The Earth does not simply rotate around its axis. It drags space-time itself along with it, like a spoon slowly turning in thick honey. This effect, predicted by the general theory of relativity and known as frame dragging or the Lense-Thirring effect, has until now been detected only with the help of satellites, by observing their orbits over years.
Now physicists have proposed a way to measure the very same thing right in the laboratory — in a matter of seconds. A group of researchers led by Kai-Isaac Ellers of the University of California, Berkeley, described in Physical Review Letters the design of a quantum sensor based on superfluid helium. The device is a ring-shaped microchannel with a nanoporous partition, where helium at ultralow temperatures loses all internal friction and forms an analogue of a Josephson junction.
Any rotation, however negligible, alters the quantum properties of the flowing helium. These changes are easily read out through the junction, turning the sensor into an ultrasensitive gyrometer. According to the authors' calculations, the accuracy of measuring the frame-dragging effect will reach 0,2 percent — the same as that of the best satellite experiments, but in one second instead of many years of observations.
Such speed opens up new possibilities. The laboratory instrument will make it possible not only to confirm Einstein's predictions with high accuracy, but also to test alternative theories of gravity, in which the frame-dragging effect may differ. Moreover, the technology will find application in navigation, geophysics and, possibly, in future experiments to probe the quantum nature of gravity.
Bringing the idea to fruition will still require serious engineering work, yet modern technologies already make it possible to create the necessary conditions. If the plan can be realized, humanity will gain a compact tool for studying the subtlest manifestations of the general theory of relativity without launching expensive satellites.
