Can gravitational waves be detected in ‘Millikan oil drops’?

LIGO in Hanford, Washington: Could two drops of helium beat it in the race to detect gravitational waves?

By Hamish Johnston

Experiments that search for gravitational waves tend to be very large. The LIGO detectors in the US, for example, have arms that are 4 km long.

This is because the gravitational interaction is much weaker than the electromagnetic forces that govern the detectors. As a result humongous masses and long distances are needed to produce the tiniest signal — indeed, gravitational waves have yet to be detected directly.

However, Raymond Chiao believes that gravitational waves can be detected in tiny drops of superfluid helium that are coated with a specific number of electrons.

The drops would be suspended in a strong magnetic field — a setup that conjures up the famous oil drop experiment that allowed Robert Millikan to measure the charge of the electron.

Chiao describes his experiment in a book entitled Visions of Discovery: New Light on Physics, Cosmology and Consciousness, to be published by Cambridge University Press in 2010. The book is edited by Chiao — who has a long and distinguished career in quantum optics — and includes contributions from Nobel laureates Anthony Leggett and William Phillips.

As far as I can tell, the trick in Chiao’s proposed experiment is to set the charge-to-mass ratio of the drops such that each electron corresponds to a ‘Planck mass’ quantity of helium. Objects lighter than the Planck mass tend to be governed by quantum mechanics rather than general relativity.

“Now the force of gravity is approximately 137 times stronger than the force of electricity”, he writes.

Furthermore, two such drops separated by a centimetre or so would act as a “quantum transducer” that could convert an incoming gravitational wave into an outgoing electromagnetic wave — which Chiao believes could be used to detect gravitational waves.

So what do other physicists think?

The chapter is prefaced with an editor’s note, which begins “The following chapter has been the subject of considerable controversy during the review process”.

It goes on to say that one reviewer thought Chiao’s proposal was “reasonable”, while the others “found this claim to be highly questionable”.

Apparently the problem is that “some statements in the paper may be inconsistent with the current theory of superfluids. However that theory may be wrong…” — I believe this refers to Chiao’s proposed mechanism that couples gravitational and electromagnetic waves on the surface of the drops.

One way or another, Chiao’s chapter makes for a fascinating read.