A team of scientists is claiming to have achieved the seemingly impossible: it has managed to create a nanoscale device that allows light to travel infinitely fast< But how the hell did they do it, and what does it mean?
In empty space, light travels at 300,000,000 metres per second — the maximum speed possible, according to Einstein's theory of relativity. However, in some materials — say, water or glass — it travels slower. The difference in speeds can be expressed as a ratio, which scientists refer to as the "index of refraction": basically, a measure of how much light slows down or speeds up when it passes from material to another.
But scientists like to tinker and meddle with nature, and they've been busy creating wacky materials recently that play around with the concept of refractive index. Now, a team of researchers from the FOM Institute for Atomic and Molecular Physics in Amsterdam and the University of Pennsylvania have made a material with a refractive index of zero — which means it can make light travel infinitely fast. What the...?
The device in question sounds simple: it's a rectangular bar of silicon dioxide, measuring just 85 nanometres thick and 2000 nanometres in length, surrounded by silver which light does not penetrate. However, its effects are far from straightforward.
Because of the device's size, light does some wacky stuff when it's inside the device: it bounces around, and interferes with itself to create distinctive patterns of light and dark. Above a certain frequency, the whole thing even goes dark. But at one particular frequency, the whole thing light up brightly: instead of light travelling in waves like normal, the light appears to be everywhere at once. In fact, it all moves in perfect synchronicity, which can mean only one thing: it's moving with infinite speed.
... but not beyond?
There is, however, a but coming. That but relies on a simple piece of physics, which is adeptly explained by Science:
Light has two speeds, Engheta explains. The "phase velocity" describes how fast waves of a given wavelength move, and the "group velocity" describes how fast the light conveys energy or information. Only the group velocity must stay below the speed of light in a vacuum...
In this little device, then, the scientists are observing the phase velocity hit infinity, while the group velocity staunchly follows the laws of relativity. Sigh. Still, the device itself could have its own uses. The researchers suggest that it could be used as a new kind of antenna to transmit sculpted phase fronts of data, or used in nanoscale optical circuits. Sadly, though, the device won't manage to change the world of communication as we know it: there's not going to be any instantaneous data transfer as a result of this finding. [Physical Review Letters via Science]
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