Two physicists in Germany claim they have broken the speed of light, an accomplishment which, according to Albert Einstein's special theory of relativity, is impossible. The claim is made by Gunter Nimtz and Alfons Stahlhofen, both of the University of Koblenz.

The pair claim that in an experiment they set up, microwave photons travelled "instantaneously" between two prisms that had been moved apart to distances ranging from a few millimetres to three feet. According to Einstein's calculations, to propel an object faster than the speed of light - which is about 186,000 miles per second - would require an infinite amount of energy.

The scientists originally began experimenting with the prisms placed against each other to form a 40 cm cube. They then passed microwaves of wavelength 30 cm through the prisms. As they moved the prisms apart, some of them were refracted, and some, as predicted, began quantum tunnelling across the gap. The scientists say that both the refracted and the tunneling particles reached the detectors set up for each at the same time, suggesting the tunnelling photons had jumped the gap at significantly beyond the speed of light.

The duo were conducting various experiments in quantum tunnelling, a bizarre phenomenon which allows sub-atomic particles to behave in manners that are apparently impossible. Quantum tunnelling occurs when photons cross over a seemingly uncrossable barrier. However, Nimtz said of his discovery to the New Scientist magazine "For the time being, this is the only violation of special relativity that I know of."

Some sources believe the pair misinterpreted their results, citing another phenomenon, known as the Hartman Effect. This effect predicts that "the tunnelling (sic) time becomes independent of barrier length for thick enough barriers, ultimately resulting in unbounded tunnelling (sic) velocities", i.e. an individual photon may appear to be travelling at significantly beyond the speed of light. And research published by Herbert G Winful of the University of Michigan casts further doubt on the claim, stating that unusually brief delays in tunneling "should not be linked to a velocity since evanescent waves do not propagate".