We have no complete, consistent quantum theory of gravity. However, clues from other theories indicate that the physics we know breaks down at a certain fundamental length scale: the Planck length. In particular, the Heisenberg uncertainty principle in quantum mechanics must be modified if you can’t measure position to arbitrary precision. However, length and energy are two ends of a teeter totter: to probe to small lengths requires vast energies, and the Planck length would necessitate energy far beyond anything our particle accelerators can provide—maybe ever. As a result, researchers are using other ideas for getting at quantum gravity in the lab, including a certain kind of gravitational wave detector based on a huge metal bar.

When theory is silent, experiment must step in. A new paper analyzed results from the AURIGA gravitational wave experiment to check for deviations from standard quantum mechanics in the vibrations of a massive metal bar at cryogenic temperatures. The AURIGA results showed no deviation from standard quantum physics, yielding an upper bound on the energy of quantum gravity modifications. The experimenters concluded that the theorists needed to get back to work so that the experimenters have a better idea of what to expect. [Read more….]

(Alas, the excellent title for this article was not my idea.)

Speak softly and carry a 2.3-ton aluminum bar