Tue, Nov 17, 2009
The Straits Times
Tripping the light fantastic

By Andy Ho, Senior Writer

SCIENTISTS are supposed to be cool, calm people engaged in the dispassionate pursuit of truth.

So one can hardly imagine them maliciously sabotaging the career of, and uttering calumnies against, a colleague for holding an unorthodox view - and not in climate science either.

In his quirky but candid book, Faster Than The Speed Of Light, Dr Joao Magueijo paints just such a picture of the rarefied world of theoretical physics. In 1999, the Imperial College don had upset his peers with a paper arguing that the speed of light was 60 times faster at the Big Bang than it is now.

That is, light has slowed down since then - which means, obviously, that the speed of light can vary. But this simply went against a key tenet of Albert Einstein's special theory of relativity, that the speed of light in a vacuum, at 299,792,458 metres per second, is the universal limit to how fast anything can travel.

Travelling faster would turn back time: You would arrive at your destination before you even left; an effect would come prior to its own cause, which is nonsensical. For daring to say as much, Dr Magueijo suffered much disdain and condescension from peers who engaged in churlish politicking against him.

Yet, if it could indeed be shown that this ultimate speed barrier may be broken, then Einstein's theory and the theoretical structure of traditional physics would be shaken to its foundations. Many would see their life work in shreds. Hence the raw emotions and pettiness this Spaniard evoked.

Still, Dr Magueijo was not without his supporters, for his theory would help solve puzzles like how there could be 10 dimensions in the fabric of space. In 2005, his theory received experimental support of sorts from a report in Nature.

US scientists sent a pulse of laser light through a chamber of cesium vapour so fast that the light pulse's main part left the chamber before all parts of the pulse had even finished entering it. Thus parts of the light pulse seemed to have travelled faster than the speed of light.

Also in 2005, top physics journal Physical Review Letters published a report from Italian researchers who used curved mirrors to push light 5 to 7 per cent faster than - well, the speed of light

Dr Magueijo's theory of the varying speed of light could have some practical uses in telecommunication. However, it is slowing light down that may be more important than speeding it up.

At present, data can already be transmitted through fibre optics at the speed of light. But these light signals must be transformed into slow electrical signals before their destination's address can be read. If light is slowed down instead so that this address can be read without having to make that transformation, then the whole process could be much more efficient.

However, when light packets (photons) are slowed down, most of them lose their shape and break up. This means that the signal that one is trying to send would be lost. How to slow light down without distortion is the focus of research now.

In 2007, US scientists reported in Nature that they had managed to slow light down and even stop it (using gases, not solids). They piled the light up, stored it in a tiny vacuum chamber where it stayed quiescent and even vanished after they extinguished the light. Later, they were able to resurrect the light pulse inside a completely different vacuum chamber placed 0.2 mm away.

Both chambers held the Bose-Einstein condensate, a cloud of ultracold atoms that act collectively as one entity. Laser light shot into the first chamber, being made up of photons, intrinsically carried information about the shape, amplitude and phase of these photons. It was found that this information became imprinted on the atoms of matter in the first chamber because the photons cause the atoms to enter into two states of energy simultaneously.

The laser was then switched off but not before energy from the photons had propelled the atoms of matter out of the first chamber across a gap of 0.2 mm - a great distance for atoms to leap - into the second. Once inside the second chamber, these atoms shifted their energy levels back, causing the release of photons with exactly the same characteristics (information) as the original ones.

What this means is that one can store light (and its information) inside matter, then recall that information and transmit it along unchanged in the form of matter.

However, this work cannot yet be directly applied to improving optical communication since the media used was Bose-Einstein condensates, not simple off-the-shelf optical fibres. But it did prove, in principle, that light could be used as a new kind of memory unit: By stopping light, conceptually speaking, a quantum bit of information was stored.

Since changing the first light signal (and its information) would produce a different matter copy of that light, it became clear that quantum information could also be processed.

Finally, transferring a changed light pulse into matter, sending the matter on its way and then changing that matter back again into a new light pulse without losing any information suggested that an efficient way of processing optical information could be in the offing.

Notice also that matter was transported across space in little bits and pieces - using light. Beam me up, Scotty?

This article was first published in The Straits Times.

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