A Staff Report from the Straight Dope Science Advisory Board

What's with news reports about things traveling faster than light?

October 25, 2000

Dear Straight Dope:

I'm a pretty skeptical person who has a casual interest in applied physics. I'm not the sort to put any stock in things like the flat earth society, homeopathy or anything involving sandals, bad clothes and using the word "quantum" five times in two sentences. However, I've been keeping my eye on reports that the now firmly entrenched theories of general and special relativity are flawed. I'm not yet prepared to put these on the shelf next to crystals because  … well, that skepticism keeps kicking in again. But until I get some guidance, I don't know what to think.

According to these reports, c is no longer the fastest speed known. In a forthcoming article in the journal Nature, Dr. Lijun Wang and colleagues of NEC at Princeton will detail an experiment in which they accelerated light pulses to AT LEAST THREE HUNDRED TIMES c! Furthermore, Italian scientists at the National Research Council say they have pushed microwaves to 1.25c!

Does this look promising? I'm just interested in knowing if the underlying logic is flawed, snake-oil, or a valiant step in the right direction

SDStaff Karen replies:

Don't get your hopes up, Matt — the theory of relativity has not been invalidated, and there's still no way to get your starship up to warp factor 8.

The reports of the speed of light being exceeded are misleading at best and have come in for criticism in the scientific community as being harmful to the cause. The problem is that if people believe scientists have disproven the previously unshakable tenets of relativity, they might be more prone to believing any kind of crap — like water molecules have memory that can be transmitted over the Internet. "That's what you scientists used to say about the speed of light," they'll claim.

The experiments that show these so-called faster-than-light velocities are showing the predicted phase-velocity effect well known to all students of relativity. Phase velocity can be understood in terms of an analogy: Imagine a bus hurtling down the freeway at the speed of bus. Someone in the back of the bus decides to start "The Wave." As an observer outside the bus, you see what appears to be a standing person traveling from the back of the bus to the front of the bus, causing you to think that an actual person is traveling faster than the speed of bus. In fact, no real person traveled faster than the speed of bus, they just changed their phase from sitting to standing, then back to sitting.

That's what's happening in these experiments. The actual light packet continues to travel at the speed of light, but the shape of the light wave inside the light packet changes, so it looks like a little wavelet peak is traveling from the back of the packet to the front of the packet, at a velocity faster than the speed of light. Trickery trickery. While the experiments are well respected and generally believed, the scientific reception typically has been ho-hum. Maybe that's why it had to be gussied up in the news reports.

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