Speed Of Light Broken With Off Shelf Components

jukal writes "An interesting article at NewScientist.com: " Now physicists at Middle Tennessee State University have broken that speed limit over distances of nearly 120 metres, using off-the-shelf equipment costing just $500.", " it may be possible to use this reflection technique to boost electrical signal speeds in computers and telecommunications grids by more than 50 per cent. Electrons usually travel at about two-thirds of light speed in wires, slowed down as they bump into atoms. Hache says it may be possible to send usable electrical signals to near light speed. ""

Comments

Links & a question

[alienmole]

Of course, we're going to have the usual back and forth about how this isn't really breaking the speed of light, it's just the group velocity, etc. For those unfamiliar with the issue, the following links might help:

http://scienceworld.wolfram.com/physics/Superlumin al.html
http://www.weburbia.com/physics/FTL.html
http://physicsweb.org/article/world/13/9/3

The thing that really seems interesting about this is that they're doing this with cheap equipment, which will make experimenting with this a lot easier.

Can anyone explain how this would be used to increase subluminal transmission of electrical signals, as mentioned in the article? This whole group velocity thing has always seemed like a bit of an illusion to me, and none of the explanations I've seen has really clarified how it's anything more than that.

Phase vs. Group velocity

[Mendenhall]

Here comes this problem again. The article explains it, but buries it at the bottom.

What the group has attained is a transmission line with a phase velocity greater than the speed of light. This is actually not too hard to do with a resonant line (which they have), but they have constructed a cute, cheap way to demonstrate it. The group velocity, which is the speed at which information moves, is still less than c, and they explicitly say so.

The best use for a setup like this is to bring a good demonstration of the difference between the two to an undergraduate laboratory setting, to hammer into students forever the importance of the difference.

group velocities can exceed c

[alienmole]

Can't argue about New Scientist - it seems to have lost all credibility, perhaps since it began publishing on the web, I'm not sure. Luckily, we have Slashdot to correct it! ;o))

Regarding phase velocity vs. group velocity, both phase velocity and group velocity can exceed c - see Superluminal, second paragraph. Group velocities exceeding c have been done for decades - for a bit of a history, see No thing goes faster than light.

The innovation in this case seems to be that it's doable with cheap equipment, and over fairly long distances.

Even if it was possible.

[mmol_6453]

Even if it is/were possible (has anyone actually gone to the trouble to email the scientist who supposedly did the experiments?), there would be some severe expected problems.

They're talking about interfering waves. That means pulsating DC, if not straight AC. Get this up to a frequency to even be useful (ala GHz to compete with CPU or networking technology), and suddenly you're broadcasting your signal. (Though coax's construction does cause some muting of this, IIRC) And putting it on silicon is a thing for Intel to do.

And just for proof that it's not possible: "superposition."

It says that waves will pass through each other and come out the same on the other side. Easiest to see in a ripple tank, or maybe in a physlet.