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Iraqi wetlands face total destruction Dams and drainage projects have all but wiped out a vast ecosystem NS 19 May 2001

ONE of the world's largest marshes, home to the Marsh Arabs of southern Iraq, has all but disappeared over the past decade, according to satellite images released this week by the UN Environment Programme. UNEP's director, Klaus Toepfer, describes the loss as "a major ecological disaster, comparable to the drying of the Aral Sea and the deforestation of Amazonia". But claims that this environmental and human disaster is largely due to drainage projects carried out by Saddam Hussein in the aftermath of the Gulf War were contested by hydrologists this week. They say that dams built by Turkey in the headwaters of the rivers Tigris and Euphrates, which feed the marshes, are at least as much to blame as drainage. The images of the desiccated marshes of southern Iraq are among a batch of 16,000 pictures of environmental degradation across the planet taken by American Landsat remote-sensing satellites. NASA donated the images to UNEP, which released them alongside the report An Ecosystem Falls Apart:

Toepfer says the images "show that around 90 per cent of this special wildlife habitat, home to rare species and peoples with a 5000-year cultural history, has been lost as a result of human impacts including extensive drainage". Until the 1970s, the freshwater marshes covered up to 20,000 square kilometres. As well as providing farming and fishing grounds for the Marsh Arabs, the wetlands underpin up to 40 per cent of Kuwait's shrimp catch: the crustaceans spawned in the marshes before juveniles headed downstream to the Gulf. But since then, dams and drainage projects have cut off the water supply., Major losses are thought to have occur-red in the early 1990s, when Saddam built a huge network of dams, embankments and canals in and around the marshes (New Scientist, 17 April 1993, p 11). Some drained the marshes; others diverted the rivers Tigris and Euphrates along canals, including a giant "third river", which prevented the rivers from spilling into the marsh areas during the wet season.

Iraq said the works were designed to drain salt from agricultural soils, which made them impossible to cultivate. But humanrights activists claimed Saddam was trying to drive out the Marsh Arabs, who lived in reed houses on artificial islands in the marshes, and who had rebelled against his regime in 1992. Most have since left, and much of the marsh is now reported to be a salt-encrusted desert.

But some hydrologists, including those employed by supporters of the Marsh Arabs, now conclude that Saddam is not wholly to blame. British hydrology consultant Ron Manley has advised the European Union and the AMAR appeal for the Marsh Arabs on the issue. He calculates that Turkish dams built in the late 1980s and early 1990s have cut the annual flow of the Euphrates by more than 20 per cent, and could eventually halve the flow. "The storage capacity of [all] the dams on the Euphrates is six times greater than the river's annual flow," concludes the UNEP report. The dams divert water for irrigation across eastern Turkey, Manley says. Dams planned for the Tigris, including the controversial Ilisu dam being promoted by British engineering companies, would further reduce flow to the marshes. But the absolute cut in river flows is not the main problem, Manley told New Scientist. What's more important is that the dams have .eliminated the spring flush of floodwaters, on which the marshes depended to survive". Stopping the spring flood has dried up threequarters of the marshes, he says. Saddam has done the rest.

Without the dams, Saddam's drainage works would not have been possible at all, Manley adds. By reducing the peak water flows, the dams "created a situation where it was possible to carry Qat engineering works in the marshes".

Manley is sure the dry weather is not to blame. "Turkey claims that the reduced river flows are caused by drought. But if you look at the rainfall data for the catchment, there is no significant change." Fred Pearce

Nuclear warning NS 19 May 2001
Russia's defence systems are in a dangerous state of decay

AS RUSSIA struggles to restore links with four military satellites following last week's fire at a relay station, experts say the incident illustrates the advanced decay of Russia's space-based defences. They warn that Russia's inability to detect US missile launches from space could inadvertently cause a nuclear war.

Anatoly Perminov, head of Russia's Space Forces, has admitted that the fire at a satellite relay station in Serpukhov, 200 kilometres south-west of Moscow, prevented data being downloaded from four military satellites for a day. He declined to say what the satellites were for.

One may have been Russia's sole surviving early-warning satellite, designed to detect missile launches from the US. There used to be nine circling in high orbits from which at least one could always see any telltale plume of heat over US missile sites. The surviving satellite, says Geoffrey Forden of the Massachusetts Institute of Technology, allows Russia to monitor the US for a mere six hours a day.

"That is frightening," says Forden. He says early-warning satellites have saved the world from nuclear war three times after ground-based radars detected possible missile attacks-twice in the US and once in Russia. The satellites reassured the military that there had been no launches. Forden says that the most recent irrcident, in 1995, was sparked by a research rocket launched from Norway. Russian president Boris Yeltsin convened his nuclear emergency command. "But in 1995, the full fleet of early-warning satellites kept a 24-hour watch on US missile fields," says Forden. They saw no follow-up missile launches from the US, and Yeltsin stood down his forces.

"That early-warning capability may well have prevented nuclear annihilation," writes Forden in a report this month for the Cato Institute, a defence think tank in Washington DC. "If another benign event sets off the nuclear alarm, the Russians no longer have the fleet of satellites to reassure them."

Russia has six new early-warning satellites ready for launch, but the military is spending its limited funds elsewhere.

Forden says that in its own interests, the US should pay Russia the $160 million needed to launch enough satellites to give it a continuous view of US missile sites. Another $340 million would complete the joint Russian-American Observation Satellites project, which was started in 1992 to develop better space-based missile detection, but is now languishing for lack of funds. Debora MacKenzie More at:

Shotgun wedding NS 19 May 2001
If you sequence in haste will you end up repenting at leisure?

CELERA, the company which shared the glory for sequencing the human genome last summer, now faces claims that its data may be riddled with errors.

As many as half the company's gene sequences for the fruit fly may contain mistakes, says Samuel Karlin, a mathematician at Stanford University in California. His work suggests there might be many errors in other genomes that have been sequenced using similar techniques, he says.

But others have defended the results. "I would take 50 per cent correct as a compliment, not a criticism,' says Gerry Rubin of the US's fly-sequencing programme at the Howard Hughes Medical Institute in Berkeley. An update next year should improve its accuracy to 75 per cent, he says. Rubin was one of the coauthors when the head of Celera, Craig Venter, published the full sequence of the fly genome in Science in March 2000. The work was hailed as a vindication of the 'pure shotgun sequencing" technique the company used, where copies of a creature's DNA are broken into little pieces and sequenced. Computers then assemble the full sequence by looking for overlapping fragments.

But when Karlin began to use Celera's fly genome, he spotted lots of errors. 'More than 60 per cent of their sequences were in substantial disagreement [with known sequences], and this got me a little bit angry," he says. So he did a fuller analysis with his colleagues. They hunted through Celera's genome for 1049 fly genes whose sequence and function had already been worked out and carefully checked in experiments.

Although 26 per cent of the genes were exact matches, and a further 29 per cent accurate to within 1 per cent, the remaining 45 per cent contained a range of moderate to serious errors-or were missing altogether. "We couldn't find a lot of the genes we were working on ourselves," says Karlin. Other errors included the omission of entire proteincoding segments of genes, or exons, while other genes had been 'read" from the wrong starting point.

Karlin claims there could be worse errors in both the public and private versions of the human genome. 'Everyone was rushing," he says. But the public project relied on a slower, more accurate version of shotgun sequencing-and Celera ended up including a substantial amount of data from the public project in its version (New Scientist, 17 February, p 4).

Meanwhile, Karlin warns researchers to take care if they're studying any "new" genes revealed by Celera. "My advice is to do whatever part you're working on again," he says. His analysis reveals the perils of relying too much on computers, Karlin says. 'People are trying to get away without doing experiments."

Celera plays down the criticisms. "We never said that the fly genome was totally and 100 per cent complete," says spokeswoman Heather Kowalski. "Annotation and analyses of genomes can go on for decades."

Karlin's work appears in Nature (vol 411, p 259). He initially sent his paper to Science but the joumal didn't publish it. 'They sat on it for five months,' he says. Andy Coghlan

Exploding the myth NS 19 May 2001
Shortcomings in a database created false booms in species diversity

A NEW analysis of the fossil record casts doubt on the long-held assumption that biodiversity has been steadily rising for millions of years. If the findings are right, they could sink one of the major theories in the field of palaeobiology.

Until now, most researchers accepted that biodiversity mushroomed after a mass extinction 250 million years ago. But a new database of marine fossils suggests that levels of biodiversity have actually stayed largely unchanged since that time. The implications are huge, says John Alroy at the University of California at Santa Barbara.

"Our results, if correct, could have big implications on how we understand evolution," Alroy says. If biodiversity is static, he says, then it-and hence evolution-must be regulated more by predation and competition between species than by ecological factors such as climate. '

The evidence for an explosion in biodiversity comes from another database of 30,000 marine fossils set up in the 1970s by palaeobiologist Jack Sepkoski, then at the University of Chicago. To cope with the limited computing power available at the time, Sepkoski simplified the data by recording only the dates of a species' appearance in the fossil record without noting population sizes.

Such short cuts created substantial biases. For example, the apparent explosion in diversity 250 million years ago could be an artefact of the sheer number of fossils recovered from that period.

To address these problems, a consortium of palaeobiologists led by Alroy and Charles

Marshall at Harvard University revamped the database by compiling data on thousands of fossilised clams, molluscs and other marine invertebrates. They divided the prehistoric record into discrete 10-million-year time slots and used statistical sampling to gauge the number of species in each slot.

They looked at two time periods. The first, 460 to 300 million years ago, included the Palaeozoic "plateau", when biodiversity supposedly stayed constant after the Cambrian explosion 540 million years ago. The other was the late jurassic to early Palaeogene period, 164 to 24 million years ago, when accepted theories say species diversity ballooned.

Using the revised database, the researchers applied eight sampling methods aimed at reducing bias. Overall they confirmed that biodiversity stayed constant or even decreased during the Palaeozoic plateau. Results varied depending on the sampling method used, but in one model, the late jurassic explosion vanished altogether. The researchers saw at most only a small rise in biodiversity during the Jurassic to Palaeogene period.

The database covers only marine fossils from the northern hemisphere, but the researchers plan to fill in the gaps. They will analyse the Cambrian explosion next.

More work needs to be done. But "if these results stand up to further analysis, they will quite substantially change our picture of the pattern of biodiversity", says Mark Newman, a palaeontologist at the Santa Fe Institute in New Mexico. Catherine Zandonelia

More at: Proceedings of the National Academy of Sciences (vol 98, p 6261)

The awful truth NS 19 May 2001
Why would anyone in their right mind want to clone a baby when animal cloning can go disastrously wrong?

ZITA the supercow was a beast in a million, the highest-ranked Holstein in the US. In her prime her milk yield was nearly twice the average, and cattle breeders paid top dollar to get her genes into their herds. Then, alas, she got old and died. But dry your eyes. This is the age of the clone, and the genetic blueprints of prize cows can now be saved from the grave. Grazing on a farm in Maryland are Zita-2 and Zita-3, two three-month-old calves cloned using two cells from Zita's ears.

American cloning companies are busy making multiple copies of just about every top pedigree cow and bull in the land. In time, they hope identikit supercows and superbulls will be bred, milked and even butchered for profit, just like the old ones. "We're cloning some of the highest-level bulls and think we can sell hundreds,' says Ron Gillespie of Cyagra, the Massachusetts company that cloned Zita. For prize breeding animals, which can fetch $40,000 or more, cloning is economic even at today's going rate of $15,000 to $25,000 per cow. And as more animals are cloned, the cheaper it will get. 'Push the price down to $10,000 and there would be 100,000 animals that it would be economic to clone, and in the $5000 range, millions."

That's millions of cloned cows and bulls. Created just to make food. In the US alone.

Ever since Dolly the sheep was born, fears about cloning have been tempered by hopes that the technology will one day save thousands of human lives. And so it might. Already cloning is enabling scientists to produce animals capable of secreting valuable drugs in their milk, and to look for ways to clone tissues for transplantation. But developing these medical spin-offs could take up to 10 years. Cloned beef steaks and milkshakes could be with us much sooner.

So far, it's the baby cloners who have been in the firing line. Now, as companies like Cyagra forge ahead, the prospect of cows being cloned en masse for food is provoking alarm as well. And not just among animal welfare campaigners.

Ian Wilmut, the scientist who led the Dolly team, says it is vital that controlled farm trials of cattle cloning are carried out before any commercial production of cloned meat 4nd dairy food is allowed. Companies need to prove that large-scale farm cloning involves no undue animal cruelty, that clones are as healthy as ordinary animals, and that food from cloned animals and their offspring is as safe and nutrious as conventional food, Wilmut told New Scientist. The cattle cloners 'ought to be making systematic comparisons between clones and ani-' mals produced by embryo transfer, looking not just at their milk yield but also their health and lifespan". Until then, he says cloned food ought to be banned from shops and restaurants. "If companies start marketing this food and there are problems it will bring the whole technology into disrepute.' Herds of identical cloned animals would be a welfare disaster, says Joyce da Silva of Compassion in World Farming. "There would be a huge loss of genetic diversity with unforeseeable results in terms of animal illness." A more immediate fear is that four years on from Dolly, cloning is still a waste of animal life. For every Zita-2 or Zita-3, say scientists at the sharp end, scores of clones die in the womb or develop deformities, and even clones that look healthy could be 'ticking timebombs" destined to go awry. Until recently, the full extent of the problem was hidden, largely because the cloned animals that don't survive don't get much space in scientific papers. A rare exception is a 1999 paper that appeared in the journal Theilogenology (vol 51, p 1451) under the heading "Clinical and pathological features of cloned transgenic calves and fetuses". The paper is an eye-opener. Take the short life of "calf 1 ". Its placenta was bloated with six times the fluid of a normal pregnancy. Yet at birth it appeared normal. It mooed, started breathing and tried to stand. But appearances were deceptive. Its blood oxygen levels were one-third of what was expected, and carbon dioxide was up to three times normal. A day later, oxygen was pumped into its lungs and it was sedated with valium, but to no avail. The calf was soon dead. Its lungs had never properly inflated, it had an enlarged heart, and its liver, which should have been a smooth crimson organ, was a roughened orange slab. And those, remark some cloners wryly, were the 'good old days'. "We saw consistent defects, so we thought we'd find consistent solutions," says Jim Robl of the Massachusetts-based company Hematech. Oversized calves, lung and heart problems were the major themes. But now the more cloners you talk to, the longer the list of defects you hear about: enlarged tongues, squashed faces, bad kidneys, intestinal blockages, immune deficiencies, diabetes and shortened tendons that twist the young animal's feet into useless curves. 'There's no pattern,' says Robl. "It's perplexing."

Nor are the clones the only victims. The cow that carried calf 1 suffered a fatal fall in blood pressure after the birth. In fact, 4 of 12 surrogate mothers in the study died from pregnancy complications. Such deaths still happen despite improvements to cloning, says Michael Bishop of Wisconsin-based cloning company Infigen. "We sacrifice the cow and the clone. . . all the heroics in the world can't rescue those animals.'

Despite this, some commercial cloners claim that cloning is no more wasteful than cattle breeders' standard artificial insemination methods. The figures to date suggest otherwise. While artificial insemination has a 40 per cent success rate, at best only 5 to 10 per cent of implanted cloned embryos become live calves. Around 75 per cent die in the first two months of pregnancy but miscarriages and terminations happen right to the end. And every fourth clone born is either stillborn or suffers from a lethal defect.

Even clones that survive and look healthy may harbour subtle defects. When Jon Hill from Cornell University examined the behaviour of newborn cow clones, he found they scored lower on average than typical cows in tests of attentiveness and intelligence. And mouse cloners say that one in three clones born looking normal become massively overweight a few weeks later. "Researchers who study obesity in mice say they have never seen such fat animals," says Ryuzo Yanagimachi of the University of Hawaii at Manoa.

Yanagimachi's team is now taking a close look at gene activity in newborn mouse clones. And things aren't looking good. 'All cloned babies have some sort of errors," he says. 'I'm surprised they can survive it.'

Of course in some species, they don't survive at all-witness the countless failed attempts to get cloned cat and dog embryos to develop into living, breathing animals.

Back at the cloning companies, scientists see this outbreak of negativity as little more than propaganda orchestrated to put off the baby cloners. What happens with mice is no guide to what happens in other animals, insists Robert Lanza of Advanced Cell Technology in Worcester, Massachusetts. Lanza says his company has carried out fresh, and as yet unpublished, tests on virtually every surviving cow it has cloned and claims they are healthy and normal. 'People have said they don't believe there is a single normal clone alive. That is just total nonsense." In any case, say the cattle cloners, even if clones are quite different from other animals, that doesn't make them unhealthy. Infigen has amassed a huge database of blood tests from apparently healthy cloned cows. "The data suggested to the vets that some of them should be dead," says Infigen's Michael Bishop. "I think that shows we don't really know what normal is."

Perhaps. But whether that is the sort of reassurance needed to silence the sceptics seems debatable when even small imbalances in hormones, proteins or fat levels could alter the quality of milk and meat. According to Britain's Food Standards Agency, in Europe cloned meat and milk would be classed as novel foods and so sellers would need a special licence. But unlike GM foods, there is no legal requirement for cloned food to be labelled. And nothing to stop British farmers importing cloned cattle.

Meanwhile, there's one thing virtually every animal cloner agrees on: human cloning ought to be unthinkable. The idea of screening cloned embryos for chromosomal abnormalities, and using imaging to keep tabs on the fetus, is "sheer nonsense", says Don Wolf, who is attempting to clone monkeys at the Oregon Regional Primate Research Center in Beaverton. Fetuses that look robust at 60 days may die at 61. And a clone that dies after five days of life can have normal chromosomes and genes while still in the womb. "How in the world," asks Wolf, "will they screen out problems when they don't know what to look for?'

So far that question has been aimed only at the baby cloners. One day it could be on the lips of shoppers faced with shelves bulging with milk and meat from cloned supercows. Philip Cohen and David Concar

Multiple Universes NS 19 May 2001

ELVIS is still alive, say a pair of respected cosmologists. Not only that but Marilyn Monroe came up with the theory of relativity, the dinosaurs survived and went on to invent the automobile and Al Gore, not George Bush, is the US President. "In fact, as long as a history is consistent with the laws of physics, it will not only happen but happen an infinite number of times," says Alexander Vilenkin of Tufts University in Medford, Massachusetts. it seems far-fetched but Vilenkin and jaume Garriga of the independent University of Barcelona say it's just a logical consequence of "inflation"-the most widely accepted model of the Universe's birth. Inflation says the early Universe expanded extremely rapidly. This expansion was so fast, the researchers believe, that distant regions of the Universe have been entirely isolated from each other ever since, because light hasn't had time to travel between them.

Because of the inherent quantum randomness involved in the formation of stars and galaxies, each of these "O-regions" should develop differently-and have a different history. Because inflation also predicts that the Universe is infinite, this means there are an infinite number of 0-regions too. But Vilenkin and Garriga wondered if the number of possible histories is also infinite. They reasoned that you cannot examine a particular 0-region in infinitely fine detail. There is a quantum "graininess" to space that makes it impossible to tell apart histories that are very similar to each other. "We calculate that there cannot be more than 10 to the power of 10110 distinct histories," says Vilenkin. "It's a fantastically huge number but it isn't infinite." So, if there are an infinite number of 0-regions but a finite number of histories, every possible version of history will occur, and it will occur an infinite number of times.

'Not only is Elvis still alive but an infinite number of Elvises are still alive," says Vileinkin. Vilenkin admits that this might cause people to take a fatalist view of existence. Although there may be 0-regions where tax does not exist, there may be others where Hitler won the Second World War or the Cuban missile crisis led to global annihilation. "I find the idea that all bad things happen very depressing I admit," says Vilenkin. Alan Guth of the Massachusetts institute of Technology, the "father" of inflation, doesn't offer any get-out. "I don't see any weaknesses or flaws in the work," he says. So if inflation is correct-and several experiments recently gave it StTong support (New Scientist, 5 May, p 6)-the worst may already have happened somewhere out there. And, as light continues to travel further and further, 0-regions will continue to grow and increasingly to overlap. Marcus Chown more at:

Time Travel NS 19 May 2001
RONALD MALLETI thinks he has found a practical way to make a time machine. Mallett isn't mad. None of the known laws of physics forbids time travel, and in theory, shunting matter back and forth through time shouldn't be that difficult. The catch usually comes when you try to make it work in practice. Remember wormholes, those clever little tunnels in space and time that can supposedly be used to travel from one moment to another? On paper, they're a perfectly respectable way to travel back in time. Trouble is, you need a supply of exotic "negative energy' matter to prise your wormhole open.

But Mallett, a professor of theoretical physics at Connecticut University, believes he has found a route to the past that uses something much more down to earth: light. Mallett has worked out that a circulating beam of light, slowed to a snail's pace, just might be the vital ingredient for time travel. Not only is the technology within our grasp, Mallett has teamed up with other scientists at Connecticut to work towards building it. "With this device,' he says, 'time travel may become a practical possibility."

It may be hard for us to climb into Mallett's time machine, as slowing light down requires temperatures close to absolute zero. But future, advanced civilisations might work out a way to do it. And they might even come back to tell us how. If it works in the way Mallett believes it might, his device would provide time travellers from the future with their first gateway into our history.

Mallett began his journey into the past when he was just ten years old. In 1955, his father died of a heart attack. "For me, the sun rose and set on him. It completely devastated me,' Mallett says. But then he came across The Time Machine by H. G. Wells. Even as a child, Mallett knew his father hadn't taken care of himself. Drinking and heavy smoking took d toll on his weak heart, and it gave out at the age of 33. "My notion was that if I could build a time machine, I might be able to warn him about what was going to happen,' Mallett says. "That became my guiding light."

What started as a childish notion grew into a passionate investigation of everything ever written about time travel. When Mallett studied the work of Einstein-who died in the same year as his father-he realised that Wells's novel was right on track: time travel is, in theory at least, achievable. Einstein himself found the notion upsetting, but he had only himself to blame. He showed that the effect we call gravity is a bending of space and time. Anything that has mass or energy distorts the space and the passage of time in its vicinity, a bit like the way the surface of a soft couch is distorted when someone sits on it. Solving Einstein's gravitational field equations tells you just how space-time is distorted by mass and energy.

A lump of matter stretches space and time. So, for example, clocks run slower in the gravitational field close to Earth than they do far out in space. And if you set a massive lump spinning, it begins to whip space and time around after it, like a rotating teaspoon dragging the foam on a cup of coffee. The denser and faster-moving the matter, the more strongly it distorts space-time.

Take this idea far enough, and you find that time can be twisted so much that instead of running in an infinite line from past to future, it is bent into a ring. Follow this loop around, and you return to a particular moment, just as a walk around the block brings you back to your front door. Theoreticians have found some solutions to Einstein's equations that include these 'closed time-like loops"-physicists' jargon for a time machine. The first to do so was the Austrian-born mathematician Kurt Godel, in 1949, but unfortunately his solution required the whole Universe to be rotating-which it's not. Decades later Kip Thorne of Caltech came up with the idea of using wormholes, which link different regions of warped space-time, to provide such loops. Other loops can be made by infinitely long, spinning cylinders-somewhat hard to come by-or fast-moving cosmic strings. In the early Universe, these ultra-dense strands of matter may have been as common as dirt, but alas, no longer.

Mallett's idea of using light is much less outlandish. 'People forget that light, even though it has no mass, causes space to bend," he says. Light that has been reflected or refracted to follow a circular path has particularly strange effects. Last year, Mallett published a paper describing how a circulating beam of laser light would create a vortex in space within its circle (Physics Letters A, vol 269, p 214). Then he had a eureka moment. "I realised that time, as well as space, might be twisted by circulating light beams," Mallett says. To twist time into a loop, Mallett worked out that he would have to add a second light beam, circulating in the opposite direction. Then if you increase the intensity of the light enough, space and time swap roles: inside the circulating light beam, time runs round and round, while what to an outsider looks like time becomes like an ordinary dimension of space. A person walking along in the right direction could actually be walking backwards in time-as measured outside the circle. So after walking for a while, you could leave the circle and meet yourself before you have entered it (see Diagram, opposite).

The energy needed to twist time into a loop is enormous, however. Perhaps this wouldn't be a practical time machine after all? But when Mallett took another look at his solutions, he saw that the effect of circulating light depends on its velocity: the slower the light, the stronger the distortion in spacetime. Though it seems counter-intuitive, light gains inertia as it is slowed down. "Increasing its inertia increases its energy, and this increases the effect," Mallett says. As luck would have it, slowing light down has just become a practical possibility. Lene Hau of Harvard University has slowed light from the usual 300,000 kilometres per second to just a few metres per second-and even to a standstill (New Scientist, 27 January, p 4). "Prior to this, I wouldn't have thought time travel this way was a practical possibility," Mallett says. "But the slow light opens up a domain we just haven't had before."

To slow light down, Hau uses an ultracold bath of atoms known as a Bose-Einstein condensate. "All you need is to have the light circulate in one of these media," Mallett says. "It's a technological problem. I'm not saying it's easy, but we're not talking about exotic technology here; we're not talking about creating wormholes in space.' Mallett has already caught the interest of his head of departipent, William Stwalley, who leads a group of cold-atom researchers. Their first experiment will be designed only to observe the twisting of space, by looking for its effect on the spin of a particle trapped in the light circle. If they can then add a second beam, Mallett believes evidence of time travel will eventually appear. He's not sure how time travel would manifest itself. Perhaps what starts out as a single trapped particle would acquire a partnerthe particle visiting itself from the future.

Stwalley is more interested in the practical challenges of the experiment, and remains sceptical about possibilities of time travel.

"A time machine certainly seems like a distant improbability at best,' he says.

Last month, Mallett gave his first talk on the idea at the University of Michigan at the invitation of astrophysicist Fred Adams, who accepts that the theoretical side of Mallett's work stands up to scrutiny. "The reception was cautious and sceptical," Adams admits. 'But there were no holes punched in it, either. The solution is probably valid."

But even Adams isn't convinced that the experiment will work. That's hardly surprising, as time travel raises disturbing questions. Could you go back and murder your grandparents, making your birth impossible? There may be ways out of this problem (see 'Paradox lost"), but most physicists think that any attempt to mess with history should be impossible. The Cambridge astrophysicist Stephen Hawking calls this the .chronology protection conjecture".

The general theory of relativity, which Mallett used to work out his theory of time travel, does not take account of quantum mechanics. Could this be the crucial omission that means time machines won't work in the real Universe? Hawking and Thorne say that any time machine would magnify quantum fluctuations in the electromagnetic field, and destroy itself with a beam of intense radiation. But to know for sure, we need a theory of quantum gravity-a theory that merges quantum theory with relativity.

Even Mallett doesn't claim that time travel is definitely within reach. 'Whether it will do what I predict is something that one will only know by performing the actual experiment,' he says. Then there's the problem of getting on and off the loop of time without destroying it-or yourself. "I really don't know whether you could use this in the sense of

H. G. Wells's time machine," says Mallett. But who knows? In a few years, we may have entered an era when time travel is possible, and all kinds of strange people, things and situations from the future might come to visit. One thing seems certain, though. Even if the Connecticut time machine works, it won't be taking any Yankees back to the court of King Arthur. Mallett's circle of light won't allow anyone to travel back beyond the point where time first formed a closed loop. So it will be impossible to go back to a time before it was set up. 'A later person could only travel back to the time when the machine is turned on," Mallett says. This may explain why we have never been overrun by visitors from the future.

It also means that although Mallett might change the Universe, he won't ever achieve his childhood dream. Mallet's father will remain forever beyond his reach.

The World's Oldest Shamans? NS 19 May 2001
Could mysterious figures lurking in Australian rock art be the world's oldest shamans? Alan Couke investigates

ALL eyes are on the shaman: arms outstretched, head back, her face hidden behind a mask. She wears a long, tapering cap, and clutches a short wand in each hand. There are tassels at her hips and elbows, and these jump as she begins to move. The crowd around her watches, spellbound, as she embarks upon her journey to the spirit world.

That's one possible interpretation of a scene recorded thousands of years ago on a remote rocky outcrop in north-west Australia. The painting is part of a vast collection that opens a window on an ancient hunter-gatherer society that may date back to the last ice age. Despite the quality and extent of this record, much about the paintings remains a mystery. Who were the artists? When were the paintings done-and what do they mean?

The suggestion that this rock art may be the oldest known depiction of a shamanistic ritual comes from a group of researchers led by Per Michaelsen, a geologist at James Cook University in Queensland. They argue that these ancient paintings may represent not only early religious practices, but perhaps also a cultural heritage common to all humans. Such daring new theories do not go down well with the rock-art establishment, especially as Michaelsen and his colleagues are newcomers to the field. But regardless of which ideas prevail, the controversy is cer tain to attract attention to arb astonishing record of a vanished people.

The Bradshaws, as the paintings are collectively known, were first noted by Europeans in 1891 and take their name ftom Joseph Brad shaw, the rancher who described them. They are found in a region known as the Kimberley, a remote place even by Australian standards. The Kimberley lies at the northern end of Western Australia and is around twice the size of Britain with fewer than 40,000 inhabitants. It is a rugged sandstone landscape of plunging canyons and treacherous swamps. There are few roads and tropical monsoons make the interior inaccessible for much of the year.

Michaelsen estimates that there may be as many as 100,000 Bradshaw "galleries" tucked under rock overhangs along the region's major river systems. Many of the paintings have never been studied. But observations made by other researchers over the past few decades reveal several distinct artistic styles. Researchers recognise at least four major periods which they can place in chronological order by looking at patterns of weathering and instances where one style is superimposed upon another.

The oldest and largest paintings, which are up to 1. 7 metres tall, are known as the tasselled figures. They are the most realistic of the images and show figures in static poses in what appears to be ceremonial dress. The figures are characterised by large conical headdresses, and in patticular by tassels attached to the upper arms, elbows, hips and knees. The artists have taken great care to capture not only the ornamentation, but also the curves of the human body and anatomical details such as fingers and toes. In a few cases, the line of a nose or brow almost suggests a portrait.