Review

Schrödinger’s Kittens

by John Gribbin

‘The special theory of relativity tells us that it is impossible to run alongside a beam of light at the same speed the light is moving; relative to some chosen inertial frame, you can in principle get your own velocity up as close to the speed of light as you like without actually reaching it – but no matter how close you get, when you measure the speed of the light beam itself you will always get the answer c.’

If you read my reviews you’ve probably noticed that occasionally I write about science books. The problem with scientific thought is that it dates very quickly. Books come and go and by the time you begin to grasp a new concept the world has moved on. Someone has come up with a new theory which supplants or modifies the first one.

Nowhere and nowhen is this more evident than in the field of quantum mechanics. Whilst Einstein’s theories of relativity come out relatively (and relativistically) unscathed after a whole century, quantum physics is moving forward at light speed. This is well illustrated by John Gribbin’s book Schrödinger’s Kittens.

When I first read it shortly after it came out in 1995 it was new and fresh. Now, in the face or more recent works, like Carlo Rovelli’s Reality Is Not What  It Seems, or even one of Hawking’s more recent ‘popular’ science books like The Grand Design, Schrödinger’s Kittens may belong to history. But before we consign it as such to the dusty corner of the library, spare a few moments to consider it more carefully.

‘If, as quantum theory suggests, the world only exists because it is being observed, then it is also true that the world only changes because it is not being observed all the time.’

Schrödinger’s Kittens is a sequel to an earlier scientific bestseller by Gribbin, In Search of Schrödinger’s Cat, published in the mid eighties. Most people, even if they are not scientists, will have heard of this famous cat, the one in the box that can be ‘alive and dead at the same time.’ Of course, it’s not as simple as that. The imaginary cat is part of a thought experiment which demonstrates the weirdness of quantum theory and endeavours to explain part of it by reference to familiar objects. On the way, it introduces unfamiliar concepts like ‘wave function’ and ‘superposition of states.’

If you think the cat is weird, just wait until you read about her offspring! Let me try and describe this ‘experiment’ in simplistic terms: each of the two kittens is also in a box but though one is sitting right here on Earth, the other is somewhere thousands of light years away, shall we say, in Andromeda [not that far away maybe in galactic terms but far enough]. Now, open our box and find a live kitten and you can be sure the other is dead – and vice versa.

‘You could argue that the act of observation sends a signal not just across space but also echoing back in time …’

All flippancy aside, Schrödinger’s Kittens, though it deals with the consequences of this imaginary experiment, is about a great deal more than quantum entanglement. John Gribbin begins his book with an historical survey of both classical theories (Einstein’s Relativity) and quantum mechanics. By the beginning of the eighties, the favourite theory of how light waves/particles behave had long been the so-called Copenhagen Interpretation. However, already other ideas were being discussed among physicists, including the ‘sum-over-histories’ of Richard Feynman and the many worlds interpretation of Wheeler and Everett.

By 1995 there were many more variations and the disagreements about which theory is correct, the author suggests, are not always resolved peacefully – the term ‘mud-slinging’ was used ….. Indeed, the title for the present article came (with one minor modification) from yet another book, published in 1986, by Paul Davies, a physics professor, and Julian Brown, a BBC Radio producer. The Ghost in the Atom contains a transcript of interviews with eight prominent scientists, each asserting – often vehemently – that their version of quantum theory was the correct one.

Gribbin himself favours the many worlds theory but to his credit points out that we can learn something from them all. Without most of us realising it, quantum ideas have become part of our everyday lives. Computers, transistors, mobile phones, lasers, Blu-ray players and many other conveniences depend on actions at the quantum level. Without quantum physics we wouldn’t have WordPress or Youtube, which means that quantum physics is something that affects us all. It is something we should all know at least a little about.

‘… an atom is really [only] a theoretical model of reality….not only do we not know what an atom is “really”, we cannot ever know what an atom is “really”. We can only know what an atom is like.’

If you have the stomach for the detail of this strange and incomprehensible world, read the whole book. As both scientist and journalist, Gribbin’s talent lies in putting extremely complex ideas in terms even the non-scientist can – with a bit of patience – understand. As well as a comprehensive look at the world of elementary particles, he delves into philosophical concepts. Does history really exist, he asks, or is it simply a consistent set of present memories?

If you’re the sort of reader with a practical turn of mind, you may care to carry out  Gribbin’s experiment with the Polaroid sunglasses and try to figure out what is happening.***

On the other hand, quantum mechanics may not be for you. So, if you are skimming or, having got to around page 100 your eyes are beginning to glaze over , I strongly recommend you jump to Chapter Five. It’s entitled ‘Thinking About Thinking About Things’ and includes possibly the best essay on the meaning of reality I have ever read.

‘The very workings of our brains themselves depend on the same kind of chemistry – that is, on the exchange of photons.’

*** But please don’t try the cat experiments at home!

*****