Innholdsfortegnelse for EG15 i New Scientist - The Essential Guides

IF YOU fall off the top of a cliff, how does the ground below “know” you are up there for it to attract you? It is a question that has taxed many illustrious minds ever since Isaac Newton’s universal law of gravitation first allowed such apparently instantaneous “action at a distance”. Newton was among them: he described it in a letter as “so great an Absurdity that I believe no Man who has in philosophical Matters a competent Faculty of thinking can ever fall into it”. Today, we ascribe such absurdities to fields. Earth’s gravitational field, for example, extends out into space in all directions, tugging at smaller objects like the moon or people who get too close to large drops. Earth, too, is under the spell of the sun’s…

WE GO to incredible lengths to gather electrons. We generate them in vast power stations, string cables across the countryside to bear them to us and install sockets in the walls of every room to zap them into our devices. Our dependence on them makes it a shade embarrassing that we don’t fully grasp what they are. It was 1897 when J. J. Thompson observed rays that would bend under the influence of an electric field: the charged particles that orbit atomic nuclei that we now call electrons. By the mid-1930s, we had found the other components of atoms too: the proton and the neutron. But just as things began to look tidy, confusion descended again. In 1936, a pair of physicists in California who were studying radiation from deep…

NEUTRINOS are notoriously hard to pin down. They have no charge, almost no mass and can pass through matter by the millions without leaving a trace. The first inkling we had that they were out there came in 1930, when physicist Wolfgang Pauli was struggling to make sense of the decay of certain radioactive nuclei. When an atomic nucleus undergoes beta decay, it morphs into a daughter nucleus, emitting an electron in the process. But the two decay products went in directions that seemed to violate the cast-iron law of conservation of momentum – suggesting some third particle was needed to make sense of the results. The tiny, chargeless particle Pauli dreamed up was subsequently called the neutrino – “the little neutral one” – and was spotted in the wild…

THE most basic definition of an antimatter particle is that it is the same as a matter particle, except that it has the opposite charge. So the familiar electron, for example, with a negative charge of -1, has an antimatter equivalent called a positron that has a charge of +1. Similarly, an up quark (charge +2/3) is partnered by an up antiquark (charge -2/3). The same goes for composite particles made up of quarks: they, too, have their exact mirror equivalent. For the proton (quark composition: up-up-down; charge 2/3 + 2/3 + (-1/3) = 1), there is the antiproton (quark composition: anti-up-anti-up-anti-down; charge (-2/3) + (-2/3) + 1/3 = -1). So far, so simple. But a complicating factor is that “charge” doesn’t just mean the familiar, everyday electric charge. Three…

THE standard model of particle physics is underpinned by the quantum field theories that Paul Dirac and many others developed. It depicts empty space as a roiling quantum vacuum of particles and antiparticles that pop up as pairs, and confidently predicts that the big bang created equal quantities of matter and antimatter. They would have indulged in cyclical orgies of annihilation and recreation until the cooling, expanding universe could no longer supply enough energy for this. At that point… not a lot would have happened. The last matter-antimatter pairs would have annihilated, leaving the cosmos suffused with nothing but a lot of light and energy. The material universe of stars and galaxies and planets would have failed to materialise. “The fact that we are a world completely dominated by matter…

Few advances in fundamental physics captured the imagination like the discovery of the Higgs boson in 2012. It is the particle that gives all other fundamental particles their mass, and its existence was predicted in 1964 as part of efforts to find a theory that would unify electromagnetism and the weak nuclear force. In the end, the Higgs boson was the very last particle predicted by the standard model to be discovered. The half-century-long quest to find it, including the construction of the largest ever particle accelerator, CERN’s Large Hadron Collider, accounts for part of its mystique. But in the decade since the Higgs was discovered, it has presented particle physicists with another, profound problem: it works exactly as they predicted.…

IN ITS most simplified form, the standard model comprises an equation with four terms. The first describes the three forces within the model: electromagnetism and the strong and weak nuclear forces. The second sketches out the elementary particles and how the forces act on them. The two final terms are only just being written now. They largely tell the story of the Higgs boson. The Higgs is connected to many of the most troublesome aspects of the standard model. It is the linchpin for the ramshackle arrangement of particle masses, varying according to how strongly the Higgs couples to them. Electrons, for instance, are far lighter than their sister particles called muons, which are far lighter than their siblings called tau particles, and no one knows why. “It’s so chaotic,”…

THE discovery of dark energy came from one of the most unexpected results in the history of astronomy: in the late 1990s, two groups studying far-off supernovae discovered that these explosions of dying, overmassive stars were consistently fainter than expected. They concluded that the intervening space through which the supernovae’s light had travelled to get to us had stretched more than expected, making them further away than supposed – and so less bright. Dark energy is the name for whatever is causing this accelerating expansion. It dominates the cosmos, making up, by the latest reckoning, some 68 per cent of everything there is. But what is it? There, physicists are stumped, even more so than with dark matter. At least we know dark matter gravitates. The effect of dark energy…

ONE of the earliest attempts at unifying the forces of nature was made in the 1920s, when physicist Theodor Kaluza melded Albert Einstein’s gravitational theory with the electromagnetic theory of James Clerk Maxwell. The universe we live in appears to have four dimensions. Space has three – right-left, forwards-backwards and up-down – and the fourth is time. Kaluza rewrote Einstein’s theory as if there were five space-time dimensions. This gives the gravitational field some extra components that he thought could be interpreted as Maxwell’s electromagnetic field. Amazingly, he showed that these extra components precisely matched Maxwell’s equations. Electromagnetism comes for free if you are willing to buy a fifth dimension for gravity. Why can’t we see a fifth dimension? In 1926, physicist Oskar Klein came up with an answer. He…

Amalie “Emmy” Noether was born in the small German town of Erlangen, near Nuremberg, in 1882. Despite the fact that her father, Max Noether, was a professor at the University of Erlangen, she was initially forbidden from enrolling there because of her gender. Such discrimination dogged Noether’s career. Although she eventually gained both an undergraduate degree and a PhD, no university would hire her for a permanent faculty position. She eventually became one of the world’s foremost experts in the fields of abstract algebra, algebraic topology and the mathematics of symmetry, working at the University of Erlangen and subsequently the University of Göttingen. But for a decade, she was without appointment, pay or formal title, despite the championing of her work by many of the most prominent mathematicians of the…

GOVERNING THEORY: Quantum electrodynamics (QED) MEDIATOR: Photon (predicted by Albert Einstein in 1905) MAXIMUM RANGE: Infinite When asking what electromagnetism does, it is perhaps easier first to say what it doesn’t do. It doesn’t keep our feet on the ground, Earth swinging around the sun or the stars and galaxies in the universe moving: this is the domain of gravity. It doesn’t bind particles in the atomic nucleus, or determine their decay: the strong and weak nuclear forces do that. But pretty much everything else on scales between those two depends on electromagnetism. It was James Clerk Maxwell who, in the 1860s, showed that electricity and magnetism are in fact two aspects of one unified phenomenon: moving electric currents cause magnetic fields, and magnetic fields induce electric currents to flow.…

GOVERNING THEORY: Electroweak theory (unified theory with quantum electrodynamics, the theory of electromagnetism, at high energies) MEDIATOR: W and Z bosons (predicted in 1968, discovered in 1983) TYPICAL RANGE: 10-18 metres Of the four known fundamental forces, the weak nuclear force has the least obvious purpose. Its effects were first discovered at the turn of the 20th century, in the place where it is most obviously at work: in radioactive beta decay. In the most common form of this decay, beta-minus decay, a neutron decays into a proton, also spitting out a negatively charged electron to conserve electric charge; beta-plus decay does the reverse and turns protons into neutrons. This amounts to an ability unique to the weak force to change the “flavour” of the quarks that make up protons…

GOVERNING THEORY: Quantum chromodynamics (QCD) MEDIATOR: Gluons (predicted in 1962, discovered in 1979) TYPICAL RANGE: 10-15 metres Question: when is a strong force not a strong force? Answer: when it is anywhere outside the atomic nucleus. Because the strong force holds together quarks, the fundamental particles that make up the protons and neutrons of the atomic nucleus, and further holds together protons and neutrons to form atomic nuclei, it is responsible for the underlying stability of matter. Its huge power is also what is released in the process of nuclear fusion in the sun, or nuclear fission in a nuclear bomb. On subatomic scales of about 1 femtometre, or 10−15m, it is by far the strongest of the four forces, 137 times stronger than electromagnetism, and a million times stronger…

Stories of the eccentricities of Paul Dirac (1902 to 1984), the British physicist whose eponymous equation predicted the existence of antimatter, abound. Dirac was notoriously taciturn. When he first visited the institute led by pioneer of quantum theory Niels Bohr in Copenhagen in the 1930s, his reported utterances consisted almost entirely of three phrases: “Yes”, “No” and “I don’t mind”. Later, he became more flexible. When astrophysicist Subrahmanyan Chandrasekhar expounded his views, Dirac repeatedly interjected with “Yes”, but explained: “When I say ‘yes’, it does not mean that I agree; it means only that you should go on.” In 1929, Dirac sailed from the US to Japan with Werner Heisenberg. During the trip, Heisenberg spent the evenings dancing while Dirac looked on, puzzled. Eventually, Dirac asked his friend why he…

ETTORE MAJORANA had a talent for enigma. The mercurial Italian’s sudden disappearance, somewhere en route from Palermo to Naples in the spring of 1938, still excites lively discussion. The particles that bear his name are no less enigmatic. Their origin lies in a seemingly innocuous modification Majorana made to Paul Dirac’s equation that established the existence of antimatter in 1928. In Dirac’s original formulation, only electrically charged particles had antiparticles. Majorana’s tweak produced antiparticles for chargeless particles, too. Indistinguishable even by their charge, such a particle and its antiparticle would be absolutely identical. In fact, they would be one particle embodying all the qualities of both simultaneously. The idea sounds faintly absurd – but it can be tested. “If a particle is its own antiparticle, then if two of them…

WHAT happens if you break matter up into smaller and smaller pieces? Eventually, you get the component molecules or atoms. But these can be further broken down into electrons and atomic nuclei. The nuclei can then be torn apart to reveal their constituent protons and neutrons. Inside these, there are quarks. At this point, you have reached the level we regard as fundamental within the standard model. Whatever material you start with, at some point, you end up with a bunch of quarks and a bunch of particles like electrons. That’s it. Matter gets no smaller than this. This neat particle pattern fits the experimental facts, but hides a perplexing problem. All matter particles have a property called mass – a resistance to being moved around. This mass varies by…

TO MOST of us, the mass of an eyelash seems like just about nothing. But to a Higgs boson, it might as well weigh a tonne. If the mass of the Higgs were as large as an eyelash, the world would look very different. The electrons buzzing inside a computer’s circuits would be as weighty as the dust coating the top of it. If the dust bulked up on the same scale, each speck would have roughly the mass of a well-fed elephant. This might seem like idle and rather surreal picture painting, were it not for the fact that the standard model suggests the Higgs boson should probably have about the mass of an eyelash. Under the rules of quantum field theory, it can temporarily shape-shift into all sorts…

IT WAS around the turn of the 20th century that we saw the first glimpses of something beyond the atom. In 1897, physicist J. J. Thomson was investigating streams of particles given off by metal electrodes placed under high voltage in a vacuum. These particles turned out to be much smaller than atoms and, unlike neutral atoms, negatively charged. The discovery of these “electrons” put paid to the idea that the atom was uniform and indivisible. To maintain the atom’s overall electrical neutrality, Thomson suggested that electrons were embedded inside it like plums in a “pudding” of positive charge. By 1908, Ernest Rutherford, working with his assistant Hans Geiger at the University of Manchester, UK, had revealed a different picture. When fired from a radioactive source, positively charged “alpha particles”…

1898 PHYSICIST ARTHUR SCHUSTER COINS THE TERM “ANTIMATTER” IN TWO WHIMSICAL LETTERS TO NATURE SPECULATING ABOUT NEGATIVE MATTER 1928 PAUL DIRAC’S EQUATION DESCRIBING THE ELECTRON INDICATES THE EXISTENCE OF A POSITIVELY CHARGED ANTIMATTER ELECTRON: THE POSITRON 1932 CARL ANDERSON DISCOVERS THE POSITRON IN COSMIC RAYS 1964 DISCOVERY OF CP VIOLATION, AN ASYMMETRY IN PROCESSES PRODUCING MATTER AND ANTIMATTER, IN PROCESSES INVOLVING STRANGE QUARKS 1982 THE LOW-ENERGY ANTI PROTON RING, LEAR, COMES INTO OPERATION AT CERN WITH THE AIM OF MANUFACTURING ANTIHYDROGEN 1995 LEAR MAKES THE FIRST ATOMS OF ANTIHYDROGEN–BUT THEY ARE TRAVELLING TOO FAST TO STUDY 2000 CERN’S ANTIMATTER FACTORY STARTS UP, USING LEAR’S SUCCESSOR, THE ANTI PROTON DECELERATOR 2001 DISCOVERY OF CP VIOLATION IN PROCESSES INVOLVING BOTTOM QUARKS 2008 THE LARGE HADRON COLLIDER STARTS UP, WITH THE DEDICATED LHCB EXPERIMENT…

WHEN it comes to the question of whether antimatter falls downwards under the influence of gravity, as matter does, or asserts its own mirror identity by falling upwards, there are strong suppositions. “A huge majority of theoretical physicists, perhaps too huge to be right, believes antimatter falls the same way as matter,” says CERN theorist Dragan Hajduković. If it turns out that it instead falls up, everything is to play for. “It would really turn everything on its head from the instant of the big bang,” says Jeffrey Hangst at CERN’s ALPHA experiment. For a start, it means that anyone aiming to explain matter’s dominance in our universe through phenomena such as CP or CPT violation might be chasing shadows. If matter and antimatter fall in opposite directions, they probably…

AT 27 kilometres long, the Large Hadron Collider (LHC) is the largest machine in the world. Its most distinctive feature, though, is its temperature. At 1.9 kelvin – a smidgen above absolute zero – the LHC is the coldest ring in the universe, unless an alien civilisation has built one that is colder. Were it not for this searing cold, the LHC might have suffered the same fate as the Superconducting Super Collider (SSC), which was on its way to becoming the most powerful accelerator in the world before the US government canned it in 1993. The SSC’s partially completed 87-kilometre tunnel, near Waxahachie, Texas, now lies derelict – killed by a ballooning budget and a deficit of innovation. Keen to avoid a similar debacle, CERN, the European particle physics…

WE CAN’T weigh the sun or a planet directly. Instead, we determine its mass by measuring how its gravitational pull influences the motion of objects around it. In the same way, it should be possible to measure the mass of a galaxy, or even a cluster of galaxies, by observing how fast stars or other objects move around it. In 1933, astronomer Fritz Zwicky, working at the California Institute of Technology in Pasadena, applied this principle to the motion of galaxies that make up the Coma cluster, a group of over 1000 galaxies some 300 million light years from us. He found that the individual galaxies were zipping round far too rapidly for their gravity to keep them bound together in a cluster. By rights, they should have been flying…

IN TODAY’S universe, the three forces dealt with by the standard model have very different strengths and ranges. At a subatomic level, the strong force is the strongest, the weak the weakest and the electromagnetic force somewhere in between. Towards the end of the 1960s, though, physicist Steven Weinberg, then at Harvard University, showed with Abdus Salam and Sheldon Glashow that this hadn’t always been the case. At the kind of high energies prevalent in the early universe, the weak and electromagnetic forces have one and the same strength; in fact, they unify into one force. The expectation was that if you extrapolated back far enough towards the big bang, the strong force would also succumb, and be unified with the electromagnetic and weak force in one single superforce (see…

AT HALF past six on the evening of 20 January 2021, amid the gloom of a long winter lockdown, a small team met on Zoom to share a moment they knew might change physics forever. “I was literally shaking,” says Mitesh Patel at Imperial College London. He and his team were about to “unblind” a long-awaited measurement from CERN’s LHCb experiment. The measurement concerns bottom (also known as “beauty”) quarks, whose behaviour has long hinted at forces beyond our established understanding. That saga began in the mid-2000s when Gudrun Hiller, a theoretical physicist then at the University of Munich, Germany, was panning for insights in a flood of data > from the Belle experiment in Japan and the BaBar experiment in California. These “B-factories” produced bottom quarks by colliding electrons…