A Game of Theories
I’m about to make a start on a new book with the working title: A Game of Theories: The Quest for the Essential Meaning of Quantum Mechanics (I’m pretty confident that this title won’t survive to publication). I’ve spent the last couple of days bedding down the structure and approach, and have tried to sharpen my thinking by working on the opening Preamble. I’ve decided to post the Preamble here, and invite readers to let me know what they think. You can get some idea of what the book will be all about from its list of contents, which I’ve appended at the end.
I know why you’re here.
You know that quantum mechanics is an extraordinarily successful scientific theory, on which much of our modern, tech-obsessed lifestyles depend, from smartphones to streaming to satellites. You also know that it is completely bonkers. Its discovery forced open the window on all those comfortable notions we had gathered about physical reality from our naïve interpretation of Isaac Newton’s laws of motion, and unceremoniously shoved them out. Although quantum mechanics quite obviously works, it leaves us chasing ghosts and phantoms; particles that are waves and waves that are particles; cats that are at once both alive and dead; lots of seemingly ‘spooky’ goings-on; and a desperate desire to lie down quietly in a darkened room.
But, hold on. If we’re prepared to be a little more specific about what we mean when we talk about ‘reality’ and a little more circumspect in the way we think a scientific theory might represent such a reality, then all the mystery goes away.
I’m not kidding. I have a bit of a reputation as the kind of guy you might find in the kitchen at parties; the kind who spoils all the fun, bursting the bubbles of excitable mystery and urban legend (what Americans sometimes call ‘woo’) with a cold scepticism and a calculating rationality. Spock, not Kirk. One commentator recently called me ‘depressingly sane’. This is a badge I’m happy to wear with pride. There are many popular books you can buy about the weirdness and the ‘woo’ of quantum mechanics. This isn’t one of them. And in any case that’s not why you’re here.
But – let’s be absolutely clear – a book that says ‘Honestly, There Is No Mystery’ would not only be a bit dull and uninteresting (no matter how well it was written), it would also be completely untrue. For sure we can rid ourselves of all the mystery in quantum mechanics but only by abandoning any hope of deepening our understanding of nature. We must become content to use the quantum representation simply as an instrument to perform calculations and make predictions, and we must resist the temptation to ask: But how does nature actually do that? And there lies the rub: for what is the purpose of a scientific theory if not to aid our understanding of the physical world?
Let’s be under no illusions. The choice we face is a philosophical one. There is absolutely nothing scientifically wrong with a depressingly sane interpretation of quantum mechanics in which there is no mystery. If we choose instead to pull on the loose thread we are inevitably obliged to take the quantum representation at face value, and interpret its concepts rather more literally. Surprise, surprise. The fabric unravels to give us all those things about the quantum world that we find utterly baffling, and we’re right back where we started.
My purpose in this book is (hopefully) not to spoil your fun, but to try to explain what it is about quantum mechanics that forces us to confront this kind of choice, and why this is entirely philosophical in nature. Making different choices leads to different interpretations or even modifications of the quantum representation and its concepts, in what I call (with acknowledgements to George R.R. Martin) a game of theories.
I will tell you about the rules of this game in Part I, based on a pragmatic but perfectly reasonable understanding of what we mean by ‘reality’; the purpose of a scientific representation of this reality; a brief summary of everything you might need to know about quantum mechanics; and the scene that was set by Albert Einstein’s great debate with Niels Bohr in the late 1920s and early 1930s.
We will then go on in Part II to look at various attempts to play the game, from the original, so-called Copenhagen interpretation, through relational quantum mechanics; consistent histories; quantum Bayesianism; hidden variable theories of local (Bell’s inequality), crypto non-local (Leggett’s inequality), and non-local (pilot waves) varieties; theories based on a kind of quantum ‘friction’ called decoherence; theories based on human consciousness; and the many worlds interpretation.
If you will indulge me, through all of this I will make use of a no doubt over-fanciful analogy. This is based on the notion that the game of theories involves navigating the ‘Ship of Science’ on the perilous ‘Sea of Representation’. Yes, I’ve obviously read too many fantasy novels.
We sail the Ship back and forth between two shores. These are the deceptively welcoming, soft, sandy beaches of metaphysical ‘reality’ (always in quotes) and the broken, rocky and often inhospitable shores of empirical reality. The former are shaped by our abstract imaginings, free-wheeling creativity, and personal values and prejudices. These become translated into one or more metaphysical preconceptions, which summarise how we think or even believe nature should be. These are beliefs that, by their nature, are not supported by empirical evidence. So, if you prefer you could call these preconceptions articles of ‘faith’, echoing one of my favourite Einstein quotes: ‘I have no better expression than the term “religious” for this trust in the rational character of reality and in its being accessible, to some extent, to human reason’.
Examples of such preconceptions might include: ‘the description of nature must be beautiful’, or ‘natural’, or ‘based on strict cause-and-effect principles’, ‘completely pre-determined’, ‘observe strict conservation laws’, and so on. In their turn these preconceptions mould our scientific ideas and hypotheses:
- If there is no such thing as absolute space and time, it follows that [insert scientific idea here];
- If matter is particulate, shouldn’t light be particulate, too? It follows that [insert scientific hypothesis here];
- If ‘God does not play dice’, it follows that [insert scientific idea here];
- And so on.
You get the basic idea.
Scientific ideas and hypotheses are all very well, but to make a scientific theory we must either sail the Ship to the rocky shores of empirical reality or (preferably) begin our journey here. This is where we discover how nature actually appears, as revealed in the rather brutal, hard facts of observational and experimental data. We can then sail the Ship back and forth as often as we need in order to strengthen the relationships between the representation afforded by our theory and the empirical facts.
Within this Sea I have charted two grave dangers. The rock shoal of Scylla lies close to the shores of empirical reality. It is a rather empty instrumentalism, perfectly empirically adequate but devoid of any real physical insight and understanding. Charybdis lies close to the beaches of metaphysical ‘reality’. It is a whirlpool of wild, unconstrained metaphysical nonsense. The challenge to theorists is to discover safe passage across the Sea of Representation. In A Game of Theories I want to explain why this has proven so darn difficult, and why I have a very bad feeling about it.
So, welcome. You’re here because you want answers. Please take a seat and make yourself comfortable, and I’ll go and put the kettle on.
Part I: The Rules of the Game
1 Just What is This Thing Called ‘Reality’, Anyway? Metaphysical Preconceptions and Empirical Reality
2 Setting Sail on the Sea of Representation How Scientific Theories Work (and Sometimes Don’t)
3 The Complete Guide to Quantum Mechanics (Abridged) Everything You’ve Ever Wanted to Know, With FAQs
4 When Einstein Came Down to Breakfast Because You Can’t Write a Book About Quantum Mechanics Without a Chapter on the Bohr-Einstein Debate
Part II: Playing the Game
Quantum Theory is Complete…
5 So Just Shut Up and Calculate The View from Scylla: Copenhagen and the Relational Interpretation
6 But We Need to Reinterpret What it Says Consistent Histories and QBism
Quantum Theory is Incomplete…
7 So We Need to Add Some Things Local, Crypto Non-local, and Non-local Hidden Variables
8 So We Need to Add Some Other Thing Decoherence, Entropy, and the Arrow of Time
9 Because We Need to Include My Mind (Or Should that be Your Mind?) Wigner’s Friend and the Ghost in the Machine
10 Because … Okay, I Give Up The View from Charybdis: Many Worlds and the Multiverse
Epilogue: A Very Bad Feeling
 This was theoretical physicist Sabine Hossenfelder, referencing my book Farewell to Reality: How Fairy-tale Physics Betrays the Search for Scientific Truth, in a tweet dated 11 March 2018.
 Albert Einstein, quoted in Maurice Solovine, Albert Einstein: Lettres à Maurice Solovine, Gauthier-Villars, Paris, 1956. This quote is reproduced in Arthur Fine, The Shaky Game: Einstein, Realism and the Quantum Theory, 2nd edition, University of Chicago Press, 1986, p.110.
 The development of quantum theory (and quantum field theory) were indeed driven by often baffling empirical data that theorists struggled to explain – the theorists were obliged to set sail from the shores of empirical reality. But since about the mid-1970s, theorists started to run out of signposts provided by data and have increasingly relied on their metaphysical preconceptions for guidance. They started to set sail from the all-too-welcoming shores of metaphysical ‘reality’. Consequently, many contemporary theorists are now lost at sea.