Now light would lose to light, if it were to race against itself. Researchers have now made light propagate through special media at speeds faster than the conventional speed of light (a mind-boggling 299,792,458 m/s). However, Einstein and his many fans need not worry; this faster-than-light propagation doesn’t violate relativity, which states that the speed of light is the fastest speed possible.
Building Packets of Waves
The secret to such a feat is the building up of wave-packets. Wave-packets are exactly what their name suggests packets of waves. Interference of waves is the key phenomenon.
Waves have the unique property to interfere, whether it be constructively or destructively. When two waves overlap, peak to peak, the overlap or interference is maximal. This is called constructive interference. When the waves overlap, such that peak and trough coincide, they cancel each other’s contribution out, giving destructive interference.
By selecting a large number of waves (theoretically, an infinite number), differing from each other by fraction of their wavelengths, a wave-packet can be built, such that it has a central peak, smoothly falling off on either sides. The waves interfere constructively near the peak and destructively further away from it. Thus, we arrive at an important conclusion: The constituent waves determine the position and magnitude of the peak of the wave-packet, through their mutual interference.
If we could find a material, which would selectively allow only certain wavelengths to go through, a wave-packet can be suddenly deformed when it enters a medium. Also, we could shift the location of the peak.
Shifting peaks and moving fast
Enter Vitaliy Lomakin of the University of California, San Diego and his colleagues at the Public University of Navarre in Pamplona, Spain. They used Teflon as the propagating medium. Microwave radiation was made to pass through a copper disc sandwiched between two Teflon discs. It was noticed that the wave jumps forward, emerging from the back Teflon plate, before it enters the metal plate. The team reported sending 10% of the light 10 picoseconds earlier than usual.
Einstein still stands tall
Physicists interpret the postulate of relativity to mean that information cannot be transferred faster than light. Here, no useful information can be transferred for that the entire wave-packet has to be transferred, not some part of it. The wave-packet is highly distorted, and also markedly reduced. Causality is not violated.
Einstein still stands, even though light can now travel faster than itself. The findings will soon be published in the prestigious Physical Review Letters.