Hidden power

In Faccio’s lab in Edinburgh, the experiments that cram the bench-tops aim to simulate the black hole’s event horizon using intense laser pulses. By concentrating laser light into  a very small spot within a waveguide made  of a glass block, he can temporarily change  the refractive index of the glass so that it  slows down subsequent laser pulses and ultimately repels them. “What makes these analogue experiments so powerful is that from a photon or a water wave’s perspective,  it has no way of distinguishing whether it  is crossing the event horizon of a real black hole or is in a waveguide under some weird constraints,” he says. While their original motivation is to investigate esoteric questions of physics, there could be more worldly pay-offs, too. Using expertise garnered from their experiments, Faccio’s team is currently working on a way of “squeezing” pairs of entangled photons out of the vacuum, a recently discovered phenomenon called the dynamical Casimir effect. A cheap and easy source of entangled photons would be a boon for super-secure quantum communication technologies. These already use entangled photons to exchange information, but currently need bulky optical equipment to make them. Exploring and using such new phenomena are, to Faccio, another big draw of working with analogues. They can do far more than just model an aspect of the world as a model railway does: their true value lies in taking us places where we cannot go ourselves,  and telling us which of our ideas about  the real world are right, and which effects really do happen out there. “Once you’ve demonstrated that they exist,” says Faccio, “you can ask, ‘can I actually use them?’ ” So, a little more than mere idle tinkering.  ■