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

i wholehearteddly believe this

[krog]

anyone selling a bridge?

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

[orac2]

One second is defined as "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom."

The meter is then defined in terms of this. There really are very few basic, basic units, and the kilogram is currently the only one which still relies on an actual physical prototype, and NIST are currently working on a 'electric' kilogram.

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!

I did this years ago

[briglass]

Using onion skins, sixty-four removed coke labels and an ampersand.

Re:I did this years ago

[laserjet]

In my day, we didn't have ampersands. We had to print out the letter S, cut it out, paste it upside-down, and draw a line through it to speed up those damn atoms. And even then, it only worked on Tuesdays. You have it lucky, I'll tell you.

Confusing headline

[Bonker]

Speed Of Light Broken With Off Shelf Components

Careful here, guys. Breaking the speed of light would be a truly wondrous, nobel-prize winning acheivment. Building transmission eqipment which boosts signal speed is really good and worthwhile, but nowhere near as important an advanced as superluminal transmission.

Please check your headlines!

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.

Isn't this like the moving beam of light?

[ocie]

Imagine a rotating laser light source. If you had a laser beam that was rotating at only 2rpm, the beam would move across the surface of the moon at approx 1.7 times the speed of light, but you are not really moving anything (not even light) at more than c. You can't use this to transmit any information or power.

GAH

[gclef]

Ye gods, I hate these types of stories. The real physics is always more subtle and interesting than the press makes them out to be.

The vast majority of the experiments I've seen like this (I've really only looked at photon tunneling, but this sounds *very* similar from the write-up) are explained by wave-shaping, and the side-effects of that, and are not actually FTL at all. But of course, that's hard to explain to people, so the New Scientist, et al, just go for the "Speed of light broken!" headline, which mis-leads everyone.

Grrr.

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.

Related Stories

[RedWolves2]

Did you see the related stories associated with this article?

Related Stories

Black hole theory suggests light is slowing
8 August 2002

Light may have speeded up
15 August 2001

So which is it light is speeding up or slowing down???

Re:A guy in Arizona bought the London bridge....

[perlyking]

Not quite.. the thing is not that it was falling down but that the guy thought he was buying Tower Bridge.

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

a better analogy

[lommer]

I think the best analogy I've ever seen is the one using ping pong balls.

Imagine you have a long tube filled with pingpong balls all the way to each end. Then, when you push another ball in one end, what happens? Another ball immediately pops out the other end, at exactly the same speed that you pushed in the first one, but potentially miles away from your end of the tube. But still, none of the pingpong balls ever went faster than you pushed in the first one.

Re:a better analogy

[Fortuna Wolf]

Except that this analogy is wrong.
In some cases electrical signals work like that, but don't travel instantaneously.
No object is totally rigid, its forbidden somewhere in the laws of physics. The balls will compress slightly and then a wave either in the movement of the balls or their getting compressesed and then expanding. Its akin to taking a stiff object and swinging it, if you swing it fast enough and its long enough, the end won't break the speed of light because its not completely rigid.

Re:a better analogy

[kalidasa]

wait, say I have a string 1AU long, and I swing it with a peroid of 6 seconds, why would the end not be going faster than light?

Figure out the mass of it . . . it will take a hell of a lot of energy to whip a string 1 AU long. Eventually you'll start running into relativistic effects at both ends of the string; dilation of both time and length, massive increases of the string's mass (remember, when an object gets up to relativistic speeds its mass dilates upward, and more force is required to accelerate it at the same G; the mass of the tip of the string will approach infinity as its velocity approaches c).

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.