Gribbin: Schroedinger's Kittens
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John Gribbin, Schrödinger's Kittens and the Search for Reality : Solving the Quantum Mysteries. Boston : Little Brown and Company, 1995. ix + 261 pages; illustrated with line drawings; with bibliography and index.
This is a book written with nonspecialist readers in mind, but I'd say it assumes that some ideas about quantum physics are already familiar. If the "Copenhagen interpretation" is a familiar idea then the material in Schrödinger's Kittens won't be so hard to follow – except to the extent that there are new and challenging ideas in Gribbin's writing. Somewhat more facetiously, if the title, "Schrödinger's Kittens", is suggestive and somewhat amusing, your prerequisites are probably in place. The author says that this book starts where his In Search of Schrödinger's Cat left off; perhaps that's the book to read first, but I can't comment yet because I read this one first.
The basic quandary that Gribbin examines is this: the quantum world of the very small evidently doesn't work like the human-sized world, so how can we understand it? What is reality?
In considering the question Gribbin looks at a number of aspects of quantum theory, but focuses particularly of aspects of how we interpret what it means. As with all physical theories, there are the equations of the theory that give their perfectly useful answers about how the world works, but the equations themselves don't tell us what the symbols in the equations really mean, only how the things represented by those symbols interact or relate to each other. The equations are accompanied by interpretations that try to attach some physical-world meaning to the symbols in the equations.
It makes for fun reading, although one does have to keep one's wits about one. The main interpretation of quantum theory is known as the "Copenhagen interpretation", an interpretation that we've had since the earliest days of the theory, the interpretation conferred on the theory by Niels Bohr.
Note particularly that the "interpretation" is an adjunct to the theory, not the theory itself. Coming as it did from Bohr, many people take the Copenhagen interpretation as scientific gospel. It is not. I've never cared for the Copenhagen interpretation and I'm happy to report that Gribbin doesn't like it either. Searching for a better interpretation of quantum mechanics is what this book is about.
Along the way there are a number of misguided notions about quantum mechanics and its interpretation that needed clearing up. Early on Gribbin takes on the notorious Heisenberg uncertainty principles and their mistaken interpretations. I had plenty of early textbooks in my student days that failed just as Gribbin explains, by trying to explain uncertainty as more a failure of experimentation rather than a fundamental principle.
This [inability to measure to arbitrary precision] is not, as some textbooks still mistakenly suggest, solely a result of the practical difficulty of making measurements. It is not simply because in measuring the position of the electron (perhaps by bouncing photons off it) we give it a kick, which changes its momentum. A quantum object does not have a precisely defined momentum and a precisely defined position. The electron itself does not "know" within certain limits where it is or where it is going. Exaggerating only slightly, if it knows exactly where it is, it doesn't know where it is going at all; if it knows exactly where it is going, it doesn't have the faintest idea where it is. Usually, though, a quantum object has an approximate idea of both where it is and where it is going. But the important word here is 'approximate'; hard though it is to understand from the 'common-sense' viewpoint of our everyday world, the quantum entity cannot be pinned down to a definite location, and there is always some uncertainty about where it is going. [p. 17]
Then there's that whole business of Schrödinger's Cat. It's my sense that Schrödinger conceived of the diabolical "thought experiment" with the doomed cat to mock the Copenhagen interpretation but that somehow the whole deal got absorbed into the mysticism that grew up around quantum theory—aided and abetted by a number of science popularizers, not to mention quite a few physicists themselves.
Gribbin does a good job of scraping away the mystical encrustations and tossing out the unnecessary accumulations of the metaphysical trash that have collected, but there are still mysteries aplenty left to entertain us, but real mysteries whose answers have profound implications for how we understand the world of the very small and reality itself. I found quite a few thoughts provoked by Gribbin's writing in a good way, and quite a few new and useful ways of thinking about the things he discussed.
There is something very tricky about time, and this trickiness is intimately linked with the nature of quantum reality, and the problem of reconciling the equations of quantum mechanics with those of the everyday world. [p. 175]
I was easily convinced that I have almost no understanding of what time really is by the time I read this statement, but maybe I have new ways to think about it. At that point in the book I easily agreed that "there is something very tricky about time". I also now understand that the answer is tied up in the fact that, for light (or photons), time does not exist.
The point is that everything we 'know' about the quantum world is based on inferences and observations of things in the everyday world. Physicists deal in models, which are approximations to (they hope) some underlying reality. But they often forget to distinguish between those models and reality itself, while our preconceptions and cultural influences colour the very way in which we begin to think about the way the world works. [p. 183]
It all tends to sound very metaphysical in my discussion and the excerpts I've chosen. I suppose that's because it is. When Gribbin says he's interested in searching for reality, that's exactly what he means. I was quite satisfied, though, that his metaphysics was firmly grounded in unshakable scienticity and a depth of understanding one is unlikely to find in most popular science writing.
-- Notes by JNS