Can photons move faster than the speed of light? You wouldn’t think so, not if the name ‘Einstein’ has resonance, but Günter Nimtz and Alfons Stahlhofen (University of Koblenz) have been working on so-called quantum tunneling, joining two glass prisms and feeding microwave light into them. Tunneling occurs when a particle jumps an apparently uncrossable gap, and that’s just what the team’s microwave photons appear to have done, at least a few of them, when the prisms were separated. The bulk of the microwaves were reflected by the first prism.
New Scientist will soon be reporting on this story, which picks up on the German researchers’ recent paper. The tunneling photons seem to have reached the detector at the same time that their non-tunneling cousins did, suggesting movement far beyond the speed of light. The tunneling time evidently did not change when the prisms were pulled further apart.
Is this a violaton of relativity? Perhaps not. Note this from the New Scientist story, discussing Aephraim Steinberg’s views on the matter as an expert in quantum optics at the University of Toronto:
Steinberg explains Nimtz and Stahlhofen’s observations by way of analogy with a 20-car bullet train departing Chicago for New York. The stopwatch starts when the centre of the train leaves the station, but the train leaves cars behind at each stop. So when the train arrives in New York, now comprising only two cars, its centre has moved ahead, although the train itself hasn’t exceeded its reported speed.
“If you’re standing at the two stations, looking at your watch, it seems to you these people have broken the speed limit,” Steinberg says. “They’ve got there faster than they should have, but it just happens that the only ones you see arrive are in the front car. So they had that head start, but they were never travelling especially fast.”
The paper (short, dense and containing a diagram of the experimental set-up) is Nimtz and Stalhofen, “Macroscopic violation of special relativity,” available online. I’ll post a link to the New Scientist story as soon as it goes online. In the interim, here’s the Telegraph‘s brief coverage.
Addendum: The New Scientist story is here, though only available in its entirety to subscribers.