A new device built by physicists to generate radiation, and named a polarization synchrotron, is really making me scratching my head. The researchers say that the intensity of the radiation generated by their synchrotron declines more slowly with increasing distance from the source than would the emission from a conventional antenna. It "is proportional to 1/r, where r is the distance from the transmitter, rather than the 1/r2 associated with spherically decaying radiation." Well, this is puzzling, but wait a minute, there is more. They also say "they can make the wave travel at greater than the speed of light (even though no physical quantity of charge travels superluminally)." In this article, PhysicsWeb reports that other physicists are skeptical. Anyway, if they are right, this could pave the way for mobile phones communicating directly with satellites without any need for relay stations.
Here is the introduction of the PhysicsWeb article.
A group of physicists in the UK and US has built a device which they claim generates radiation that circumvents the inverse square law. John Singleton of the Los Alamos National Laboratory in New Mexico and colleagues say that their table-top machine works by rotating a pattern of polarization at faster than the speed of light, and that it could be used as a new type of low-power or long-range radio transmitter. But other researchers believe that they have got their physics wrong.
The device, dubbed a polarization synchrotron by its inventors, consists of a 2 metre-long gently curving arc of alumina (a dielectric material), with a series of electrodes fitted at regular intervals along its length. Applying a sinusoidal voltage across each electrode and displacing the phase of the voltage very slightly from one electrode to the next generates a sinusoidally-varying polarization pattern that propagates along the device. By carefully adjusting the frequency of the voltage and the phase displacement the researchers say they can make the wave travel at greater than the speed of light (even though no physical quantity of charge travels superluminally).
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Here a photograph of the experimental array; the copper shields have been removed from the 41 amplifiers so that their components are visible. (Credit: see below) |
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And here is the array in use during the experiments. (Credit: see below) |
Now, let's look at this famous inverse square law.
Singleton's group believes that its polarization synchrotron, like a pulsar, emits radiation in a well-defined beam. They argue that the electromagnetic wavefronts generated by each point within the polarization pattern build up behind that point like sound waves from a supersonic aircraft. Interference between these wavefronts then reinforces the radiation along a spiral trajectory -- the beam -- that travels away from the source.
The researchers claim that the intensity of this beam is proportional to 1/r, where r is the distance from the transmitter, rather than the 1/r2 associated with spherically decaying radiation. They carried out tests on their device at the Turweston Aerodrome in Northamptonshire between May 2003 and February 2004, measuring the intensity of the emitted radiation at a range of distances up to 900 metres and mapping the three-dimensional shape of the emission.
If Singleton and his colleagues are right, what would be the utility of such a device?
According to Singleton, the polarization synchrotron could transmit radio messages with very little power or over vast distances. A scaled-down version of the device could be used in mobile phones to allow direct communication with satellites, rather than having to rely on relay stations. He says the device could also be used in radar systems, since the beam's unusual shape would make it difficult to trace the beam back to its source.
For more information, the research work will soon be published by the Journal of Applied Physics, but it's already available online. Here are two links to the abstract and the full paper (PDF format, 23 pages, 696 KB) named "Experimental demonstration of a new radiation mechanism: emission by an oscillating, accelerated, superluminal polarization current." The above images come from this paper.
If you prefer to read about this faster-than-light in vacuo phenomenon in plain english, you can check this short story, "Lawbreakers? The physics of superluminal sources."
Finally, as I don't pretend to fully understand what the researchers did, if you can add some clarification, your comments are welcome.
UPDATE (August 26, 2004): John Singleton, from the National High Magnetic Field Laboratory at Los Alamos National Laboratory sent me important information. You now can read more about "Lawbreakers? The Physics of Superluminal Sources." Here are the links to the introduction and to the full presentation (PDF format, 38 pages, 16.2 MB).
And here are Singleton's introductory comments: "The big idea is that a source travelling faster than its own waves can make several contributions to the electromagnetic radiation that turns up at a single time. In other words, emission over an extended period of the source's time frame can arrive at an instant at an observer. This is focusing in time, rather than space, and it gives rise to the 1/r decay."
Sources: Edwin Cartlidge, Physics World, for PhysicsWeb, July 29, 2004; arXiv website
2:48:27 PM
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