Shape from sound: New methods to probe the universe

As the uni­verse expands, it is con­tin­u­ally sub­jected to energy shifts, or "quan­tum fluc­tu­a­tions," that send out lit­tle pulses of "sound" into the fab­ric of space­time. In fact, the uni­verse is thought to have sprung from just such an energy shift. A recent paper in the jour­nal Phys­i­cal Review Let­ters reports a new math­e­mat­i­cal tool that should allow one to use these sounds to help reveal the shape of the uni­verse. The authors recon­sider an old ques­tion in spec­tral geom­e­try that asks, roughly, to what extent can the shape of a thing be known from the sound of its acoustic vibra­tions? The researchers approached this prob­lem by break­ing it down into small work­able pieces, accord­ing to author Tejal Bhamre, a Prince­ton Uni­ver­sity grad­u­ate stu­dent in the Depart­ment of Physics.

To under­stand the authors' method, con­sider a vase. If one taps a vase with a spoon, it will make a sound that is char­ac­ter­is­tic of its shape. Sim­i­larly, the tech­nique Bhamre and her coau­thors devel­oped could, in prin­ci­ple, deter­mine the shape of space­time from the per­pet­ual ring­ing caused by quan­tum fluctuations.

The researchers' tech­nique also pro­vides a unique con­nec­tion between the two pil­lars of mod­ern physics -- quan­tum the­ory and gen­eral rel­a­tiv­ity -- by using vibra­tional wave­lengths to define the geo­met­ric prop­erty that is spacetime.

Bhamre worked with coau­thors David Aasen, a physics grad­u­ate stu­dent at Cal­tech, and Achim Kempf, a Water­loo Uni­ver­sity pro­fes­sor of physics of information.

Source: Princeton University