THE QUANTUM AGE HOW THE PHYSICS OF THE VERY SMALL HAS TRANSFORMED OUR LIVES BRIAN CLEGG 2 www.com Published in the UK in 2014 by Icon Books Ltd, Omnibus Business Centre, 39–41 North Road, London N7 9DP email: info@iconbooks.com Sold in the UK, Europe and Asia by Faber & Faber Ltd, Bloomsbury House, 74–77 Great Russell Street, London WC1B 3DA or their agents Distributed in the UK, Europe and Asia by TBS Ltd, TBS Distribution Centre, Colchester Road, Frating Green, Colchester CO7 7DW Distributed in South Africa by Jonathan Ball, Office B4, The District, 41 Sir Lowry Road, Woodstock 7925 Distributed in Australia and New Zealand by Allen & Unwin Pty Ltd, PO Box 8500, 83 Alexander Street, Crows Nest, NSW 2065 Distributed in Canada by Penguin Books Canada, 90 Eglinton Avenue East, Suite 700, Toronto, Ontario M4P 2YE 3 www.com Distributed to the trade in the USA by Consortium Book Sales and Distribution The Keg House, 34 Thirteenth Avenue NE, Suite 101 Minneapolis, Minnesota 55413-1007 ISBN: 978-184831-664-5 Text copyright © 2014 Brian Clegg The author has asserted his moral rights. No part of this book may be reproduced in any form, or by any means, without prior permission in writing from the publisher. Typeset in Melior by Marie Doherty Printed and bound in the UK by Clays Ltd, St Ives plc 4 www.com Contents Acknowledgements Introduction 1. Enter the quantum 2.
The electron’s realm 4. Light and magic 6. Making light work 8. Resistance is futile 9.
Floating trains and well-chilled SQUIDs 10. From bit to qubit 12. A quantum universe 5 www.com Index 6 www.com About the author Science writer Brian Clegg studied physics at Cambridge University and specialises in making the strangest aspects of the universe – from infinity to time travel and quantum theory – accessible to the general reader. He is editor of www.uk and a Fellow of the Royal Society of Arts.
His previous books include Inflight Science, Build Your Own Time Machine, The Universe Inside You, Dice World and Introducing Infinity: A Graphic Guide.com For Gillian, Chelsea and Rebecca 8 www.com Acknowledgements With thanks as always to my editor, Duncan Heath, for his help and support, and to all those who have provided me with information and assistance – you know who you are. One person I would like to mention by name is the late Richard Feynman, whose books enthralled me and who turned quantum theory from a confusing mystery to an exciting challenge.com Introduction The chances are that most of the time you were at school your science teachers lied to you. Much of the science, and specifically the physics, they taught you was rooted in the Victorian age (which is quite probably why so many people find school science dull). Quantum theory, special and general relativity, arguably the most significant fundamentals of physics, were developed in the 20th century and yet these are largely ignored in schools, in part because they are considered too ‘difficult’ and in part because many of the teachers have little idea about these subjects themselves.
And that’s a terrible pity, when you consider that in terms of impact on your everyday life, one of these two subjects is quite possibly the most important bit of scientific knowledge there is. Relativity is fascinating and often truly mind-boggling, but with the exception of gravity, which I admit is rather useful, it has few applications that influence our experience. GPS satellites have to be corrected for both special and general relativity, but that’s about it, because the ‘classical’ physics that predates Einstein’s work is a very close approximation to what’s observed unless you travel at close to the speed of light, and is good enough to deal with everything from the acceleration of a car to planning a Moon launch. But quantum physics is entirely different.
While it too is fascinating and mind-boggling, it also lies behind everything. All the objects we see and touch and use are made up of quantum particles. As is the 10 www.com light we use to see those objects. As are you.
As is the Sun and all the other stars. What’s more, the process that fuels the Sun, nuclear fusion, depends on quantum physics to work. That makes the subject interesting in its own right, something you really should have studied at school; but there is far more, because quantum science doesn’t just underlie the basic building blocks of physics: it is there in everyday practical applications all around you. It has been estimated that around 35 per cent of GDP in advanced countries comes from technology that makes use of quantum physics in an active fashion, not just in the atoms that make it up.
This has not always been the case – we have undergone a revolution that just hasn’t been given an appropriate label yet. This is not the first time that human beings have experienced major changes in the way they live as a result of the development of technology. Historians often highlight this by devising a technological ‘age’. So, for instance, we had the stone, bronze and iron ages as these newly workable materials made it possible to produce more versatile and effective tools and products.
In the 19th century we entered the steam age, when applied thermodynamics transformed our ability to produce power, moving us from depending on the basic effort of animals and the unpredictable force of wind and water to the controlled might of steam. And though it is yet to be formally recognised as such, we are now in the quantum age.com It isn’t entirely clear when this era began. It is possible to argue that the use of current electricity was the first use of true quantum technology, as the flow of electricity through conductors is a quantum process, though of course none of the electrical pioneers were aware that this was the case. If that is a little too concealed a usage to be a revolution, then there can be no doubt that the introduction of electronics, a technology that makes conscious use of quantum effects, meant that we had moved into a new phase of the world.
Since then we have piled on all sorts of explicitly quantum devices from the ubiquitous laser to the MRI scanner. Every time we use a mobile phone, watch TV, use a supermarket checkout or take a photograph we are making use of sophisticated quantum effects. Without quantum physics there would be no matter, no light, no Sun … and most important, no iPhones. I’ve already used the word ‘quantum’ thirteen times, not counting the title pages and cover.
So it makes sense to begin by getting a feel for what this ‘quantum’ word means and to explore the weird and wonderful science that lies behind it.com CHAPTER 1 Enter the quantum Until the 20th century it was assumed that matter was much the same on whatever scale you looked at it. When back in Ancient Greek times a group of philosophers imagined what would happen if you cut something up into smaller and smaller pieces until you reached a piece that was uncuttable (atomos), they envisaged that atoms would be just smaller versions of what we observe. A cheese atom, for instance, would be no different, except in scale, to a block of cheese. But quantum theory turned our view on its head.
As we explore the world of the very small, such as photons of light, electrons and our modern understanding of atoms, they behave like nothing we can directly experience with our senses. A paradigm shift Realising the very different reality at the quantum level was what historians of science like to give the pompous term a ‘paradigm shift’. Suddenly, the way that scientists looked at the world became different. Before the quantum revolution it was assumed that atoms (if they existed at all – many scientists didn’t really believe in them before the 20th century) were just like tiny little balls of the stuff they made up.
Quantum physics showed that they behaved so weirdly that an atom of, say, carbon has to be treated as if it is something totally different to a piece of graphite or diamond – and yet all that is inside that 13 www.com lump of graphite or diamond is a collection of these carbon atoms. The behaviour of quantum particles is strange indeed, but that does not mean that it is unapproachable without a doctorate in physics. I quite happily teach the basics of quantum theory to ten-year-olds. Not the maths, but you don’t need mathematics to appreciate what’s going on.
You just need the ability to suspend your disbelief. Because quantum particles refuse to behave the way you’d expect. As the great 20th-century quantum physicist Richard Feynman (we’ll meet him again in detail before long) said in a public lecture: ‘[Y]ou think I’m going to explain it to you so you can understand it? No, you’re not going to be able to understand it. Why, then, am I going to bother you with all this? Why are you going to sit here all this time, when you won’t be able to understand what I am going to say? It is my task to persuade you not to turn away because you don’t understand it.
You see, my physics students don’t understand it either. This is because I don’t understand it.’ It might seem that Feynman had found a good way to turn off his audience before he had started by telling them that they wouldn’t understand his talk. And surely it’s ridiculous for me to suggest I can teach this stuff to ten-year-olds when the great Feynman said he didn’t understand it? But he went on to explain what he meant. It’s not that his audience wouldn’t be able to understand what took place, what quantum physics described.
It’s just that no one knows why it happens the way it does. And because what it does defies common sense, this can 14 www.com cause us problems. In fact quantum theory is arguably easier for ten-year-olds to accept than adults, which is one of the reasons I think that it (and relativity) should be taught in junior school. But that’s the subject of a different book.
As Feynman went on to say: ‘I’m going to describe to you how Nature is – and if you don’t like it, that’s going to get in the way of your understanding it … The theory of quantum electrodynamics [the theory governing the interaction of light and matter] describes Nature as absurd from the point of view of common sense. And it agrees fully with experiment. So I hope you can accept Nature as she is – absurd.’ We need to accept and embrace the viewpoint of an unlikely enthusiast for the subject, the novelist D. Lawrence, who commented that he liked quantum theory because he didn’t understand it.
The shock of the new Part of the reason that quantum physics proved such a shocking, seismic shift is that around the start of the 20th century, scientists were, to be honest, rather smug about their level of understanding – an attitude they had probably never had before, and certainly should never have had since (though you can see it creeping in with some modern scientists). The hubris of the scientific establishment is probably best summed up by the words of a leading physicist of the time, William Thomson, Lord Kelvin. In 1900 he commented, no doubt in rounded, selfsatisfied tones: ‘There is nothing new to be discovered in physics. All that remains is more and more precise measurement.’ As a remark that he would come 15 www.com to bitterly regret this is surely up there with the famous clanger of Thomas J.
Watson Snr, who as chairman of IBM made the impressively non-prophetic remark in 1943: ‘I think there is a world market for maybe five computers.