Comment on: Hawking Radiation from Ultrashort Laser Pulse Filaments

Understand

In a recent paper Belgiorno {\em et al} claimed to have observed the analog of the Hawking effect because of the detection of radiation in a frequency range in which what they called "phase horizons" existed.

• They created rapidly moving pulses of light in a silica glass whose Kerr effect altered the refractive index to create those horizons.
• Unfortunately, while the observations are very interesting, the cause of the radiation is not understood, and we feel it is not justified to call this a detection of the Hawking effect in an analog system.