Can a pendulum swing in space? It might if it is quantum powered - a fact that could be exploited to build tiny timepieces that exploit an unusual force that occurs on the smallest scale in a vacuum.

The Casimir force is an effect that pushes two parallel conducting plates together when the distance between them is tiny. The force arises because the gap between the plates is filled with virtual photons popping in and out of existence.

As the plates come closer together, fewer photons can fit within the gap. On the outer sides of the plates, however, the photons are unconstrained, causing a pressure difference that pushes the plates together.

Now Habibollah Razmi and Mah Abdollahi from the University of Qom, Iran, hope to exploit a similar force that occurs between a polarised atom and a flat conducting plate.

The plan is to hang the polarized atom at the end of a short string of atoms above a conducting plate and set it swinging. The device then works like an ordinary pendulum, but with the Casimir-like force playing the role of gravity.

Razmi told New Scientist that there shouldn't be any need to worry about forces such as friction or gravity: "At microscopic levels the usual macroscopic forces are not important and are fundamentally not present."

The researchers call their device a Casimir Atomic Pendulum and calculate that it should have a period of about a tenth of a microsecond. They say that such a device could possibly be built with today's technology.

Since the force that would power the pendulum is the same everywhere in the universe, Roberto Onofrio, from Dartmouth College in Hanover, New Hampshire, US, and Giuseppe Ruoso from the Legnaro INFN National Laboratory, Padova, believe a vacuum clock could be useful for space applications, perhaps as a miniaturised clock for components of satellites.

"Such a vacuum clock might compete with an atomic clock or a quartz crystal clock, if the oscillations were found to be stable," says Thomas Valone from the Integrity Research Centre, Maryland, US.

However he points out that since the pendulum is only a string of atoms, the length of the "tick" might vary if the string were to twist or stretch.

Journal reference: Physics Letters A (DOI:link)