Universe a grand tour of modern science Phần 9 docx

I n the late 1980s physicists at CERN, Europe’s particle physics lab in Geneva, began a long series of experiments aimed at simulating the Big Bang in little bangs hot and dense enough to set quarks free. These are the fundamental entities that constitute the heavy matter in the atomic nucleus. No one doubted by then that each of the protons and neutrons in a nucleus consists of three fundamental entities called quarks. Various experiments with particle accelerators had indirectly confirmed the presence of the quarks in the nuclear material. But no one had seen any free quarks. If you try to liberate a quark in ordinary reactions between particles, you unavoidably create a new quark and an antiquark. One of them immediately replaces the extracted entity. The new antiquark handcuffs the would-be escaper in a particle called a meson. This is the trick by which Mother Nature has kept quarks in purdah since the world began. To be more precise, the confinement of quarks began about 10 millionths of a second after the start of the Big Bang, at the supposed origin of the Universe. Before then, in unimaginably hot conditions, each quark could whizz about independently. Technically speaking, it was allowed to show its colour in public. By the colour of a quark, physicists mean a quality similar to an electric charge. But instead of just plus and minus, the colour charge comes in three forms, labelled red, green and blue. The quarks are not really coloured, but it’s a convenient way of thinking about the conditions of their confinement in ordinary matter. In a TV screen, a red, green and blue dot together make white, and the rule nowadays is that nuclear matter, too, must be white. That’s why protons and neutrons consist of three quarks apiece, and not two or four. One red, one green and one blue quark within each proton or neutron are held loosely together by particles called gluons. The colour force carried by the gluons operates only over very short ranges. Space is opaque to the colour force, in much the same way as frozen water is impenetrable by fishes. But at a high enough temperature space melts, so to say, and lets the colour force through. Then the quarks and gluons can roam about 604 as freely as do the individual charged atoms and electrons in the electrified gas, or plasma, of a neon lamp. The effect of the colour force is g reatly weakened because immediate neighbours screen each particle from the pull of distant particles. The resulting melee is called a quark—gluon plasma or, more colloquially, quark soup. Extremely high pressure may have the same effect as high temperatures, and physicists suspect that quark soup exists at the core of a neutron star, which is a collapsed star just one step short of a black hole. That’s what the theory says, anyway, but to set the quarks free experimentally required creating a new state of matter never seen before. I ‘A spectacular excess of strangeness’ A multinational team of physicists working at CERN set out to make quark soup by using an accelerator, the Super Proton Synchrotron, to melt the nuclei of heavy atoms. It was a matter of whirling heavy atoms up to high energy and slamming them into a target also made of heavy atoms—lead onto lead, for example. A direct hit of one nucleus on another would create a small fireball, and might briefly produce the extreme conditions needed to liberate quarks. The quarks would recombine almost instantly into a swarm of well-known particles and antiparticles, and fly as debris out of the target into detectors beyond. Only by oddities in the composition of the debris might one know that a peculiar state of matter had existed for a moment. For example the proportions of particles containing distinctive strange and charmed quarks might change. Charmed quarks are so heavy that they require a lot of energy for their formation, in the first moment of the nuclear collision. They would normally tend to pair up, as charmed and anticharmed quarks, to make a well-known particle called charmonium, or J/psi. But if conditions are so hot that plasma screening weakens the colour force, this won’t happen. The charmed quarks should enjoy a brief freedom, and settle down only later, in the company of lighter quarks. In the next moment of the nuclear collision strange quarks, somewhat lighter, are being mass-produced. By this time the colour force is much stronger, and it should corral the strange quarks, three at a time, to make a particle called omega. In shor t, the first signs of quark soup appearing fleetingly should be few charmoniums and many omegas. That was exactly what the CERN experimenters saw. By 1997 they were reporting a shortage of charmoniums among the particles freezing out of the supposed soup. Within a few years they had also accumulated ample evidence for a surplus of the strange omega particles. 605 quark soup ‘A spectacular excess of strangeness, with omega production 15 times normal, is just the icing on the cake,’ said Maurice Jacob of CERN, who made a theoretical analysis of the results of the nuclear collisions. ‘Everything else checks too—the relative proportions of other particles, the size of the fireballs, and so on. We definitely created a new state of matter, ten times denser than nuclear matter. And the suppression of charmonium showed that we briefly let the charmed quarks out of captivity.’ For the sake of only one criterion did the CERN team hesitate to describe their ‘new state of matter’ as quark soup, or to claim it as a true quark–gluon plasma. The little fireballs were not sufficiently hot and long-lived for temperatures to average out. It was like deep-frozen potage microwaved but not stirred, and in Switzerland no self-respecting cook would call that soup. I A purpose-built accelerator In 2000, colleagues at the Brookhaven National Laboratory on Long Island, New York, took over the investigation from CERN. Their new Relativistic Heavy Ion Collider was expressly built to make quark soup. Unlike the experiments at CERN, where one of the two heavy nuclei involved in an impact was a stationary target, the American machine brought two fast-moving beams of gold nuclei into collision, head-on. It achieved full energy in 2001, and four experimental teams began to harvest the results of the unprecedented gold-on-gold impacts. Before long they were seeing evidence of better temperature stirring and other signs of soupiness. These included a reduction in the jets of particles normally produced when very energetic quarks try to escape from the throng. In quark soup, such quarks surrender much of their energy in collisions. ‘It is difficult to know how the resulting insights will change and influence our technology, or even our views about Nature,’ commented Thomas Kirk of Brookhaven, ‘but history suggests there will be changes, and some may be profound.’ E For more about quarks and gluons, see Particle families. The supposed sequence of events at the birth of the Universe is described in Big bang. 606 quark soup I naway, Relativita ¨ tstheorie was always a poor name for Albert Einstein’s ideas about space, time, motion and gravity. It seemed to make science iffy. In truth, his aim was to find out what remained reliable in physical laws despite confusions caused by relative motions and accelerations. His conclusions illuminate much of physics and astronomy. Taken one by one, the ideas of relativity are not nearly as difficult as they are supposed to be, but there are quite a lot of them. One of the main theories is special relativity (1905) concerning High-speed travel. Another is general relativity (1915) about Gravity. Energy and mass appear in Einstein’s famous E ¼ mc 2 , which was a by-product of special relativity. It reveals how to get energy from matter, notably in powering the Sta r s and also Nuclear weapons, which were a fateful by- product. The equation implies that you can make new matter as a frozen form of energy, but when Paul Dirac combined special relativity with quantum theory it turned out that you inevitably get Antimatter too. Gener al relativity is another box of tricks, among which Black holes dramatize the amazing effects on time and space of which gravity is capable. They are also very efficient converters of matter into energy. Gravitational waves predicted by general relativity are being sought vigorously. More speculative are wormholes and loops in space, suggesting the possibility of Time machines. Applied in cosmology, Einstein’s gener al relativity could have predicted the expansion of the Universe, but he fumbled it twice. First he added a cosmological constant to prevent the expansion implied by his theory, and then he decided that was a mistake. In the outcome, his cosmological constant reappeared at the end of the 20th century when astronomers found that the cosmic expansion is accelerating, driven by Dark energy. Special relativity seems unassailable, but doubts arise about general relativity because of a mismatch to quantum theory. These are discussed in Gravity and Superstrings. 607 A t bogazko ¨ y in turkey you can still see the Bronze Age fortifications of Hattusas, capital of the Hittites. Suppiluliumas I, who reigned there for 40 years in the 14th century bc, refurbished the city. He came to a sticky end after the widow of Tutankhamen of Egypt invited one of his sons to marry her and become pharaoh. Opponents in Egypt thought it a bad idea and assassinated the Hittite prince. An ensuing conflict brought Egyptian prisoners of war to Anatolia. They were harbouring smallpox, long endemic in their homeland. The result was an epidemic in which Suppiluliumas I himself became the first victim of smallpox whose name history records. That was in 1350 bc. The last person to die of smallpox was Janet Parker of Birmingham, England, in 1978. She was a medical photographer accidentally exposed to the smallpox virus retained for scientific purposes. In the previous year in Merka, Somalia, a cook named Ali Maow Maalin had been the last to catch the disease by human contagion, but he survived. In 1980, the World Health Organization in Geneva formally declared smallpox eradicated, after a 15-year programme in which vaccinators visited every last shantytown and nomadic tribe. This was arguably the greatest of all the practical achievements of science, ever. Individual epidemics of other diseases sometimes took a high toll, including the bubonic plague that brought the Black Death to 14th-century Eurasia. Over all smallpox was the worst. Death rates in infants could approach 100 per cent, and survivors were usually disfigured by the pockmarks of the smallpox pustules, and often blinded. The historian Thomas Macaulay wrote of smallpox ‘turning the babe into a changeling at which the mother shuddered, and making the eyes and cheeks of the betrothed maiden objects of horror to the lover.’ Populations in Eurasia and Africa were left with a level of natur ally acquired immunity. But when European sailors and conquistadors carried smallpox and other diseases to regions not previously exposed to them, in the Americas and Oceania, they inadvertently wiped out most of the native populations. One victim was the Aztec emperor Ciutla ´ huac in 1520. Nor was it always inadvertent. ‘The devastating effect of smallpox gave rise to one of the first examples of biological warfare,’ noted the medical historians 608 Nicolau Barquet and Pere Domingo of Barcelona. In 1763 General Jeffrey Amherst, commanding the British army in North America, approved a proposal by Colonel Henry Bouquet to grind the scabs of smallpox pustules into blankets that were to be distributed among disaffected tribes of Indians. ‘You will do well to try to inoculate the Indians by means of blankets,’ Amherst wrote, ‘as well as to try every other method that can serve to extirpate this execrable race.’ By that time, many children in Eurasia were being deliberately infected with smallpox from very mild cases, in the knowledge that most would survive with little scarring and with acquired immunity. The practice of applying pus from a smallpox pustule to a child’s skin, and making a small cut, may have originated among Circassian women who supplied many daughters to Turkish harems. The wife of the British ambassador in Istanbul introduced the practice to London in 1721. It killed one in 50 of the children so treated and could itself be a source of contagion for others. I ‘Such a wild idea’ The Circassians were not the only women with a special reputation for beauty—meaning in those days, not pockmarked. Throughout rural Europe it was common knowledge that dairymaids often escaped the smallpox. English folklore attributed their good looks to their exposure to the morning dew when they went to milk the cows. As one song had it: Oh, where are you going, my pretty maiden fair, With your rosy red cheeks and your coal-black hair? I’m going a-milking, kind sir, says she, And it’s dabbling in the dew where you’ll find me. The dairymaids themselves had shrewder insight, and one of them pertly assured a Bristol doctor that she would never have the smallpox because she’d had the cowpox. This was a mild condition that produced sores on the hands of those dealing with cattle. The doctor’s apprentice, Edward Jenner by name, overheard this remark and remembered it. Three decades later, when he had his own practice in Berkeley, Gloucestershire, Jenner pursued the matter under the cloak of investigating diseases transmitted from animals to human beings. Eventually he steeled himself and his patients to see whether inoculation with the non-virulent cowpox might protect against smallpox. In 1796, in an experiment that would nowadays be called heroic, i.e. questionable, Jenner introduced matter from a sore on a dairymaid’s hand into the arm of a healthy eight-year-old, James Phipps. Six weeks later he tried hard to infect the lad with smallpox. Happily for young James and the rest of us, the inoculation worked, as it did in further trials with cowpox. 609 smallpox ‘This disease leaves the constitution in a state of perfect security from the infection of the smallpox,’ Jenner reported. In an early manifestation of peer review, the Royal Society of London refused to publish his manuscript. Gratuitously it added the caution, ‘He had better not promulgate such a wild idea if he valued his reputation.’ When Jenner issued a monograph at his own expense, the clerics joined the medics in denouncing him. Nevertheless the treatment plainly worked, and commended itself to the likes of the French and Spanish emperors and the US president. By 1807 a grateful British parliament had rewarded Jenner with £30,000, equivalent to about £1 million today. And in less than 200 years cowpox had wholly extinguished smallpox. I A biological weapon Or had it? Alongside the dairymaid’s blessing, there remained General Amherst’s curse. Nothing shows more graphically than smallpox how moral and political issues are magnified and dramatized by the power of science. The campaign against smallpox brought out the best in people. Thomas Jefferson personally saw to it that Jenner’s vaccination was demonstrated to Native Americans. And for the last big push, which occurred during the Cold War, humanity was united as never before as a single species with a common interest in eliminating smallpox from even the poorest and most remote parts of the world—and damn the cost. Yet smallpox also brought out the worst, in governments and their scientific servants. What was superficially a scholarly argument within the World Health Organization, about what should be done with laboratory stocks of smallpox virus after eradication was certified in 1980, concealed a deeper anxiety. New generations would grow up as immunologically naı ¨ ve in respect of smallpox as the Aztecs were. They would then be sitting ducks for smallpox used as a military or terrorist weapon. Internationally approved stock s of smallpox virus were reduced to those at the Centers for Disease Control and Prevention in Atlanta, and at the Ivanovsky Institute for Viral Preparations in Moscow. The case for destroying these, too, was that as long as they existed they could escape and cause an epidemic. A minor argument for keeping them was that they might be needed for future medical research. The main objection to their destruction was that no one knew for sure if the Atlanta and Moscow stocks were the only ones. The destruction of the smallpox virus was deferred repeatedly for want of consensus in the World Health Organization’s multinational executive board. Concern about a smallpox weapon was no paranoid fantasy. That became clear when the Soviet Union collapsed. Ken Alibek (Kanatjan Alibekov) had been 610 smallpox deputy chief of a Soviet weapons prog ramme called Biopreparat, and in 1992 he turned up in the USA as a defector with chilling information. One of his jobs had been to work out tactics to circumvent the agreed restriction of the smallpox stock to Moscow, and to evade the Biological and Toxin Weapons Convention of 1972, which limited research to defensive measures only. A high priority was to get international approval for moving the official stock from Moscow to a virology centre near Novosibirsk, called Vektor, which was secretly engaged in research on a smallpox weapon. To preserve all essential information against the day when the virus might have to be killed, molecular biologists embarked on a complete analysis of the genes of smallpox, and also of cowpox. The aim was then to modify the cowpox virus by genetic engineering, which could be done under the guise of vaccine research but really aimed at a virulent product. The Soviet Union was meanwhile culturing the old-fashioned stuff on a grand scale. ‘In the late 1980s and early 1990s, over 60,000 people were involved in the research, development, and production of biological weapons,’ Alibek reported. ‘Hundreds of tons of anthrax weapon formulation were stockpiled, along with dozens of tons of smallpox and plague.’ The risk of accidental releases was ever-present. Alibek told of anthrax escaping from a weapons facility in Sverdlovsk in 1979. In the cover-up, medical records of victims were destroyed and a peasant was arrested for allegedly supplying meat contaminated with anthrax. Western intelligence agencies had little inkling of the Soviet programme. Unlike nuclear weapons, disease agents need no large facilities visible to spy satellites for preparing the materials. Any vaccine factory can be converted into a weapons plant overnight. The delivery system can be as simple as Amherst’s contaminated blankets, or the mailed letters used in small-scale anthrax attacks on the US government in 2001. In 1992 the Russian leader Boris Yel’tsin officially halted all activity on biological weapons. Alibek noted that the smallpox stock was nevertheless moved to Vektor in 1994. Papers subsequently appearing in the open literature about modified cowpox viruses suggested to him that the weapons programme was on track. With the rise of international ter rorism, smallpox and other bioweapons seem apt for attacks on civilian populations aimed at killing as many people as possible. Several countries began stockpiling smallpox vaccine again and vaccinating key personnel. Alibek became president of Advanced Biosystems Inc. under contract to the US Defense Advanced Projects Agency, and was soon helping to run the Center for Biodefense at George Mason University. He said, 611 smallpox ‘We need to create a new generation of scientists who will be able to work in civilian biodefence.’ E For another military use of science, see Nuclear weapons. For more on the biomedical side, see Immune system. R adiocarbon dating was a nuclear chemist’s great gift to the archaeologists. Willard Libby at Chicago commended it to them in 1949, giving examples of objects where his dates were in line with ages known by other means. The idea was simple. Living things absorb radioactive carbon-14 from the air, but when they die, and become building wood or charcoal or leather, the radiocarbon content gradually diminishes over thousands of years, as the radioactive atoms decay. Measure what remains, and you can tell how old the objects are. This beautiful recipe was soon spoiled by absurdities, such as pharaohs who were dated as reigning after their known successors. The explanation came from a biophysicist, Hessel de Vries, at Groningen in 1958. The rate of production of radiocarbon in the atmosphere had varied over the centuries and millennia, he said, because of changes in the intensity of cosmic rays. These are energetic subatomic particles coming from the Galaxy, and they manufacture radiocarbon by interactions with nitrogen atoms in the air. For the discontented archaeologists the remedy came from long-lived trees, in particular the bristlecone pines of California’s White Mountains. Thanks to the work of Edmund Schulman and his successors at Arizona, the age of every ring of annual growth was known by counting, in a series of wood samples going back 8000 years. The nuclear chemist Hans Suess of UC San Diego looked to see how the tree rings’ radiocarbon dates compared with their counted ages. In 1967 he published a chart showing a remarkable series of wiggles, indicating significant changes in the radiocarbon production rate. When archaeolog ists used the bristlecone results to calibrate their dates, the effects were revolutionary. A cherished idea that civilization and technologies 612 solar wind diffused outwards from Sumeria and Egypt was confounded when the corrected radiocarbon dates showed that folk in Brittany were building large stone monuments 1500 years before the first rough-stone Egyptian pyramid was constr ucted. As Colin Renfrew at Southampton announced in 1973: ‘The whole diffusionist framework collapses, and with it the assumptions which sustained prehistoric archaeology for nearly a century.’ But why did the cosmic rays vary so much? Gradual changes in the Earth’s magnetic field explained the long-term trend, but not the Suess wiggles. To begin to answer the question, an equally revolutionary change was needed, in perceptions of the Earth’s relationship to the Sun. Here the big surprise was the discovery of the solar wind. I An escalator that repels cosmic rays The Earth’s magnetic field partly protects the atmosphere and surface from cosmic rays. In the equatorial zone, where it is most effective, only the most energetic cosmic-ray particles penetrate the shield. In the polar regions, the rays are funnelled towards the atmosphere by the field lines converging on the magnetic poles. The monitoring of cosmic rays worldwide therefore seemed an appropriate task for experts in terrestrial magnetism at the Carnegie Institution in Washington DC. Scott Forbush was given the job, and in 1935–36 he set up a worldwide network of recording instruments, initially in Maryland, Peru and New Zealand. ‘Study cosmic rays and see the world,’ a friend recalled about Forbush. ‘He car ried a battered leather briefcase for many years and took a quiet pride in the dozens of stubs from airlines, shops, and hotels that he allowed to accumulate on its handle, a kind of archaeological record of his travels.’ Working almost alone for two decades, Forbush made salient discoveries about cosmic-ray variations. He found cycles of 27 days, linked to the rotation of the Sun, and cycles of 11 years, following the sunspot cycles in which the count of dark spots on the visible face waxes and wanes. He detected bursts of cosmic- ray-like energetic particles emanating from solar flares. But otherwise high sunspot counts, denoting a stormy Sun, were associated with a big reduction in cosmic rays coming from the Galaxy. Forbush decreases are the name still given to sharp drop-offs in cosmic-ray intensities that can follow exceptional solar eruptions. These are also associated with magnetic storms on the Earth, which set compass needles wandering. The coincidence misled Forbush into an Earth-centred view of events. He thought that variations in the cosmic rays were due to changes in the magnetic environment of the Earth, when in fact both phenomena are caused by the Sun’s behaviour. 613 solar wind [...]... they would annihilate each other, as particles and antiparticles do, disappearing in a puff of gamma rays Bye-bye, atoms Proton decay would break a cherished elementary law of science, about the conservation of matter Salam’s daughter was warned by a schoolteacher not to mention such a heretical idea in her exams, whatever her famous father might say Professional physicists needed some persuading, too... magnetosphere, streaming away on the dark side The pressure of a mass ejection tweaking the tail can provoke a magnetic explosion there, which causes auroras The Earth can also lay a magnetic egg, if part of its tail breaks off as a blob that’s swept away on the solar wind Solar-wind particles sneak into the magnetosphere by this back door, when the magnetic fields of the Sun and Earth are suddenly joined... such a deep notion without any experimental input!’ Unless some anchor in real observations is found, scepticism about the superworld will start to grow A five-year search for sparticles at Fermilab near Chicago, begun in 199 6, concluded only that a gluino, if it exists at all, must be at least as heavy as an atom of lead That was beyond the capacity of Fermilab’s Tevatron accelerator to manufacture... explicable by Grand Unification Why matter is electrically neutral, for example If positive and negative charges were not exactly in balance, matter would blow up and stars and planets could not form The theory takes care of that, yet at the same time makes it possible for matter to be far from neutral in respect of antimatter If the proportions of matter and antimatter were as equal as the electric charges... Explaining solar flares By the end of the 20th century, space weather had entered official and academic usage as a unifying term for a wide range of research, extending from the visible 624 s pa c e w e at h e r surface of the Sun to the far planets and beyond An International Solar–Terrestrial Programme was in progress as a joint effort of the world’s space agencies, involving some 16 spacecraft and... by day,’ said Saku Tsuneta of the National Astronomical Observatory of Japan ‘Storms on the Sun are even more dramatic and complicated than those on the Earth, and Yohkoh’s chief achievement was to show that solar flares release huge magnetic energy stored in the atmosphere.’ Flares had been known since 18 59, when an amateur astronomer in England, Richard Carrington, first reported an exceptionally... electron beams of TV 620 s pa c e w e at h e r tubes, hit the upper air and make the atoms glow The kinetic art is a virtual image of plasma clouds, magnetized masses of electrons and charged atoms, which squirm and swirl in the Earth’s space environment Grand auroras are sometimes visible far beyond the normal auroral zone They occur when an exceptional blast of gas, which left the Sun a few days before,... his idea of variable magnetic fields pervading interplanetary space Then an important clue came from a completely different direction The tail of a comet always points directly away from the Sun, regardless of which way the comet is travelling The conventional explanation was that sunlight pushed the tail away Whilst that was fair enough, for the fine dust grains in the tail, Ludwig Biermann at Gottingen... a position 1.5 million kilometres out on the sunward side of the Earth, early in 199 6 Built in Europe, the Solar and Heliospheric Observatory was launched by NASA in a project of international cooperation Among a dozen sets of instruments on SOHO provided by multinational teams, several gave new views of the solar atmosphere at ultraviolet wavelengths SOHO generated remarkable movies of the solar atmosphere,... have direct evidence for the upward transfer of magnetic energy from the Sun’s surface towards the corona above.’ Later, Title and his colleagues looked in more detail at this mechanism of atmospheric heating by magnetic loops, using their small Trace satellite launched by NASA in 199 8 It gave ultraviolet images sharper and more frequent than SOHO’s, and showed an endless dance of magnetic loops, made . Health Organization in Geneva formally declared smallpox eradicated, after a 15-year programme in which vaccinators visited every last shantytown and nomadic tribe. This was arguably the greatest. liberate a quark in ordinary reactions between particles, you unavoidably create a new quark and an antiquark. One of them immediately replaces the extracted entity. The new antiquark handcuffs. what the theory says, anyway, but to set the quarks free experimentally required creating a new state of matter never seen before. I A spectacular excess of strangeness’ A multinational team of