How to Bend a Ray of Light

Without actually touching it or using mirrors

Everybody knows that light is made up of energy, and that it can pass through transparent materials and can travel only in a straight line. Wrong!

First of all, due to its wave-particle duality - made famous through the work of Albert Einstein, Louis de Broglie and many others - light can exhibit properties of both waves and particles, detectable on small scales.

Second, it doesn't always travel in a straight line. Einstein (again!) predicted that immense gravitational fields like those found in space around star clusters would bend light much as a lens would. Such a "gravitational lens" was far beyond the capacity of telescopes of the day, but now they're a useful and beautiful way to view extremely distant (and therefore old and often odd) objects.

Recently, a group of scientists in the US showed that light can be guided and manipulated at the nanometer scale by passing it through collections of tiny metal spheres, at the interaction between light and the plasmons on the surfaces of the nanoscopic spheres.

Their simulations also suggested that incident light can be confined within "plasmonic crystals" made from periodic arrays of nanoparticles. Moreover, depending on the geometry of the crystal, the light could be focused and guided.

One more thing: did you know that light exerts pressure? Light pushes on objects in its way, just as the wind would do. In fact, the pressure of light can make asteroids spin faster, acting on their irregular shapes as on the vanes of a windmill, and there are even theoretical models of spacecraft using sails powered by solar wind.

Another experiment has proven that light can be manipulated to go around a defined space and continue its path, just like a ray traveling in straight line, which could mean that a person standing in front of the object around which light bends would only see what's behind the object, not the object itself, thus effectively producing an "invisibility cloak."

So it seems that light will never cease to amaze and intrigue us, just when we thought we knew all about it.

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