Einstein Passes, Again

Most precise test yet of Einstein’s gravitational redshift

When the cesium atom matter wave enters the experiment, it encounters a carefully tuned flash of laser light. The laws of quantum mechanics step in, and each cesium atom enters two alternate realities, Müller said. In one, the laser has pushed the atom up one-tenth of a millimeter – 4/1000 of an inch – giving it a tiny boost out of Earth’s gravitational field. In the other, the atom remains unmoved inside Earth’s gravitational well, where time flies by less quickly.

While the frequency of cesium matter waves is too high to measure, Müller and his colleagues used the interference between the cesium matter waves in the alternate realities to measure the resulting difference between their oscillations, and thus the redshift.

This is the UC Berkeley press release, and if one can ignore the use of the “many worlds” reference of alternate realities, is otherwise pretty good. It also includes some laser table porn which has been filtered out of the other stories I’ve run across. I’ve only had a chance to glance at the article, but there’s a lot of interesting physics in there that is not mentioned in the press release, or in the Nature summary story that ran in addition to the article (and was somewhat disappointing in terms of how it recapped the experiment).

The basic experiment is a decade old; the original idea was to measure the local value of g, because the two paths of the atoms have an energy difference of PE = mgh, and that gives you a phase difference for the two paths. The trick here is in reinterpreting the results in terms of relativity. I’ll try and summarize the details soon.