Reader warning: the following article may hurt your brain.
Scientists in Britain have pulled off an amazing trick: they’ve tied light into a knot.
The project was led by Dr Mark Dennis of the University of Bristol. He explained that though we see beams of light as a straight line — imagine using a torch in a darkened room — the light is more accurately described as flowing like water.
The result of this flow is optical vortices, lines along which the intensity of the light beam falls to zero, meaning they are completely black and impossible to see.
However, in the same way that a hologram can manipulate light so that we see an image apparently floating in mid-air, it can also direct the flow of light, creating and controlling the optical vortices.
So how do you take this set-up and create a knot? Why, by using knot theory of course. That’s a genuine field of mathematics which aims to solve puzzles such as whether a complex knot would undo into a straight line or a loop.
There’s more to it than just playing with bits of string however: it can also help explain the way DNA strands form and can even identify chiral molecules. These are molecules which appear in two seemingly identical shapes but can’t be superimposed, as with a human’s left and right hands (hence the way both parties in a handshake must use the same hand).
Two sets of chiral molecules may have different properties, which can cause problems if they are misidentified as identical, the most notorious example being the harmful effects of Thalidomide where researchers unwittingly only tested the safe variant of the chiral molecules.
Back to the light research, the scientists used knot theory to create knotted holograms (the colored lines in the image above), which in turn manipulated a laser beam and created the optical vortices needed to knot the light (the colored patterns in the image).
The geeky question is, of course, what this means for the future of lightsaber combat. But there are practical benefits to the work: the techniques involved give us the potential for greater control over the use of lasers, which could be useful in techniques such as speed gun cameras or automatic height measurement devices.
The research is also an example of taking an idea from pure mathematics and turning it into a physical effect.