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

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!

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.

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 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.