Back to the Future? Back to the drawing board

Reports that time travel has been proven impossible may be somewhat overstated, but it’s certainly looking unlikely.

The main argument against time travel is based on the fact that the speed of light is fixed and that nothing can travel faster: in effect, it’s the speed limit of the universe. The explanation for the limit is that it would take an infinite amount of energy for an object to accelerate to the speed of light and thus there’d be no way to take that extra step to what’s known as superluminal travel.

That limitation blocks one theory of time travel: that the effect of an event could travel faster than light, such that it appeared before the cause of the event. (Exploiting this disparity to allow time travel is a separate issue of course.)

There have been plenty of theories about how objects could travel faster than the speed of light, most of which are in mindbending territory, but there are two common themes: scientists usually describe such superluminal travel merely as “apparent” or “effective”, and they usually say it would have to involve abnormal conditions.

There have been studies of photons, the particle which is the basis of light, in which a group of photons appear to travel faster than the speed of light. However, Professor Shengwang Du of the Hong Kong University of Science and Technology, says that in this situation there’s no way for the photons to actually carry any information.

Du has now carried out experiments involving single photons. He split the main body of a photon from its optical precursor, which the BBC likens to “the wind that moves ahead of a speeding train.” He then found that in a vacuum, the precursor is still limited to the speed of light, and that the main body of the photon cannot travel faster.

Of course, the idea of time travel still has support, but it looks like we’re going to have to start literally ripping-up the space-time continuum and creating wormholes. That might seem quite a stretch in the month that NASA shuttle missions ended, but if we stick a bit of cash in a high-interest savings account now, then surely when we arrive in the future there should be enough there to pay the bills.