Talk:Neutrino telecommunications

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[edit] For those interested

This stuff really isn't my cup of tea, but it is interesting still. In case someone would like to add soem stuff, and the link for some reason should no longer work, here is the whole article (I am aware of copyright problems, but since the information is sourced and quoted, and this is not the actual wikipedia article but a discussion about it, maybe it is OK if I post it here if someone wants to use its content as an inspiration to add further details to the main article. If it is not OK, just delete all or most of it.):

"From tires to neutrinos New Scientist vol 182 issue 2443 - 17 April 2004, page 36 Who needs cables or satellites when you can send a message through the Earth on a beam of neutrinos? Matin Durrani explains Pirelli's wackiest project

IN A windowless laboratory in Milan, Luca Gamberale and Flavio Fontana admire a handful of sapphires. The crystals are part of an experiment designed to detect neutrinos, ghostly subatomic particles that stream from the sun in their countless trillions every second. But Gamberale and Fontana do not work for a university or government research lab - they work for Pirelli. So why is a company famous for its tyres and glamour calendars interested in neutrinos?

Gamberale and Fontana are not too concerned with the properties of these enigmatic particles. They're simply trying to repeat an experiment carried out 20 years ago by researchers at the University of Maryland. That experiment suggested that neutrinos could form the basis of a novel communication system that would allow messages to be transmitted to the other side of the world without wires, cables or satellites.

Many physicists find it hard to believe that neutrinos could be harnessed for this purpose, because they are so tricky to spot. But if they could be tamed, neutrino telecommunications would do away with the costly and time-consuming business of launching and maintaining satellites, or building and laying thousands of kilometres of fibre-optic cables on the seabed. Pirelli is interested because it doesn't just make tyres, it is also a world leader in fibre optics. It believes neutrino research could reap long-term rewards.

"The project belongs to what we call blue-sky research," admits Fontana, who is head of Pirelli's materials innovation group. "The topic is extremely controversial, but if it is successful the company will have a big technological breakthrough on its hands."

It's not difficult to see why Pirelli's research is raising so many eyebrows. Neutrinos are fiendishly difficult to detect because they interact so weakly with matter. Several trillion will have passed through your finger in the past second alone, without you noticing a thing.

You can increase the odds of spotting a few neutrinos by building a giant detector. The Super-Kamiokande experiment in Japan, for instance, consists of 50,000 tonnes of ultra-pure water housed in a giant underground cavern. On the rare occasions when a neutrino hits a nucleus in the water, it changes into a charged particle, which then goes on to produce a flash of light.

But even before an accident three years ago destroyed much of the detector, Super-Kamiokande was spotting only a small fraction of the neutrinos that passed through it. It's hard to imagine how a diminutive sapphire crystal could do any better.

Fontana first got wind of the idea in the mid-1990s from Giuliano Preparata, a theoretical physicist at the University of Milan. A few years earlier, Preparata had worked on an idea dreamed up by University of Maryland physicist Joseph Weber, who was regarded by many as a maverick experimentalist.

Weber once claimed to have detected gravitational waves, ripples in space-time whose existence is predicted by Einstein's general theory of relativity. But no one quite believed him. And as he neared retirement in the 1980s, funding for his gravitational wave detector was slowly diverted to other groups. Desperate to continue employing the technician and computer programmer who had kept his equipment running for over 30 years, Weber asked a colleague for advice.

The colleague recommended Weber turn his experience in looking for gravitational waves to the hunt for the elusive neutrino. Never one to ignore a serious scientific challenge, especially when it came from Caltech physicist Richard Feynman, Weber immediately began scribbling formulae and drawings. He calculated that certain ultra-stiff crystals would detect neutrinos far more effectively than most other materials. Conversely, it might even be possible to generate an intense beam of neutrinos from one of these crystals - a neutrino laser.

Neutrinos calling Slowly it dawned on Weber that neutrinos could form the basis of a novel telecommunications system. If you took a neutrino laser and fired a beam towards a receiver on the other side of the planet, the neutrinos would pass straight through the Earth at almost the speed of light and reach it unhindered, without spreading out. Armed with a neutrino-detecting crystal at the other end, the recipient could pick up the signal and read it. The delicate fibre-optic cables that telecoms firms use to send signals encoded in light pulses around the world would be unnecessary. And unlike light, which spreads out and eventually gets absorbed in the glass fibres, there would be no need to keep the beam focused or install costly amplifiers to boost the signal along the way.

Weber also reckoned that these special crystals could generate a neutrino beam a few centimetres wide and with the same energy as a 20-watt light bulb. Because neutrinos interact with normal matter so infrequently, such a beam would lose barely a few million billionths of its power as it journeyed through the Earth. At least that was the idea. As a first step, Weber decided to try building a super- sensitive neutrino detector. To fund his research he approached the US Department of Defense and explained to officials that a working device could be used to detect the neutrinos emitted by nuclear reactors, such as those powering Soviet submarines. With the cold war still in full swing, they decided his research was worth a try.

Weber set to work. But when he claimed limited success at detecting neutrinos, no one quite believed him. Then the cold war ended and his funding dried up. Weber retired in 1989 and even though he continued his research in private, neutrino communications seemed a lost cause. When Weber died in September 2000, the dream appeared to be over.

Weber's big idea was that pure crystals with extremely strong bonds connecting their nuclei make much better neutrino detectors than other materials with weaker bonds. According to conventional thinking, the ability of a material to detect neutrinos should increase in direct proportion to the total number of nuclei that it contains. But Weber's theoretical calculations showed that in an ultra-stiff crystal, the signal strength, or number of neutrinos detected, would rise with the square of the number of nuclei.

If he was right, it would make spotting neutrinos quite a bit easier. A sapphire crystal a few centimetres across contains approximately a hundred billion billion atoms. So its ability to detect neutrinos bouncing off its nuclei should be a hundred billion billion times higher than from a conventional material with the same number of nuclei.

The reason for this odd behaviour lies in how nuclei oscillate. When a neutrino hits a nucleus it is temporarily absorbed, with the nucleus gaining energy in the process. The nucleus then spits out the neutrino and loses energy, recoiling as it does so. In materials with weak atomic bonds, all the nuclei oscillate out of synch and the recoil momentum is very small. When Weber looked at the equations describing this "incoherent" process, he found that because of this infinitesimal recoil momentum the neutrino is unlikely to be knocked off its original course.

However, in a rigid crystal, where the nuclei are tightly linked to each other, Weber's equations showed that when a neutrino struck one of the nuclei, its energy would be quickly transferred to the rest of the crystal, as if all the nuclei were connected together by stiff springs. Because the nuclei would act in harmony, he reckoned their combined recoil momentum would be much more likely to throw a neutrino off course than a single nucleus, and the crystal would scatter neutrinos in a "coherent" manner. But he didn't know that the nuclei would oscillate in harmony - he simply assumed this when he derived his equations. Possible confirmation came in the mid-1990s when Preparata claimed to have found theoretical evidence. He calculated that certain materials such as sapphire, under certain conditions, contain myriad regions or "domains" about 1 micrometre across made up entirely of atoms that oscillate in unison. These form because they stabilise the crystal.

To test his theory, Weber suspended a horizontal aluminium disc from a support by a thin tungsten wire. He then attached two identical crystals of sapphire at diametrically opposite sides of the disc. Facing one of the crystals was a steel capsule containing titanium tritide, a radioactive material that emits streams of antineutrinos, subatomic particles which have virtually identical properties to neutrinos. The other crystal sat next to a capsule that contained no titanium tritide and so emitted no antineutrinos. If Weber's theory was correct, antineutrinos emitted by the titanium tritide should strike some of the nuclei in the sapphire, giving it a small nudge that would make the disc twist. By measuring the force needed to return the disc to its starting position, Weber would be able to calculate the strength of the nudge. After months of careful experiments, he concluded that the sapphire was indeed acting as a detector.

To double-check that minuscule differences in the gravitational pull of the capsules on the disc were not affecting the results, Weber modified the apparatus to study the effect of antineutrinos streaming from a nuclear reactor 15 metres away and found the same effect. He even claimed to have detected neutrinos from the sun. Since both sources were so far away, he could rule out the effects of gravity.

Weber wanted to wait until the project was completed before going public with his results. But he soon came under pressure from the military, receiving an ultimatum to submit the work for publication. Reluctantly, he sent it to Physical Review C, the most conservative journal he knew. The journal was quick to accept and publish Weber's work (vol 31, p 1468).

Risky business The paper immediately drew stinging criticism. If neutrinos can scatter coherently from sapphire, physicists argued, why is this effect not seen when neutrons or X-rays strike such a crystal? Others pointed to mathematical errors in Weber's calculations. One team at Johns Hopkins University in Baltimore, Maryland, led by James Franson and Bryan Jacobs, tried to see for themselves if solar neutrinos would interact with sapphire crystals in the way that Weber predicted. They failed. But that has not deterred Fontana from resurrecting the idea after long discussions with Preparata. "We were fascinated by Weber's work," recalls Fontana, who decided to spend some of the money Pirelli sets aside for bold and risky concepts to try repeating Weber's experiments.

Four years ago he recruited Gamberale, a former PhD student of Preparata, to lead the research project. He also rescued Weber's old lab equipment and brought it back to Pirelli's research labs in Milan.

The company now has an experiment on the go designed to measure neutrinos from the sun using a tuning fork (see Graphic). A small crystal of pure silicon, another ultra-stiff material, sits at the tip of one prong, while an aluminium crystal with the same mass sits at the end of the other. Facing the fork is a heavy aluminium ring containing a set of six sapphire crystals arranged around the circumference. The ring rotates so that, at regular intervals, the sun, one of the sapphires and the silicon crystal are all exactly in line. When this happens, the sapphire should scatter some of the solar neutrinos and lower the number striking the silicon. But when any of the sapphire crystals is not in line, the intensity of neutrinos hitting the silicon should rise.

As the aluminium ring rotates, the sapphire crystals move in and out of the line of sight, which should lead to a steady rise and fall in the number of neutrinos striking the silicon, giving it a regular series of kicks. By making the ring rotate at exactly one sixth of the resonant frequency of the tuning fork, the kicks can be exactly timed to make the fork vibrate. Even though the oscillations would be minuscule, they are still big enough to be picked up by piezoelectric crystals attached to the fork.

The experiment is far from easy and so far Gamberale has been unable to get any definite results with neutrinos. He is still calibrating his equipment with an optical laser and is trying to eliminate extraneous vibrations and other background noise. What's more, he has to work out the precise alignment of his equipment relative to the sun, though he has had the help of a theodolite donated by the Italian military.

Of course, even if Gamberale does eventually detect neutrinos, his equipment is a long way from a full-blown telecommunications system. He warns people not to expect too much too soon. "We are not very close to using such technology," he says. "At present we have no signal from neutrinos and only a small signal from light." Yet Gamberale is encouraged by the results so far with a laser because they hint that coherence plays a role in determining whether scattering occurs. His calculations show that if the results are true for light, they should also be true for neutrinos.

But if Pirelli is ever going to get a working neutrino telecommunications system off the ground, the company needs a device to generate neutrinos. Weber originally thought that you could create such a device by reversing the mechanism for detecting them. And he was even granted a US patent for the idea. If a neutrino striking a crystal can make it vibrate, he reasoned, then surely it must be possible to generate neutrinos by making the crystal vibrate. You would also need a way of varying the intensity of the neutrino beam so that a message could be encoded in the signal.

Maury Goodman, a particle physicist from the Argonne National Laboratory in Illinois, is sceptical about the entire idea. "The challenges are so large that I cannot think what the advantages might be," he says. "Neutrino beams are not steerable so any intended recipient would have to be in a fixed place for a long time. If they knew they had to do that, you could probably tell them whatever you were going to say by some other way."

Fontana is more bullish - he thinks the technology could become viable in about 10 years' time. "We know that there is a huge ocean of experimental difficulties to overcome before having something that could work," he says. But he points out that calculations by theorists Allan Widom from Northeastern University in Boston and Yogi Srivastava from the University of Perugia in Italy, confirm that stiff crystals should be able to detect neutrinos.

Fontana thinks that by the end of the year his group will have proved that it is possible to detect neutrinos with sapphire crystals. But even the most positive findings are unlikely to see messages encoded on neutrino beams criss-crossing the Earth anytime soon, especially as Pirelli is setting aside a mere $150,000 a year for neutrino research. If you were thinking of investing in sapphires in the hope of cashing in on a new telecoms boom, you might want to stick to jewellery." Rhynchosaur 11:18, 23 October 2006 (UTC)