Posted on 09/16/2002 7:26:53 AM PDT by aculeus
Electric signals can be transmitted at least four times faster than the speed of light using only basic equipment that would be found in virtually any college science department.
Scientists have sent light signals at faster-than-light speeds over the distances of a few metres for the last two decades - but only with the aid of complicated, expensive equipment. 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.
Jeremy Munday and Bill Robertson made a 120-metre-long cable by alternating six- to eight-metre-long lengths of two different kinds of coaxial cable, each with a different electrical resistance. They hooked this hybrid cable up to two signal generators, one of which broadcast a fast wave, the other a slow one. The waves interfere with each other to produce electric pulses, which can be watched using an oscilloscope.
Any pulse, whether electrical, light or sound, can be imagined as a group of tiny intermingled waves. The energy of this "group pulse" rises and falls over space, with a peak in the middle. The different electrical resistances in the hybrid cable cause the waves in the pulse's rear to reflect off each other, accelerating the pulse's peak forward.
Four billion km/h
By using the oscilloscope to trace the pulse's strength and speed, the researchers confirmed they sent the signal's peak tunnelling through the cable at more than four billion kilometres per hour.
"It really is basement science," Robertson said. The apparatus is so simple that Robertson once assembled the setup from scratch in 40 minutes.
While the peak moves faster than light speed, the total energy of the pulse does not. This means Einstein's relativity is preserved, so do not expect super-fast starships or time machines anytime soon.
Signals also get weaker and more distorted the faster they go, so in theory no useful information can get transmitted at faster-than-light speeds, though Robertson hopes his students and others can now rigorously and cheaply test those ideas.
Physicist Alain Hache at the University of Moncton in Canada adds that 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.
© Copyright Reed Business Information Ltd.
There have been three or four spates of articles over the past few years in the popular press about FTL signals, but this is the first time I recall the difference between group velocity and phase velocity being mentioned in the article itself, so I count that as progress. Let me see if I can illustrate it more clearly.
Suppose I have a train that's four miles long. It passes through Hicksville on the way to Podunk, which is four miles away. It is travelling at thirty miles per hour, which is the speed limit on the line. Any faster, and the conductor gets reprimanded.
Officially, the location of the train is counted as the center of the train, no matter how long the train is. By the time the train officially leaves Hicksville, the train's engine is halfway to Podunk. At that point, unbeknownst to the engineer, who is preoccupied with the train's speedometer, the engine and the first few cars of the train get decoupled from the rest of the train. Four minutes later, the train--now consisting of the engine and a few cars--arrives at Podunk.
The official speed of the train is 60 miles per hour, which is twice the speed limit. The engineer is duly reprimanded, and customers line up to buy tickets for the new high-speed rail service.
You mean the ones that teach the difference between phase and group velocity?
I do that all the time, and it just glows slightly. Quite pleasant, really. Should I worry?
First, we have a living cat and place it in a thick lead box. At this stage, there is no question that the cat is alive. We then throw in a vial of cyanide and seal the box. We do not know if the cat is alive or if it has broken the cyanide capsule and died. Since we do not know, the cat is both dead and alive, according to quantum law, in a superposition of states. It is only when we break open the box and learn the condition of the cat that the superposition is lost, and the cat becomes one or the other (dead or alive).
We know that superposition actually occurs at the subatomic level, because there are observable effects of interference, in which a single particle is demonstrated to be in multiple locations simultaneously. What that fact implies about the nature of reality on the observable level (cats, for example, as opposed to electrons) is one of the stickiest areas of quantum physics. Schrodinger himself said, later in life, that he wished he had never met that cat.
That's a good one.
Now how about this part? How does an oscilloscope trace (operating far, far below the speed of light) measure (or confirm a meaurement of) anything at, or above, the speed of light without combining measurements of multiple pulses or simply tracking some phase shift of the combination signal? It still seems to be very sloppy writing and/or very sloppy lab work to me.
Electrons travel MUCH slower than 2/3s light speed in wires. In fact, it is actually ELECTRIC FIELD that produces what we know as electromotive force, electromagetic waves, and various other phenomenon...
Electrons actually "drift" through a conductor at VERY slow speeds. Accordingly, this phenomenon is known as Electron Drift.
Given a copper conductor with a diameter of 2mm, and a DC current of 1 Amp, it would take 12 hours for an electron to travel 1 meter..
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