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Quantum Manjit Kumar.pdf

'This is about gob-smacking science at the far end of reason ... Take it nice and easy and savour the experience of your mind being blown without recourse to hallucinogens' Nicholas Lezard, Guardian For most people, quantum theory is a byword for mysterious, impenetrable science. And yet for many years it was equally baffling for scientists themselves.In this magisterial book, Manjit Kumar gives a dramatic and superbly-written history of this fundamental scientific revolution, and the divisive debate at its core. Quantum theory looks at the very building blocks of our world, the particles and processes without which it could not exist.Yet for 60 years most physicists believed that quantum theory denied the very existence of reality itself. In this tour de force of science history, Manjit Kumar shows how the golden age of physics ignited the greatest intellectual debate of the twentieth century.Quantum theory is weird. In 1905, Albert Einstein suggested that light was a particle, not a wave, defying a century of experiments. Werner Heisenberg's uncertainty principle and Erwin Schrodinger's famous dead-and-alive cat are similarly strange. As Niels Bohr said, if you weren't shocked by quantum theory, you didn't really understand it.While "Quantum" sets the science in the context of the great upheavals of the modern age, Kumar's centrepiece is the conflict between Einstein and Bohr over the nature of reality and the soul of science. 'Bohr brainwashed a whole generation of physicists into believing that the problem had been solved', lamented the Nobel Prize-winning physicist Murray Gell-Mann. But in "Quantum", Kumar brings Einstein back to the centre of the quantum debate. "Quantum" is the essential read for anyone fascinated by this complex and thrilling story and by the band of brilliant men at its heart.

Quantum Manjit Kumar.pdf

Paul Ehrenfest was in tears. He had made his decision. Soon he would attend the week-long gathering where many of those responsible for the quantum revolution would try to understand the meaning of what they had wrought. There he would have to tell his old friend Albert Einstein that he had chosen to side with Niels Bohr. Ehrenfest, the 34-year-old Austrian professor of theoretical physics at Leiden University in Holland, was convinced that the atomic realm was as strange and ethereal as Bohr argued.

By the early 1920s it had long been apparent that the advance of quantum physics on an ad hoc, piecemeal basis had left it without solid foundations or a logical structure. Out of this state of confusion and crisis emerged a bold new theory known as quantum mechanics. The picture of the atom as a tiny solar system with electrons orbiting a nucleus, still taught in schools today, was abandoned and replaced with an atom that was impossible to visualise. Then, in 1927, Werner Heisenberg made a discovery that was so at odds with common sense that even he, the German wunderkind of quantum mechanics, initially struggled to grasp its significance. The uncertainty principle said that if you want to know the exact velocity of a particle, then you cannot know its exact location, and vice versa.

The nearly simultaneous publication of two popular histories of quantum mechanics, each highly readable and basically reliable, speaks well about the growing public interest in modern physics and about the commitment of major publishers to respond.

Both authors would have been helped by a closer look at the well-known re-analysis of Bell's argument, introduced in 1984 by Jon Jarrett and refined by Shimony. Jarrett showed that the original Bell locality condition is a conjunction of two logically independent conditions that Shimony called outcome independence and parameter independence. The former is akin to a denial of quantum entanglement, the latter to relativistic locality constraints. Experimental violations of the Bell inequality can now be traced to violations of one or the other of these two conditions. That there are two independent routes to violations of the Bell inequality makes it clear how orthodox quantum mechanics, which presumes entanglement, and a Bohm-type hidden variables theory, which assumes relativistic non-locality at the microlevel, can both claim to have been vindicated by the Bell experiments. But these gentle criticisms should not deter the interested reader from enjoying two welcome additions to the popular history of twentieth-century physics.

Two theories have shaped modern physics and thus our understanding of the world: quantum mechanics and general relativity. The relativity deals with huge scale systems and gravity - and works, while in the process creating its own well know paradoxes. Quantum mechanics applies at the atomic (and lower) levels. Of the two, it's the quantum mechanics that is - and has been - the most mind boggling for scientists and laymen alike.

Niels Bohr said that if anybody says that they understand quantum mechanics that means they don't really understand it. Richard Feynman suggested that one should try, if at all possible, just to accept that it is like that instead of wondering how it could possibly be like that. Albert Einstein struggled with the quantum demon for many years, and his famous quote about God not playing dice is connected to those struggles.

And yet quantum mechanics is an incredibly fruitful theory, which successfully explains and describes most fundamental phenomena of our whole world: it allows us to peek into the very core of matter, at the forces creating and governing the infinitesimal particles constituting the atoms of which constitute everything in the Universe.

Kumar's Quantum is a historical narrative of the development of the quantum theory, from the first reluctant introduction of the term quantum (and its implications) by Max Planck to the development of the whole theory by Niels Bohr and his troop of Young Turks of theoretical physics which included Heisenberg, Dirac and Pauli and its solidification in so-called Copenhagen interpretation; and beyond, to the most recent attempts at testing the same interpretation.

Throughout the book, Kumar repeatedly focuses on philosophical antecedents and consequences of what he calls in the subtitle the Great Debate About the Nature of Reality. The figure of Einstein is fundamental to Kumar's argument, and especially in the second half of Quantum he shows how Einstein's doubts kept the philosophical debate - and the search for new interpretations - of quantum theory alive even when the great majority of the scientists subscribed to the orthodox Copenhagen version.

Einstein himself started the quantum ball rolling, but could never come to terms with what became the dogma of quantum mechanics - the so called Copenhagen interpretation derived by Bohr, Pauli and Heisenberg.

Many are familiar with the famous Einstein's claim of God not playing dice, which is normally taken to indicate Einstein's unshakable belief in causality in a deterministic world. This belief is profoundly shaken by the quantum theory, according to which atomic world is probabilistic in its essence. But there was something in quantum mechanics that troubled Einstein (and Schrödinger: his famous thought experiment intended to show the absurd implications of the Copenhagen interpretation of quantum mechanics, not to support it) even more than the loss of causality and its replacement by statistical models only. 350c69d7ab


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