Imagine being able to peek inside a black hole and even perform experiments there. It may not be as far-fetched as it sounds, thanks to a team which claims to have simulated a black hole’s event horizon in the lab.
Ulf Leonhardt at the University of St Andrews, UK, and his colleagues accomplished the feat by firing lasers down an optical fibre, exploiting the fact that different wavelengths of light move at different speeds within an optical fibre. They first shot a relatively slowmoving laser pulse through the fibre, and then sent a faster “probe wave” chasing after it. The first pulse distorts the optical properties of the fibre simply by travelling through it. This distortion forces the speedy probe wave to slow down dramatically when it catches up with the slower pulse and tries to move through it. In fact, the probe wave becomes trapped and can never overtake the pulse’s leading edge, which effectively becomes a black hole event horizon, beyond which light cannot escape.
This “laser black hole” could allow physicists to examine what happens to light on both sides of a event horizon – “a feat that is utterly impossible in astrophysics”, the authors note in their paper. Cosmologists have already worked out exactly how light should change frequency as it approaches an event horizon – from the outside or the inside of a black hole – and sure enough, the team observed exactly these shifts in their experiment. It should also be possible to use the artificial event horizon to help test whether anything can escape from a black hole. In the 1970s, Stephen Hawking predicted that hot black holes could radiate particles, dubbed Hawking radiation, but it’s tough to check this using telescopes, because they’d be swamped by noise. The team calculates that their laser black hole shares this property, and that it will “radiate” photons if it heats up to about 1000 °C. Ray Rivers at Imperial College London is impressed by the work’s potential to test astrophysical phenomena: “They’ve done some clever stuff to give us a chance of seeing Hawking radiation for the first time.” Leonhardt presented the results at the Cosmology Meets Condensed Matter meeting in London last month.