It’s a trap’tor beam

 andrea.pacelliThey have forever been the stuff of science fiction; confined to the realms of Star Wars and Star Trek alike. Now though, tractor beams have made the leap into reality. Admittedly we are a long way from “beam me up Scotty”, but a recent discovery could have a profound effect on the medical industry and many others.

Although we have known for some time that light can be used to push objects away from the light source, the challenge of pulling them towards it has puzzled scientists for many years. Many techniques have been experimented with over the years for creating a tractor beam, or to use more scientific terminology, an optical conveyor, but these have all had very limited success.

Now though, a team of scientists from the University of St Andrews, together with the Institute of Scientific Instruments in the Czech Republic believe they may have cracked this ‘final frontier’ of science.

The origins of their discovery stretch back to the 17th century when Johannes Kepler observed that the tails of comets always point away from the Sun. From this he was able to deduce that microscopic objects experience a force when hit by a beam of light, causing them to travel in the direction of the beam.

The question facing the team at St Andrews was how to make the beam of light exert an apparently negative force on a selection of particles, so as to draw them towards the light source.

To achieve this they used a lens and an array of mirrors to focus a beam of photons, emitted by a laser, into an X shape. At the point where the beam crosses itself the photons interfere with each other and produce a standing wave. This can be used to force matter back towards the laser.

The intricacies of the experiment are of course much more complicated than this; but to think of it simply one might imagine an eddy or current in a river. Here the presence of an object such as a rock causes the water to flow against its original direction and potentially move small objects back up the river. This process is not dissimilar to that of the tractor beam.

As is often the case with such scientific developments the optical conveyor at present is only capable of working on a very small scale. However, whilst this does mean that we are a long way from being able to attract macroscopic objects, practical applications are already being talked about.

The optical conveyor created works on a microscopic scale and is able to separate groups of particles by pulling larger particles towards the light and pushing the smaller ones away. In the medical industry, such a technique could be used to sort the components of a blood sample.

NASA are also interested in the concept and are researching the use of tractor beams as a means of collecting samples from other planets, as well as removing dust from objects in space.

There is certainly considerable room for improvement in the design of tractor beams, but even in these very early days their practical uses are quite exciting and the potential for future applications even more so.

Unfortunately, the idea of a Star Trek-like reality is not yet possible, as scaling up the tractor beam to work on something like a spaceship would require a laser large enough to destroy the target – and you can’t just set a laser to stun!

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