Electrical pulses break light speed record

Physics WEB ^ | 22 January 2002 | (A Haché and L Poirier 2002 Appl. Phys. Lett. 80 518).

[vannrox]

Electrical pulses break light speed record
22 January 2002


Pulses that travel faster than light have been sent over a significant distance for the first time. Alain Haché and Louis Poirier of the University of Moncton in Canada transmitted the pulses through a 120-metre cable made from a coaxial 'photonic crystal'. The achievement raises hopes that data could travel through electronic communications systems at almost the speed of light (A Haché and L Poirier 2002 Appl. Phys. Lett. 80 518).


When a pulse of radiation travels through a 'dispersive' medium, different wavelengths in the pulse move at different speeds and the pulse becomes distorted. Ordinary dispersion arises when the refractive index of a material changes with increasing wavelength. This stretches out the pulse and reduces the group velocity - the speed at which the peak of the pulse travels.


But 'anomalous dispersion' can occur in materials that absorb radiation in a certain range of wavelengths. The refractive index on either side of this absorption band changes sharply with wavelength. In these regions, the components of radiation at the tail of the pulse interfere destructively, and the peak of the wave is effectively pushed forward.


To create their cable, the Canadian researchers joined together five-metre sections of coaxial cable with alternating electrical impedences. Radiation in the frequency range 9 - 11 MHz is partially reflected at the boundaries of these segments, which gives the cable its absorption band. Haché and Poirier sent electromagnetic pulses with frequencies between 5 and 15 MHz through the cable, and found that the group velocity reached three times the speed of light for frequencies in the absorption band.


Haché and Poirier emphasize that their experiment does not break any laws of physics. Although the group velocity exceeds the speed of light - an effect permitted by relativity - each component of the pulse travels slower than light. It would be impossible to transmit information faster than light because it would be encoded onto a single frequency component.


But as Haché explains, many existing information systems are based on coaxial cables, and the current top speed for data is just two-thirds the speed of light. If the impedance of such cables were adapted, pulses sent at frequencies close to the absorption band could transmit information at speeds approaching that of light.


'Oddly, the reason no one has done this before is that we are using what most people are trying to avoid - the back-reflection caused by impedance mismatch', Haché told PhysicsWeb. 'But as far as superluminal propagation goes, this is the key'.

[vannrox]

ERP...

[Bigg Red]

BTT

[MosesKnows]

coaxial cable with alternating electrical impedences

I am not sure I understand what is meant by "alternating electrical impedences". However, if it means that the impedances were purposely mismatched at each section of cable I have a grasp of the information offered.

[VRWC_minion]

Is the following sexually suggestive or is it just me?

When a pulse of radiation travels through a 'dispersive' medium, different wavelengths in the pulse move at different speeds and the pulse becomes distorted

[RightWhale]

Well, did they or didn't they? Some kind of pulse travelled at 3xC, but data still can't travel at quite C. Sounds like the story hasn't changed. I remember an article in a ham magazine back in the late 50s describing a wire loop where a pulse could be made to travel at speeds above C. What was the author's name? Green, I think.

[stylin19a]

Ok, I get it:
Nothing Goes Faster Than Light

[PeoplesRepublicOfWashington]

I hope you know a good therapist.

[smokinleroy]

Nothing Goes Faster Than Light

It might if they powered it from a perpetual motion machine!

SL

[vannrox]

"...To create their cable, the Canadian researchers joined together five-metre sections of coaxial cable with alternating electrical impedences. Radiation in the frequency range 9 - 11 MHz is partially reflected at the boundaries of these segments, which gives the cable its absorption band. Haché and Poirier sent electromagnetic pulses with frequencies between 5 and 15 MHz through the cable, and found that the group velocity reached three times the speed of light for frequencies in the absorption band..."


So from what I understand this is only applicable in the 9 to 11 MHz range and is void at lower frequencies than 9MHZ and higher than 11 MHZ. But that is only in respect to the given test. It would be rather hasty to conclude that it is unique to the absorbption band of the physical cable. That is what is being implied by this article. If you take this as it is implied then...


Use of the cable in a advanced computer would enable faster operation that one that utilizes a CPU at frequencies of 1GHz. I find that exclusionary.

[Poohbah]

Some kind of pulse travelled at 3xC

3xC in a 1xC zone. Boy, yo's in a HEAPA trouble!

186,000 miles per second: it's not just a good idea, IT'S THE LAW!

[pabianice]

They obviously used a trans-warp conduit.

[dead]

If they're going to build faster than light communications, why hasn't the me of tomorrow contacted the me of today and let me know what companies to invest in?

Future me must be a lazy ass.

[skateman]

They obviously used a trans-warp conduit.

Not only that, but it was the Vulcans that gave them the idea.

[VeritatisSplendor]

A pulse travelling faster than the data. Is that like if I had a really bright flashlight, and swept the beam across an arc of sky from Mercury to the moon in a second, say 95 million miles or 500 light-seconds?

The spot of light travels at 500 c or any speed you like, and yet any data from Mercury to the moon takes 500 seconds to arrive.

Mrs VS

[Aurelius]

BUMP

[RightWhale]

Yes, that is one way to look at it. Interference patterns are used to aim radar beams and they can switch instantly from one look angle to another. The pulse propagation is very similar. It looks superficially like a wavefront, but isn't carrying any information.