How to get a bigger bang from your accelerator 12 May 01
MACHINES that can boost particles to the huge energies needed to reveal supersymmetry may be easier to build than physicists thought.
Teams in the US, Europe and Japan are all working on rival designs for the next big linear accelerator, in which beams are accelerated from either end and collide in the middle (New Scientist, 31 March, p 6). Till now, physicists believed they would need a machine up to 25 kilometres long to get particles to such high energies, but Pantaleo Raimondi and Andrei Seryi of the Stanford Linear Accelerator Center in California believe they can shrink it.
The reason you need such large machines is because particles travelling at slightly different speeds are bent differently by focusing magnets, an effect called chromatic aberration. Designers usually deal with this by adding two hexagonal magnetic fields called sextapoles-one for vertical deflection and one for horizontal-that reverse the effect of the focus magnets. But they have to position the sextapoles several hundred metres from the focus magnets and each other to avoid another uncontrollable aberration.
However, Raimondi and Seryi found a way to put two sextapoles close to the beam focus, one designed to remove vertical chromatic aberration, the other designed to remove the second effect. "We're able to design a shorter system by tuning all these different knobs," says Seryi. The design should reach energies of 3 to 4 teraelectronvolts, far above the 0.5 TeV currently planned.
From New Scientist magazine, vol 170 issue 2290, 12/05/2001, page 18
If you want to know the time, ask a bubble 05 May 01
A CLOCK made of bubbles is the brainchild of Fred Romberg of the California Institute of Technology. Romberg got the idea after watching the bubbles in a glass of soda. "I thought that if I could control the motion of the bubbles, I could start making letters, numbers and other shapes with them."
Romberg has now built a prototype clock to demonstrate the idea. Two sheets of glass make the front and back of a thin tank filled with baby oil. A row of tiny valves along the bottom releases bubbles of dye into the oil. Because the dye is less dense than baby oil and doesn't mix with it, the bubbles rise slowly to the top of the tank, where the dye can be collected and recycled.
By opening the valves in a sequence carefully determined by a microchip, Romberg is able to produce formations of bubbles that show a clock face in either digital or analogue form. The display rises to the top of the tank and then the next set of bubbles is released.
"It's a gimmick," says Peter Church, a manager at the Technology Innovation Centre at the University of Central England in Birmingham. "But I'm sure motor cars seemed a gimmick once."
From New Scientist magazine, vol 170 issue 2289, 05/05/2001, page 19
Warp speed 28 Apr 01
If your dad told you how to go faster than light, would you build a machine to do it? Nick Appleyard and Bridget Appleby investigate
THE SPEED of light can't be exceeded. Everyone knows that. Yet Houshang Ardavan of Cambridge University claims that there are sources of radio waves out in space that move faster than light. A team of physicists at Oxford, including Ardavan's son, has built a "superluminal" source based on Ardavan's ideas. And any day now it could be switched on.
Many physicists think this idea is a complete waste of time. But if they're wrong, and the Oxford experiment succeeds, Ardavan's patented superluminal transmitters could soon turn up in your pocket. Their weird radiation could transform technologies from medical scanners to mobile phones.
Ardavan's work was inspired by the mysterious celestial objects known as pulsars. Pulsars send out pulses of radio waves several times a second, with timing so regular that they were at first thought to be alien transmissions. Astronomers now believe that pulsars are the remnants of massive stars that ended their lives in enormous supernova explosions. Each supernova is thought to have left behind a ball of neutrons 1.4 times the mass of our Sun but only 20 kilometres across, its material so dense that a teaspoonful would weigh three billion tonnes.
Although most astronomers agree on the basic nature of pulsars, the radio pulses remain a bugbear. "More than 30 years after the discovery of pulsars, we still don't know how the radio waves are produced," says Janusz Gil of the J. Kepler Astronomical Center in Zielona GÓra, Poland. "Explaining pulsar radiation is one of the most difficult problems of astrophysics." The regularity is thought to come from the fact that pulsars spin, typically 10 to 20 times a second. Somehow they must send out a beam of radio waves that sweeps past the Earth on each rotation.
But how? Most theories depend on the intense electric and magnetic fields that are thought to surround a pulsar. The magnetic field can be a hundred billion times the Earth's field - strong enough to wrench a spanner out of your hand from across the Atlantic. The general idea is that the fields accelerate electrons near the pulsar, causing them to emit radio waves. But to produce the required radio intensity, these theories have to include some awkward assumptions (see "Tackling the pulse").
Ardavan's theory is radically different. He says that the pulses we see are "light booms"-shock waves made by a source moving faster than light, rather like the sonic boom created by a supersonic plane when it breaks the sound barrier. The idea of a light boom is not new. Because light slows down inside materials such as water or glass, particles moving in such a medium can travel at speeds faster than sluggish light. These particles emit a flash of blue light called Cerenkov radiation.
Ardavan proposes that light booms could occur even in a vacuum, where light travels at top speed. How can this be? According to Einstein's theory of relativity, no material particle can move faster than light in a vacuum.
But a pattern can. For example, if a long line of drummers each hits a drum in turn, the pattern of drumming can easily exceed light speed. Of course, real drummers would have to be pretty skilled to hit their drum each at the precise prearranged time.
Ardavan points out that faster-than-light patterns could be circling around pulsars. A pulsar's magnetic field rotates along with the star. As it does so, it induces a rotating pattern of electrical charges and currents in the surrounding gas. This pattern rotates as if rigid, so the farther out you go from the pulsar, the faster it sweeps by-just as the spot illuminated by a lighthouse moves faster further out at sea. Beyond about 5000 kilometres from the pulsar, the pattern will be circling faster than the speed of light.
Vitaly Ginzburg and his co-workers at the Lebedev Physical Institute in Moscow were the first to examine radiation from faster-than-light patterns of charge. They predicted the existence of light booms, but they didn't work out what would happen if the source moved on a curved path-a question that requires fiendishly complicated maths. Ardavan realised that much of the mathematics he needed had already been worked out for supersonic systems, so he started by working on the theory of supersonic helicopter blades, which mimic the whirling magnetic patterns around pulsars.
Adapting this work to his pulsar model, he calculated in 1994 that such a rotating pattern would produce a shock wave of light. As each patch of charge loops around, the waves it emits pile up in a complicated fashion, crowding together especially strongly in a "cusp" of radiation that follows a spiral path (see Diagram).
Using pulsars to go faster than the speed of light
To explain the whirling beam that flashes radio waves at Earth, Ardavan presumes that the overall charge pattern around a pulsar must be lopsided. Perhaps a few closely clustered regions in the pattern act as especially intense sources, and their cusps of radiation combine into the radio beam.
This radiation has one strange unforeseen property. Radiation from any ordinary source, be it lightbulbs or laser beams, spreads out and fades rapidly as it travels. The intensity falls in proportion to the square of the distance from the source. But in 1998, Ardavan published a paper showing that radiation from a superluminal source should fade only in proportion to the distance ( Physical Review E, vol 58, p 6659). The reason for this slower decay is that further from the source, the set of waves forming the cusp overlap and get squashed together into a tighter beam, so the intensity will no longer drop off as quickly.
Ardavan's ideas aren't popular, however. Among those who disagree violently is Tony Hewish of Cambridge University-one of the original discoverers of pulsars. The entire concept is wrong, he says. "Frankly, I think the error is in equation one." He doesn't believe that a collection of particles all moving slower than light can produce superluminal shock waves, even if the charge pattern moves faster than light. Hewish also points out that many common types of antenna and waveguide already carry superluminal charge patterns, yet this slower decay in brightness has never been seen.
Ardavan accepts this, but says an antenna would have to be curved to emit his slow-decay waves. The charge patterns not only have to be moving faster than light, they must be accelerating. Speeding up, slowing down or moving around in a circle would do, but steady motion will not produce the vital cusp.
Ardavan claims that there is already evidence to support his theory. In 1999, Shauna Sallmen and co-workers from the University of California at Berkeley used a high-resolution technique to examine the pulsar at the heart of the Crab Nebula. Instead of a single source, they saw three separate points-a characteristic of superluminal sources. As Jean-Luc Picard of the USS Enterprise has demonstrated, a starship that exceeds the speed of light can overtake its own image and appear to be in more than one place at a time. So the Crab pulsar seems to be performing the Picard manoeuvre, appearing in three places at once. Ardavan was overjoyed.
Despite this, pulsar researchers have not embraced Ardavan's model. He believes that this lack of acceptance might partly be due to a poor understanding of the superluminal regime of electrodynamics, which he says has taken him 20 years to comprehend. "Many of the unfamiliar superluminal effects are at first sight counter-intuitive," he says. Another problem is the formidable mathematics. To do his integrals Ardavan uses an obscure technique that almost nobody else understands. As pulsar theorist Don Melrose of the University of Sydney says: "The combination of an unconventional idea and an unconventional approach makes us all uncomfortable."
Melrose is sympathetic to the theory, but doesn't believe it actually applies to pulsars. The rotating charge patterns, he thinks, would be unstable. Other pulsar theorists object that Ardavan's theory doesn't explain every detail of the observations.
This debate might have dragged on for decades, but two years ago a way to test the theory appeared. Ardavan's son, Arzhang, became interested in the problem after completing a doctorate in experimental physics at Oxford. "My father's theory was dinner table conversation for a long time," he says. He joined forces with John Singleton of the Clarendon Laboratory, and together they now have £330,000 of research council funding to build a table-top pulsar. The money had been earmarked for developing "non-derivative" instruments-those based on original principles. "This is wildly non-derivative," says Arzhang Ardavan with a smile.
The core of their device is a curved rod of aluminium oxide covered with electrodes. The voltage on each electrode will be oscillated at radio frequency, with a slight time delay from one electrode to the next. The idea is that this will mimic the line of drummers, to create a pattern of waves that moves along the rod faster than light.
The hardware of their "polarisation synchrotron" is all in place, so now Singleton and Arzhang Ardavan just have to get the delicate timing of the electrodes right.
If it works, the weird radiation produced will be tremendously useful. The device could be tuned to emit radiation over a very wide range of the electromagnetic spectrum, including previously inaccessible terahertz radiation.
Terahertz waves penetrate the skin, but cause less tissue damage than X-rays, so they could be used to diagnose skin and breast cancers, as well as rotten teeth, with little health risk. Mobile phones using terahertz waves would have access to a bandwidth thousands of times greater than today's, making data-hungry applications like video streaming a breeze. And a terahertz source could also be used as a computer clock, allowing elements to switch far faster than in today's PCs.
Houshang Ardavan predicts that the radiation from this table-top pulsar will fade more slowly than that from any other source. This would be very useful for long-distance communications: space probes could send information back to Earth using small, low-power superluminal transmitters. Mobile phones could beam directly to a satellite without needing a ground-based relay station, so you could use them anywhere on Earth. Strangest of all would be a new means of transmitting secure communications. With the right antenna, you could send out a pulse that only assembles itself in one place, where the waves interfere constructively-and in theory you could modulate this pulse to transmit a signal. No one outside the target area would be able to intercept it.
Not surprisingly, Hewish's profound scepticism extends to the Oxford project. "I think it's a great pity they're wasting their time on this." Other astronomers take a slightly different view. "The physics is right: there's nothing wrong with it," says Melrose. "I just don't believe that this mechanism can be set up and sustained in a pulsar." In that case, the new transmitter could still work-even if its inspiration proved to be false.
"This is the most exciting experiment that I have worked on," says Arzhang Ardavan. "Whatever happens, it will open up research in a whole area of physics that people just haven't really considered before." Singleton says: "I see no reason why it shouldn't work. Let's suck it and see."
If the equipment does do something interesting when the switch is thrown, tighten your seat belts. Twenty-first century technology is about to lurch through the light barrier.
Tackling the pulse
How do pulsars generate their regular blasts of radio waves? Astrophysicists believe that electrons and other charged particles travelling at close to the speed of light surround these compact stars. The particles are confined to curved paths by a powerful magnetic field. It is this motion that makes the electrons emit radio waves.
But the pulses we see are staggeringly powerful. To give off so much energy, these flying electrons would have to have an absurd amount of energy, equivalent to a temperature a billion billion billion times hotter than the Sun. Instead, most physicists agree that the electrons must be collaborating. Somehow, bunches of electrons are emitting electromagnetic waves all together, so that the waves interfere constructively, massively increasing the brightness of the pulse.
One idea is called the "streaming" model: electrons streaming through the ionised gas around the neutron star hit turbulence and clump together. As the clump spirals around in the magnetic field, every electron will give off waves at once. In an alternative idea developed by Malvin Ruderman of Columbia University in New York and Peter Sutherland of McMaster University in Hamilton, Ontario, small clouds of electrons are created by single, highly energetic particles. This is know as the "spark gap" model. But most astrophysicists find these models rather contrived-cobbled together to fit the data, rather then following naturally from the known properties of pulsars.
Nick Appleyard and Bridget Appleby are science writers based in Bristol
From New Scientist magazine, vol 170 issue 2288, 28/04/2001, page 28
Rival particle smashers set out on collision course 31 Mar 01
IT'S just a gleam in the eyes of physicists now, but a state-of-the-art linear particle accelerator could be built in Germany, the US or even Japan. Scientists are vying for the chance to host a new particle smasher that could shed light on conditions in the Universe a split second after the big bang.
"People seem to have the feeling that only one or maybe two will be built," says Gerhard Materlik of the DESY accelerator lab in Hamburg. "I'm sure that at least one of them will be built-we hope in Hamburg."
Last week, DESY published plans for a new collider called TESLA (TeV-Energy Superconducting Linear Accelerator). The accelerator would use superconducting magnets to accelerate beams of electrons and their antiparticles, positrons, smashing them into each other at energies of 500 billion electronvolts-five times that achieved in similar machines so far. This would recreate the conditions that existed 10-12 seconds after the big bang.
Scientists think this accelerator would complement the ring-shaped Large Hadron Collider, which is being built near Geneva. If the LHC identifies exotic particles such as the Higgs boson, a hypothetical particle that would clarify what gives particles mass, TESLA could pin down its properties in detail. Construction could begin as early as 2003.
Plans for a linear collider in the US were the hot topic at a workshop last week at Johns Hopkins University in Baltimore. "The overwhelming consensus was that people loved the idea," says Morris Swartz of Johns Hopkins, who organised the meeting. "Were we to lose the next big project, then our domestic programme would be harmed."
Although it would probably use different technologies, the American collider would smash particles together at about the same energies as TESLA. Japanese scientists are also proposing a similar accelerator. All three could be completed by 2010.
From New Scientist magazine, vol 169 issue 2284, 31/03/2001, page 6
Cracked it? 31 Mar 01
Hold the bubbly until we're sure this superconductor really works
SUPERCONDUCTIVITY is creating a buzz again with the announcement of a new material that is said to have zero electrical resistance at room temperature. The claim, from researchers in Croatia, comes just a few weeks after the discovery that the simple chemical magnesium diboride superconducts at temperatures up to almost twice those needed for other metallic superconductors to work (New Scientist, 3 March, p 6).
The Croatian scientists say that current will flow effortlessly through their material, a mixture of lead carbonate and lead and silver oxides, at up to about 30 °C. "These results are suggestive of a transition to a superconducting state," says Georg Bednorz of the IBM Zurich Research Laboratory, who shared the 1987 Nobel physics prize for discovering cuprate superconductors. But because of numerous false alarms in this field, researchers are treating the announcement with caution, especially as no one has yet managed to reproduce the results.
Danijel Djurek, a physicist at A. Volta Applied Ceramics in Zagreb, Croatia, claims that he discovered his superconducting ceramic mixture in the late 1980s. But he was unable to pin down the structure and formula of the material, and his research was interrupted by years of war, following Croatia's split from Yugoslavia. Now Djurek and his team say they have finally hit on a formula that works reliably and reproducibly at room temperature.
Some telltale signs of superconductivity are easy to spot. For example, a graph of resistance plotted against temperature shows a characteristic drop at the temperature at which the material becomes superconducting. Physicists usually require other evidence too, such as the ability to expel all magnetic fields. Djurek's material seems to do this too.
Archie Campbell, director of Cambridge University's Interdisciplinary Research Centre in Superconductivity, says the data clearly shows the hallmark of a superconductor. "This is not a small effect. There's no room for misinterpretation," he says, adding it's either superconductivity or it's a mistake. Nevertheless, all the researchers contacted by New Scientist were extremely reluctant to start popping corks. "I have some concerns which keep my enthusiasm on a moderate level," says Bednorz.
The biggest question mark hangs over the failure of other groups to replicate the results. Paul Chu, director of the Texas Center for Superconductivity at the University of Houston, has been following Djurek's work for some time. "We recently tried to use his new formula but failed to reproduce his results," says Chu. "I think we will try a little more. It's too important to ignore." Djurek has raised some doubts by not yet supplying other labs with samples prepared by his team. He says he will have them ready in two or three weeks.
Robert Cava of Princeton University is highly sceptical, however. He points out that dozens of groups around the world reproduced magnesium diboride's superconductivity within a few weeks of the discovery being announced. The world has had plenty of time to reproduce Djurek's results but found nothing, Cava says.
From New Scientist magazine, vol 169 issue 2284, 31/03/2001, page 7
Quantum mischief 17 Feb 01
The smaller micromachines get, the harder it is to control what they do
A WEIRD quantum effect could come to plague designers of micromachines, say scientists at Bell Labs in New Jersey. They have found that a phenomenon known as the Casimir effect can make parts of a microscopic see-saw move spontaneously.
Engineers will have to take the Casimir effect into account, they say, or else the revolutionary molecule-sized machines now being planned could come unstuck. But there's a plus side too: the effect could be harnessed to form a nano-scale spring.
Nanotechnology is an emerging field in which scientists hope to build machines that have parts just a few thousand atoms across. Such devices could one day cruise your bloodstream dispensing drugs, or patrol your mattress exterminating bed bugs.
But when nano-devices are built small enough, previously ignored quantum effects come into play, says Hobun Chan at Bell Labs, part of Lucent Technologies. The phenomenon he's worried about was predicted in 1948 by the Dutch physicist Hendrik Casimir, who reasoned that in the quantum world even a vacuum isn't devoid of energy.
Instead, it contains virtual photons and other particles which pop in and out of existence. But in a small space, only photons whose wavelengths fit into the space a whole number of times can appear. As a result, the gap between two very closely spaced uncharged plates in a vacuum contains fewer particles than the space outside. Casimir reasoned that this difference should create a pressure that pushes the plates together. Steve Lamoreaux at Los Alamos National Laboratory in New Mexico eventually demonstrated Casimir's effect in 1996 by measuring the attraction between two very closely spaced plates (New Scientist, 25 January 1997, p 16).
Chan and his colleagues wondered what this effect might do to micromachines. To find out, they manufactured a tiny see-saw (see Diagram), to see if it was affected by quantum fluctuations in the vacuum. Chan slowly lowered a conducting sphere towards the see-saw. At a distance of about 500 nanometres, the see-saw began to swing towards the sphere, until they touched. Similar distances would commonly separate the components in many micromachines now being designed, Chan warns. "It could certainly lead to malfunction."
And the smaller the machine, the worse the problem gets. "At a separation of 10 nanometres, the pressure is as much as 1 atmosphere," he says.
Boris Spivak, an expert on quantum effects in metals at the University of Washington in Seattle, says the Bell Labs work-to be published in the journal Science-could help reveal how heat and gravity affect micromachines. "It's fantastic they had the sensitivity to measure this," he says.
But the Casimir effect could also prove useful in nano-design. It might be possible, says Chan, to make a switch that clamps shut in response to the subtle vibrations of background noise. Lamoreaux is more enthusiastic. "It's a ready energy storage mechanism, you can use it anywhere you need a spring," he says.
Eugenie Samuel, Boston
From New Scientist magazine, vol 169 issue 2278, 17/02/2001, page 22