In one minute

Ralf Schützhold and William Unruh respond to the report of an analogue Hawking effect from light pulses in silica glass. They list what a Hawking effect requires, including thermal radiation from a time-independent system driven by exponential tearing of waves at a horizon. Of five conditions, only the negative energy beyond the phase horizon applies, so the experiment is an important step towards observing Hawking radiation. The pulse has phase horizons but no group-velocity horizon, and the estimated Hawking temperature and photon numbers fall orders of magnitude short of the observed signal. They praise the technique and expect such a setup may well give the first observation of spontaneous Hawking emission in an analogue system.

Comment on 'Hawking Radiation from Ultrashort Laser Pulse Filaments'