Universe a grand tour of modern science Phần 1 pptx

[...]... LSE means London School of Economics, although in fact Hamilton had done most of the work at Imperial College London, which might have been more respectable from the point of view of a natural-sciences editor American Naturalist carried the landmark paper instead Hamilton’s theory indicated that evolution should have strongly favoured rampant tribalism and associated cruelty Its author took a dark and... supplying the mass of the Earth, the Universe initially made the equivalent of 2-billion-and-one Earths and threw 2 billion away in mutual annihilation The traces of the vanished surplus are all around us in the form of invisible radiation Yet even so small a discrepancy in the production of matter and antimatter was sufficient for Sakharov to call the Universe skewed And in his 19 67 paper he seized... mirrorimage properties 16 a n t i m at t e r If a particle meets its antiparticle they annihilate each other and disappear in a puff of gamma rays This happens night and day, above our heads, as cosmic rays coming from our Galaxy create positrons, and electrons in the atmosphere sacrifice themselves to eliminate them Yet the count of electrons does not change Whenever a cosmic ray makes a positron it also... electron spins about an axis, like a top But out of Dirac’s equations popped another particle, a mirror-image of the electron The meaning of this theoretical result was mystifying and controversial, but Dirac was self-confident enough to talk about an anti-electron as a real entity, not just a mathematical fiction Also sure of himself was Carl Anderson of Caltech, experimenting with cosmic rays coming... In 19 32 he saw a lightweight particle swerving the wrong way under the influence of a magnet and decided that he had an anti-electron, even though he hadn’t heard about Dirac’s idea The anti-electron has the same mass as the electron but an opposite electric charge, and it is also called a positron Anderson’s positron was just the first fragment of antimatter For every particle there is an antiparticle... them head on, within a 12 00-tonne detector devised to spot newly created neutral Bs breaking up after a million-millionth of a second More than 600 scientists and engineers from 75 institutions in Canada, China, France, Germany, Italy, Norway, Russia, the UK and the USA took part in the Stanford venture That roll call was a sign of how seriously the Sakharov scenario was taken So was a price tag of well... eventually give the answer At CERN in Geneva, thanks mainly to Japanese funding, the gamble at the turn of the century was to construct anti-atoms, and to look for any slight differences in their behaviour compared with ordinary atoms Although physicists had been making the separate components of an antihydrogen atom for many years, to put a positron into orbit around an antiproton was easier said than... matter and antimatter, it should all have disappeared again, in mutual annihilation, leaving the cosmos completely devoid of matter Well, the Universe is pretty empty Just look at the night sky That means you can narrow the problem down, as Sakharov did For every billion particles of antimatter created you need only 1, 000,000,0 01 particles of matter to explain what remains To put that another way, in supplying... should be equally likely, with the directions of the emissions reversed Lee and Yang predicted a failure of parity conservation 17 a n t i m at t e r An experimentalist from China, Chien-Shiung Wu, was also based at Columbia, and she put parity to the test in an experiment done at the US National Bureau of Standards She lined up the nuclei of radioactive atoms in a strong magnetic field and watched them... right back to re-examining the axiom of the Sakharov scenario, that all antimatter was wiped out very early in the history of the Universe If, on the contrary, significant amounts have survived, antihelium would be a signature Antiprotons from antihydrogen won’t do, because they are too easily made in present-day collisions of ordinary cosmic-ray particles The fleeting creation of antimatter is easy to . Data Data available Library of Congress Cataloguing in Publication Data Data available Typeset in 11 /13 pt Dante by SPI Publisher Services, Pondicherry, India Printed in Great Britain on acid-free paper. Toronto With offices in Argentina Austria Brazil Chile Czech Republic France Greece Guatemala Hungary Italy Japan Poland Por tugal Singapore South Korea Switzerland Thailand Turkey Ukraine Vietnam Oxford. origins of those human alternatives Antimatter 15 Does the coat that Sakharov made really explain its absence? Arabidopsis 24 The modest weed that gave plant scientists the big picture Astronautics