© bunnavit pangsuk/ShutterstockScientists have observed a bizarre phenomenon called time reversal in which light waves seem to travel backward in time.
The new experiment also shows other bizarre effects of light, such as pairs of images forming and annihilating each other.
Taken together, the results finally prove a century-old prediction made by British scientist and polymath Lord Rayleigh. The phenomenon, called time reversal, could allow researchers to develop ultra-high-speed cameras that can peer around corners and see through walls.
Backtracking sound wavesLord Rayleigh — the brilliant British physicist who discovered
the noble gas argon and explained
why the sky is blue — also made a bizarre prediction about sound waves nearly a century ago. Rayleigh reasoned that, because the speed of sound is fixed, an object traveling faster than that while spewing out sound would result in sound waves that would seem to travel in the opposite direction of the object and thus seem to be reversed in time orientation. For instance, a phonograph on a plane traveling at Mach 2, or twice
the speed of sound, would seem to play the music backward.
No scientists really doubted this notion, but there was no easy way to test it.
"Using sound, it's something that's really hard to verify and actually hear," said study co-author Daniele Faccio, a physicist at Heriot-Watt University in Scotland.
Sound travels at 761.2 mph (1,225 km/h), but that means that, to hear a 3-second clip of music going backward, a supersonic jet traveling at Mach 2 (or twice the speed of sound) would start replaying the music more than a mile from the listener's location. The scattering and absorption of the sound waves in the air would make the music completely inaudible by that time, Faccio said.
Comment: Slowly and gently increasing public awareness of brown dwarf stars may be part of a wider scientific agenda of disclosure: