Wednesday, September 23, 2009
340 West Hall
Speaker: Jacob Bekenstein (Hebrew University of Jerusalem& Institute for Advanced Study, Princeton)
With his argument that very large numbers are not natural, Dirac (1937) opened Pandora's Box of variability of the physical constants. One escapee from the box is the variable fine-structure "constant", alpha. First incorporated into a scalar-tensor theory by Jordan (1937), variable alpha was linked by Dicke (1964) to a violation of the venerable weak equivalence principle. Gamow's (1967) proposal that alpha tracks the universe's age spawned a veritable industry bent on setting bounds on alpha's temporal variability from variegated astronomical, geophysical and laboratory measurements. To critically compare two such bounds based on different techniques one needs a theory. This talk will illuminate the simplest consistent theory of alpha variability. With it I reexamine the issue of violation of the equivalence principle; the violation is expected to be much smaller than the widely accepted argument suggests. This has consequences both for planned space tests of the equivalence principle and for estimates of temporal alpha variability in the expanding universe.