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

186,000 miles per second

[sulli]

it's not just a good idea, it's the law!

Re:186,000 miles per second

[netsharc]

Define "one second". :)

The time taken for light to travel 1 / 299792458 metre?

Re:186,000 miles per second

[Dirtside]

it's not just a good idea, it's the law!*

Actual mileage may vary.

First Post at Light Speed!

[Anonymous Coward]

Ack! I bet by the time I hit submit, some other guy using electrons travelling faster than light will have beaten me to first post!

Damn you technology!

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.

This article is so bad it's not funny.

[rsidd]

The "peak of the signal" (ie, the phase velocity) can travel faster than light -- big deal. It's been known for a long time. The "group velocity", as the article points out, is not faster than light, so no energy is being transferred faster than light, so relativity isn't being violated.

If you want to see a "thing" travelling faster than light, sweep a searchlight across a cloudy sky. That lit-up patch can, in principle, travel faster than light -- but it's not matter or energy, only an appearance.

And the last paragraph: "electrons usually travel at two thirds the speed of light". Wow, who needs particle accelerators?

What is a writer who can't distinguish the speed of electrons from the speed of the electrical signal doing writing for New Scientist? What is New Scientist doing publishing such crap?

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.

sensible weights and measures

[spongman]

c ~ 1802617528320.3 furlongs/fortnight

Ludicrous speed!

[McFly69]

Sandurz: Prepare for light speed.
Helmet: No, no, light speed is too slow.
Sandurz: Light speed too slow?
Helmet: Yes, we'll have to go right to...Ludicrous speed!
Sandurz:Ludicrous speed! Sir, we've never gone that fast before. I
don't think the ship can take it.
Helmet: What's the matter, Colonel Sandurz...CHICKEN?!

New slashdot tagline

[ucblockhead]

"Slashdot! We don't suck any worse than the traditional media!"

Phase Velocity vs. Group Velocity

[Effugas]

I'm going to munge this pretty righteously, but it's for a good cause (explaining how the speed of light wasn't violated).

Take a bunch of cars in traffic -- stop 'em, say there's an accident. Cops go ahead, clear the accident. Open road, right? Clear to go 65.

Does the entire traffic jam disappear immediately? Nope. Each *car* may be able to go 65 now, but they have to wait for the car in front of them to go away. That takes time -- two to five seconds. There's a bit of a blurring, as people see cars three or four cars ahead start to speed up -- but just because the cars *could* go sixty five, doesn't mean they *are*.

If you were sitting above the traffic in a copter, you'd look down and see a "pulse" travel slowly back through the crowd, as slowly everyone saw the car in front speed up. Eventually the entire group would speed up to some maximum speed.

The speed of the cars forward is the group velocity (more or less).

The speed that "all clear" pulse went backwards, that's the phase velocity.

Imagine everyone was drunk -- that pulse would go back really, really slow. Imagine everybody's car had a computer, linking 'em together. The *moment* the guy in front of them moved, they'd speed up too. That pulse would go quite fast, and traffic would be rather more bearable.

Same speed limit -- same group velocity -- but phase velocity ranges from near zero to past the speed of light, depending on whether drunk drivers or synchronized computers are behind the wheel.

At no point does any care break the speed of light, though :-)

--Dan

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.