Did Scientists Really Just Break the Speed of Light?

By Jamie Condliffe on at

Today, you might read that scientists have developed a way to produce faster-than-light travel. But steady, there: we've been burnt once recently, so let's not let it happen again. Did scientists really manage to break the speed of light?

According to Einstein's special theory of relativity, light traveling in a vacuum is the universal speed limit. That's a well-established rule—but it is one that scientists like to flirt with the idea of breaking.

Including researchers at the US National Institute of Standards and Technology (NIST), who have been trying to exploit a loophole in the rule, that could see something travel faster than light. That thing is information, and the loophole relies on forcing one pulse to propagate through a second one. If the second pulse is moving at a speed close to the speed of light, it should in theory be possible to make the first one travel faster than the speed of light.

Which is, pretty much, exactly what the researchers from NIST have done, if you read their paper in Physical Review Letters. They've taken that concept—which is itself old and done before, but so badly that the results were really rather scrappy—and given it another go.

The NIST scientists used a concept called four-wave mixing. That sounds complex, but it's really just a way of combining signals of different frequencies in such a way as to produce a new signal containing four separate frequencies. In fact, they took 200-nanosecond-long "seed" pulses of laser light and aimed them into a heated cell containing rubidium vapour. Then, they pumped in a second beam at a different frequency. The two beams interacted with each other, and the vapor, to produce a new pulse which itself contained a second, moving pulse. Their results suggest that the pulse-within-a-pulse went faster the speed of light.

Great! Wait, no. Not that great. The pulse is incredibly short-lived—it takes next to no time for it to propagate the length of its carrier pulse—and it can never really do anything. It starts, then stops. In fact, it's little more than a little mathematical trick. What the scientists are observing here is the propagation of a small scrap of information—so nothing with any matter—moving slightly faster than the speed of light.

While it's tempting to say that this could represent the dawn of data that can move faster than light, that's not really true either. You see, this in fact quantum data: it's not a neat binary bit, a one or a zero, but a blurry mess that could take any value. What's more, we have no control over it.

So yes, something did move faster than the speed of light and it was, this time, real. And, yes, it is impressive in a very abstract physical science kinda way. But it's not going to turn Einstein's theory on its head, nor revolutionise physics. So I wouldn't get too excited. [Physical Review Letters via The Register]

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