline 鈥淲hat鈥檚 Next Discard Relativity鈥�
