Universe a grand tour of modern science Phần 6 potx

T he cheap cigars with which the young Alber t Einstein surrounded himself in a smoky haze were truly dreadful. If he gave you one, you ditched it surreptitiously in Bern’s Aare River. So when Einstein went home to his wife and son in the little flat on Kramgasse, after a diligent day as a technical officer (third class) at Switzerland’s patent office, he spent his evenings putting the greybeards of physics right, about the fundamentals of their subject. That was how he sought fame, fortune and a better cigar. In March 1905, a few days after his 26th birthday, he explained the photoelectric effect of particles of light, in a paper that would eventually win him a Nobel Prize. By May he had proved the reality of atoms and molecules in explaining why fine pollen grains dance about in water. He then pointed out previously unrecognized effects of high-speed travel, in his paper on the special theory of relativity, which he finished in June. In September he sent in a postscript saying ‘by the way, E ¼ mc 2 .’ Retrospectively Louis de Broglie in Paris called Einstein’s results that year, ‘blazing rockets which in the dark of the night suddenly cast a brief but powerf ul illumination over an immense unknown region.’ All four papers appeared in quick succession in Annalen der Physik, but the physics community was slow to react. The patent office promoted Einstein to technical officer (second class) and he continued there for another four years, before being appointed an associate professor at Zurich. Only then had he the time and space to think seriously about spacetime, gravity and the general theory of relativity, which would be his masterpiece. The much simpler idea of special relativity still comes as a nasty shock to students and non-scientists, long after the annus mirabilis of 1905. Schoolteachers persist in instilling pre-Einsteinian physics first, in the belief that it is simpler and more in keeping with common sense. That is despite repeated calls from experts for relativity to be learnt in junior schools. I Tampering with time In the 21st-century world of rockets, laser beams, atomic clocks, and dreams of flying to the stars, the ideas of special relativity should seem commonsensical. 373 Einstein’s Universe is democratic, in that anyone’s point of view is as good as anyone else’s. Despite the fact that stars, planets, people and atoms rush about in relation to one another, the behaviour of matter is unaffected by the motions. The laws of physics remain the same for everyone. The speed of light, 300,000 kilometres per second, figures in all physical, chemical and biological processes. For example the electric force that stitches the atoms of your body together is transmitted by unseen particles of light. The details were unknown to Einstein in 1905, but he was well aware that James Clerk Maxwell’s electromagnetic theory, already 40 years old, was so intimately linked with light that it predicted its speed. That speed must always be the same for you and for me, or one or other of our bodies would be wonky. Suppose you are piloting a fighter, and I’m a foot soldier. You fire a rocket straight ahead, and its speed is added to your plane’s speed. Say 1000 plus 1000 kilometres per hour, which makes 2000. I’d be pedantic to disagree about that. Now you shoot a laser beam. As far as you are concerned, it races ahead of your fighter at 300,000 kilometres a second, or else your speed of light would be wrong. But as far as I’m concerned, on the ground, the speed of your fighter can have no add-on effect. Whether the beam comes from you or from a stationary laser, it’s still going at 300,000 kilometres a second. Otherwise my speed of light would be wrong. When you know that your laser beam’s speed is added to your f ighter’s speed, and I know it’s not, how can we both be right? The answer is simple, though radical. Einstein realized that time runs at a different rate for each of us. When you say the laser beam is rushing ahead at the speed of light, relative to your plane, I know that you must be measuring light speed with a clock that’s running at a slow rate compared with my clock. The difference exactly compensates for the speed of the plane. Einstein made a choice between two conflicting common-sense ideas. One is that matter behaves the same way no matter how it is moving, and the other is that time should progress at the same rate everywhere. There was no contest, as he saw it. His verdict in special relativity was that it was better to tamper with time than with the laws of physics. The mathematics is not difficult. Two bike riders are going down a road, side by side, and one tosses a water bottle to the other. As far as the riders are concerned, the bottle travels only the short distance that separates them. But a watcher standing beside the road will see it go along a slanting track. That’s because the bikes move forward a certain distance between the moments when the bottle leaves the thrower and when it arrives in the catcher’s hand. The watcher thinks the bottle travels farther and faster than the riders think. 374 high-speed travel If the bottle represents light, that’s a more serious matter, because there must be no contradiction between the watcher’s judgement of the speed and the riders’. It turns out that a key factor, in reckoning how slow the riders’ watches must run to compensate, is the length of the slanting path seen by the watcher. And that you get from the theorem generally ascribed to Pythagoras of Samos. In the 1958 movie Merry Andrew, Danny Kaye summed it up in song: Old Einstein said it, when he was getting nowhere. Give him credit, he was heard to declare, Eureka! T he square of the hypotenuse of a right triangle Is equal to the sum of the squares of the two adjacent sides. Cognoscenti of mathematical lyrics preferred the casting for the movie proposed in Tom Lehrer’s ‘Lobachevsky’ (1953) to be called The Eternal Triangle.The hypotenuse would be played by a sex kitten—Ingrid Bergman in an early version of the song, Brigitte Bardot later. Whether computed with an American, Swedish or French accent, it’s the Pythagorean hypotenuse you divide by, when correcting the clock rate in a vehicle that’s moving relative to you. The slowing of time in a moving object has other implications. One concerns its mass. If you try to speed it up more, using the thrust of a space traveller’s rocket motor or the electric force in a particle accelerator, the object responds more and more sluggishly, as judged by an onlooker. The rocket or particle responds exactly as usual to the applied force by adding so many metres per second to its speed, every second. But its seconds are longer than the onlooker’s, so the acceleration seems to the onlooker to be reduced. The fast-moving object appears to have acquired more inertia, or mass. When the object is travelling close to the speed of light, its apparent mass grows enormously. It can’t accelerate past the speed of light, as judged by the onlooker. The increase in mass during high-speed travel is therefore like a tacho on a truck—a speed restrictor that keeps the traffic of Einstein’s Universe orderly. I A round trip for atomic clocks Imagine people making a high-speed space voyage, out from the Earth and back again. Although the slow running of clocks stretches time for them, as judged by watchers at home, the travellers have no unusual feelings. Their wristwatches and pulse-rate seem normal. And although the watchers may reckon that the travellers have put on a grievous amount of weight, in the spaceship they feel as spry as ever. 375 high-speed travel But what is the upshot when the travellers return? Will the slow running of their time, as judged from the Earth, leave them younger than if they had stayed at home? Einstein’s own intuition was that the stretching of time should have a lasting effect. ‘One could imagine,’ he wrote, ‘that the organism, after an arbitrarily lengthy flight, could be returned to its original spot in a scarcely altered condition, while corresponding organisms which had remained in their original positions had long since given way to new generations.’ Other theorists, most vociferously the British astrophysicist Herbert Dingle, thought that the idea was nonsensical. This clock paradox, as they called it, violated the democratic principle of relativity, that everyone’s point of view was equally valid. The space travellers could consider that they were at rest, the critics said, while the Earth rushed off into the distance. They would judge the Earth’s clocks to be running slow compared with those on the spaceship. When they returned home there would be an automatic reconciliation and the clocks would be found to agree. Reasoned argument failed to settle the issue to everyone’s satisfaction. This is not as unusual in physics as you might think. For example the discoverer of the electron, J.J. Thomson, resisted for many years the idea that it was really a particle of matter, even though his own maths said it was. There is often a grey area where no one is quite sure whether the mathematical description of a physical process refers to actual entities and events or is just a convenient fiction that gives correct answers. For more than 60 years physicists were divided about the reality and persistence of the time-stretching. Entirely rational arguments were advanced on both sides. They used both special relativity and the more complicated general relativity, which introduced the possibility that acceleration could compromise the democratic principle. Indeed some neutral onlookers suspected that there were too many ways of looking at the problem for any one of them to provide a knockdown argument. The matter was not decided until atomic clocks became accurate enough for an experimental test in aircraft. ‘I don’t trust these professors who get up and scribble in front of blackboards, claiming they understand it all,’ said Richard Keating of the US Naval Observatory. ‘I’ve made too many measurements where they don’t come up with the numbers they say.’ In that abrasive mood it is worth giving a few details of an experiment that many people have not taken seriously enough. On the Internet you’ll find hundreds of scribblers who still challenge Einstein’s monkeying with time, as if the matter had not been settled in 1971. That was when Keating and his colleague Joe Hafele took a set of four caesium- beam atomic clocks twice around the world on passenger aircraft. First they flew from west to east, and then from east to west. When returned to the lab, 376 high-speed travel the clocks were permanently out of step with similar clocks that had stayed there. Einstein’s intuition had been correct. Two complications affected the numbers in the experiment. The eastbound aircraft travelled faster than the ground, as you would expect, but the westbound aircraft went slower. That was because it was going against the direction in which the Earth rotates around its axis. At mid-latitudes the speed of the surface rotation is comparable with the speed of a jet airliner. So the westbound airborne clocks should run faster than those on the ground. The other complication was a quite different Einsteinian effect. In accordance with his general relativity, the airborne clocks should outpace those on the ground. That was because gravity is slightly weaker at high altitude. So the westbound clocks had an added reason to run fast. They gained altogether 273 billionths of a second. If any airline passengers or crew had made the whole westabout circumnavigation, they would have aged by that much in comparison with their relatives on the ground. In the other direction, the slowing of the airborne clocks because of motion was sufficient to override the quickening due to weak gravity. The eastbound clocks ran slow by 59 billionths of a second, so round-trip passengers would be more youthful than their relatives to that extent. The numbers were in good agreement with theoretical predictions. The details show you that the experiment was carefully done, but the cr ucial point was really far, far simpler. When the clocks came home, there was no catch-up to bring them back into agreement with those left in the lab, as expected by the dissenters. The tampering with time in relativity is a real and lasting effect. As Hafele and Keating reported, ‘These results provide an unambiguous empirical resolution of the famous clock paradox.’ I The Methuselah Effect If you want to voyage into the future, and check up on your descendants a millennium from now, a few millionths of a second gained by eastabout air travel won’t do much for you. Even when star-trekking astronauts eventually achieve ten per cent of the speed of light, their clocks will lag by only 1 day in 200, compared with clocks on the Earth. Methuselah repor tedly survived for 969 years. For the terrestrial calendar to match that, while you live out your three score and ten in a spaceship, Mistress Hypotenuse says that you’ll have to move at 99.74 per cent of light speed. Time-stretching of such magnitude was verified in an experiment reported in 1977. The muon is a heavy electron that spontaneously breaks up after about 2 millionths of a second, producing an ordinary electron. In a muon storage ring at CERN in Geneva, Emilio Picasso and his colleagues circulated the particles at 377 high-speed travel 99.94 per cent of the speed of light and recorded their demise with electron detectors. The high-speed travel prolonged the muons’ life nearly 30-fold. The Methuselah Effect in muons has physical consequences on the Earth. Cosmic rays coming from the stars create a continuous rain of fast-moving muons high in the Earth’s atmosphere. They are better able to penetrate the air than electrons are, but they would expire before they had descended more than a few hundred metres if their lives were not stretched by their high speeds. In practice the muons can reach the Earth’s surface, even penetrating into the rocks. You can give Einstein the credit or the blame for the important part that muons play in the cosmic radiation that contributes to genetic mutations in living creatures, and affects the weather at low altitudes. If you want to exploit special relativity to keep you alive for as long as possible, the most comfortable way to travel through the Universe will be to accelerate steadily at 1g—the rate at which objects fall under gravity at the Earth’s surface. Then you will have no problems with weightlessness, and you can in theory make amazing journeys during a human lifetime. This is because the persistent acceleration will take you to within a whisker of the speed of light. Your body-clock will come almost to a standstill compared with the passage of time on Earth and on passing stars. Through your window you will see stars rushing towards you, and not only because of the direct effect of your motion towards them. The apparent distance that you have to go keeps shrinking, as another effect of relativity at high speeds. In a 1g spaceship, you can for example set out at age 20, and travel right out of our Galaxy to the Andromeda Galaxy, which is 2 million light-years away. By star ting in good time to slow down (still at 1g) you can land on a planet in that galaxy and celebrate your 50th birthday there. Have a look around before setting off for home, and you can still be back for your 80th birthday. But who knows what state you’ll find the Earth to be in, millions of years from now? If stopping is not an objective, nor returning home, you can traverse the entire known Universe during a human lifetime, in your 1g spaceship. Never mind that it is technologically far-fetched. The fact that Uncle Albert’s theory says it’s permissible by the laws of physics should make the Universe feel a little cosier for us all. I ‘A sure bet’ Astronomers have verified Einstein’s intuition that the speed of light is unaffected by the speed of the source. For example, changes in the wavelength of light often tell them that one star is revolving around another. Sometimes it is swinging towards us, and sometimes receding from us on the other side of its companion. For a pulsating star, the time between pulses varies too. 378 high-speed travel Suppose Einstein was wrong, and the speed of light is greater when the star is approaching, and slower when it is receding. Then the arrival times of pulses from a pulsating star orbiting a stellar companion will vary in an irregular manner. That doesn’t happen. X-rays are a form of light, and in 1977 Kenneth Brecher of the Massachusetts Institute of Technology applied this reasoning to an X-ray star in a nearby galaxy, the Small Magellanic Cloud. There, the X-ray source SMC X-1 is orbiting at 300 kilometres per second around its companion, yet there is no noticeable funny business in the arrival of the X-rays. So the proposition about the invariance of the speed of light from a moving source is correct to at least one part in a billion. By 2000 Brecher was at Boston University, and using observations of bursts of gamma rays in the sky to make the proposition even more secure. The greater the distance of an astronomical source, the more time there would be for light pulses travelling at different speeds to separate before they reach our telescopes. The gamma bursters are billions of light-years away. In all credible theories of what these objects may be, pieces of them are moving relative to one another other at 30,000 kilometres per second or more. Yet some observed gamma-ray bursts last for only a thousandth of a second. If there were the slightest effect of the motions of the sources on the light speed, a burst could not remain so brief, after billions of years of space travel. With this reasoning Brecher reduced any possible error in Einstein’s proposition to less than one part in 100 billion billion. He said, ‘The constancy of the speed of light is as close to a sure bet as science has ever found.’ E For E ¼ mc 2 as the postscript to special relativity, see Energy and mass. For general relativity, see Gravity. For other tricks with clocks, see Time machines. 379 high-speed travel A mong the many poignant stories of discoveries shunned, Barbara McClintock’s had a moderately happy ending in 1983, when she won a Nobel Prize at the age of 81. But that followed decades of literally tearful frustration. Her work, done somewhat reclusively at the Cold Spring Harbor Laboratory, New York, was so ignored that she hesitated even to publish her latest results. She uncovered a new world of hereditary phenomena unknown to geneticists and evolutionists, simply by careful study of discoloured maize. But that was McClintock’s problem. Most biologists who were aware of her work thought it concerned only a peculiarity in a cultivated crop. Breeders and farmers of maize are familiar with an instability that results in patches of differently coloured kernels appearing on the cob, in various shades of brown. In research begun in the 1940s, McClintock traced the processes involved. She found genes jumping about. They can change their positions within the chromosomes in which the maize genes are packaged, or vault from one chromosome to another. Her mobile genetic elements, or transposons, are now textbook stuff. ‘We are all, unfortunately, dependent on recognition,’ wrote a close friend, Howard Green of the Harvard Medical School. ‘We grow with it and suffer without it. When transposons were demonstrated in bacteria, yeast and other organisms, Barbara rose to a stratospheric level in the general esteem of the scientific world and honours were showered upon her. But she could hardly bear them.’ McClintock’s discoloured maize was only the thin end of a very large wedge inserted into pre-existing ideas about heredity. Jumping genes in trypanosomes, the parasites that cause sleeping sickness, showed internal rearrangements like those in maize. By changing the surface molecules of the trypanosomes, the jumping genes help them to evade the defensive antibodies in previously infected animals. And genes controlling cell growth in animals, jumping from one chromosome to another, turned out to be a cause of cancer. The jumping genes also gave a brand-new slant on how genes form and change. Alas, the young fogies who ignored McClintock’s discoveries had hidebound 380 ideas about genes and their behaviour. Only in the 21st century is it glaringly obvious that jumping genes play a major part in evolution. McClintock died in 1992. What a pity she didn’t live just a few years more to see the reading of genomes—complete sets of genes of bacteria, plants and animals. These revealed jumping genes on a colossal scale. In the weed arabidopsis, for example, the genome analysts identified 4300 mobile elements accounting for at least ten per cent of the DNA. Most of the genes in the regions of genetic material rich in transposons are inactive. Normally the unwanted transposons are marked with chemical attachments— simple methyl groups (CH 3 )—that silence them. At Japan’s National Institute of Genetics, Tetsuji Kakutani and his colleagues experimented with a form of arabidopsis in which the mutation of a single gene impaired this methylation. Other genes, normally silenced, were de-repressed, so that there were knock-on effects, and these proved to be inheritable. The mutation also destabilized the weed’s genetic structure, by leaving some transposons free to jump. In 2001 the team reported remarkable consequences. ‘It was quite dramatic,’ Kakutani said. ‘We had a dwarf form of the weed, itself produced by a transposon jump in a mutant with reduced methylation. Then its descendants showed mosaic structure of shape as jumping continued. For example, within a single plant, one stem grew taller with normal leaves, while other parts remained dwarf. The changes were all inheritable, so we were watching with our own eyes a surprising natural mechanism available for evolution.’ I Crossing a valley of death By then the world’s chief factory for accelerated evolution was in Chicago, in the Howard Hughes Medical Institute on East 58th Street. In the course of a few years, 1998–2002, Susan Lindquist reported some very odd-looking flies, yeasts and weeds. In these cases jumping genes were not involved, but like Kakutani’s weeds the products gave a stunning new insight into how species evolve. They were hopeful monsters. That term came into biology in 1933, coined by Richard Goldschmidt of the Kaiser-Wilhelm-Institut fu ¨ r Biologie in Berlin-Dahlem. Technically, a monster is a creature with structural deformities. By a hopeful monster Goldschmidt meant a fairly well coordinated new organism, quite different from its colleagues, appearing in the course of a major evolutionary change. For him, such a hypothetical creature was needed to explain jumps in evolution. Darwin’s natural selection operates by favouring the individuals within a species best adapted to their way of life. It weeds out harmful mutations in a very conservative way. Suppose now you want a feathered dinosaur to evolve into a 381 hopeful monsters flying bird. A great many changes are required—to limbs, muscles and brain, just for starters. If you do the revamp slowly, gene by gene, as required in the then-emergent neo-Darwinist theory, you will have creatures that are neither good dinosaurs nor good birds. They will be selected against, to perish in a valley of death long before they reach the sanctuary of Bird Mountain. Goldschmidt wanted hopef ul monsters that would make such transitions more quickly. In Chicago, six decades later, Lindquist and her team made fruit flies that had deformed wings or eyes. At first sight you’d think that they were just another batch of the Drosophila melanogaster monsters, produced routinely by genetic mutations, which have populated genetics labs for many decades. But in Lindquist’s flies the output of several genes changed at the same time, making them hopeful monsters in Goldschmidt’s sense. I Not just a dirty word To see such experiments in historical context, go back two centuries to Paris during the Napoleonic Wars. In 1809, Jean-Baptiste de Lamarck of the Muse ´ um National d’Histoire Naturelle gave the earliest coherent account of evolution. ‘He first did the eminent service,’ Darwin said of him, ‘of arousing attention to the probability of all change in the organic, as well as in the inorganic world, being the result of law, and not of miraculous interposition.’ Lamarck also invented the term biologie and classified the invertebrate animals. But history has not been kind to him. ‘Lamarckian’ became a dirty word, for referring to a supposedly ludicrous theory of how evolution proceeds. Lamarck’s giraffe famously acquired its long neck by striving to nibble leaves high in the trees that other animals could not reach. The exercise affected heredity in its offspring. Generation by generation the neck got longer. It was a very slow process, Lamarck thought. But seen in retrospect there was a feature of his theory that would chime with the idea of hopeful monsters and the rapid evolution they might make possible. This was the possibility that several or many individuals might acquire the same alterations simultaneously, thereby greatly improving the chances of finding a similar mate and reproducing, to carry the changes forward to new generations. Lamarck’s belief that characteristics acquired by organisms during their lives could be inherited was at odds with the idea of natural selection advanced by Darwin in The Origin of Species (1859). In this theory, an animal that by chance happens to have a longer neck than others in the herd may have an advantage when food is scarce. It is therefore more likely to leave surviving offspring, also with long necks. Hence Darwin’s giraffe. 382 hopeful monsters [...]... literally boiling off Iceland’s south coast, and within 24 hours a brand-new volcanic appendage had appeared, a small island now called Surtsey Ten years later, the citizens of Heimaey barely saved their coastal town from erasure by the nearby Eldfell volcano They hosed the lava to make a dam of frozen rock An eruption of the Gjalp volcano ¨ underneath the Vatnajokull glacier in 1995 caused spectacular... Peruvian side of Titicaca In other settings, on the coastal plains of Colombia and Ecuador, and in the old Maya heartlands of Central America, farming techniques adapted to lowland conditions were being rediscovered by archaeologists and implemented in local trials After half a millennium of colonial and post-colonial scorn for the retarded ways of the Native Americans, the tables were turned The moral of. .. ditches Starting in 1984, in collaboration with Rivera, Alan Kolata from the University of Chicago led excavations that revealed how the raised fields looked and functioned before they fell into disrepair The engineering was meticulous The Tiwanakans lined a dug-out area with stones and clay, to make it proof against flooding from the brackish water table below Next, a layer of gravel and sand provided... terms I Mapping plate movements Earth scientists fell into the habit of blaming all volcanoes away from plate margins on mantle plumes, under continents as well as the oceans Morgan had suggested the hotspot of Yellowstone Park in Wyoming as a plume candidate, and soon Ethiopia, Kenya, Germany and many other mid-continental places were added Up for consideration was almost anywhere, not on a plate 390... Incas who came to power later, nor the Spanish colonial settlers who displaced the Incas, could match the agrarian productivity of the Tiwanakans When international agricultural experts arrived, in the 1950s and after, to counsel the Bolivians on modern techniques, they had nothing to offer for that part of the Altiplano that was not hopelessly expensive For almost 1000 years the land was wasted, because... h u m a n e c o lo gy north-western USA and in Finland, that wasn’t what the world heard about The word was that the Brazilians were wiping out the Amazon rain forest There satellites did indeed show large clearings near the roads and rivers, but also huge areas of scarcely affected forest Careful measurements by US scientists using Landsat images showed that the rate of deforestation in the Amazon... result of the plate boundary of the Mid-Atlantic Ridge drifting over a fixed mantle plume On the other side of the world, Hawaiian islanders tell how the volcano goddess Pele carried her magic spade south-eastwards across the sea, making one island after another Finally she settled in Kilauea, the currently active volcano on the south-east corner of the big island of Hawaii That Pele still has itchy... observer of this fiasco was Paul Cox, from Brigham Young University in Utah, who had lived and worked in Samoa for some years and spoke the language As an ethnobotanist, he was accustomed to learning from the Samoans about the precious plants of the rain forest, and their medicinal properties When he found one that promised to ameliorate AIDS, he saw to it that a 20 per cent royalty on any profits should... research in Nigeria and Cameroon, ‘by looking at how we can save the human population in order to ultimately save the wild species in the region.’ I Sustainable hopes? On the international stage, at the start of the 21st century, sustainability is the watchword How can humanity as a whole, with a growing population and hopes of higher standards of living, avoid exhausting its resources and damaging... is shown by activity already occurring offshore, near Kilauea Geology chimes with the folklore Starting with former islands to the far northwest, most of which are now eroded to submerged seamounts, the members of the Hawaiian chain have punched their ways to the surface one after another Huge cones of basaltic lava have arisen from the deep ocean floor at intervals of about a million years On the youngest . basaltic lava have arisen from the deep ocean floor at intervals of about a million years. On the youngest island, Mauna Kea and Mauna Loa stand 4200 metres above sea level and 10,000 metres above. boiling off Iceland’s south coast, and within 24 hours a brand-new volcanic appendage had appeared, a small island now called Surtsey. Ten years later, the citizens of Heimaey barely saved their coastal. doesn’t happen. X-rays are a form of light, and in 1977 Kenneth Brecher of the Massachusetts Institute of Technology applied this reasoning to an X-ray star in a nearby galaxy, the Small Magellanic