Two German scientists claim to have broken the speed of light with a tunnelling photon, a pair of prisms and a gap of about three feet.

According to New Scientist, Günter Nimtz and Alfons Stahlhofen from the University of Koblenz claim to have made the photon jump "instantaneously" across a barrier ranging from a few millimetres to three feet.

They started with a pair of prisms sandwiched together to make a 40cm cube. Then, they shone microwaves with a wavelength of 33cm through the prism. As they gradually moved the prisms apart, the microwaves, which had passed straight through, began to be refracted. Some of the microwave photons, however, tunnelled across the gap.

So far, so good. All in line with our expectations.

But Nimtz and Stahlhofen say the refracted photons and the tunnelling photons arrived at their respective detectors at the same time, regardless of the size of the gap. This, they claim, suggests that the tunnelling photons have jumped the gap much faster than the speed of light.

Nimtz told the magazine that the results were a violation of Einstein's theory of special relativity.

But not everyone is convinced the pair have interpreted their results correctly.

Some argue that what the scientists have observed can be explained by the so-called Hartman Effect. This predicts that "the tunneling (sic) time becomes independent of barrier length for thick enough barriers, ultimately resulting in unbounded tunneling (sic) velocities".

What this means is that single photons can appear to travel faster than the speed of light. But researchers suggest that tunnelling time should not be considered as a transit time, but rather as a "cavity lifetime".

Herbert G Winful from the University of Michigan explains in this paper that anomolously short delays in barrier tunnelling "should not be linked to a velocity since evanescent waves do not propagate".

So, Einstein is off the hook, and thus restored to his rightful place as top boffin. ®

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