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Long before I ever heard of smartphones, or the C++ programming language, or even C, I was intrigued by quantum mechanics. In November 1979, as a sophomore undergraduate, I was fascinated to read an article in the latest edition of the Scientific American: “The Quantum Theory and Reality”, written by French theoretical physicist Bernard d’Espagnat. As recorded in the Wikipedia article on d’Espagnat, this article contains the stunning quote,

The doctrine that the world is made up of objects whose existence is independent of human consciousness turns out to be in conflict with quantum mechanics and with facts established by experiment.

What particularly struck me was the claim that “facts established by experiment” were at odds with common-sense ideas about reality. These experiments involved the now-famous “correlation at a distance” experiments inspired by a paper originally authored in 1935 by Albert Einstein and two co-workers: Boris Podolsky and Nathan Rosen. The initials of the authors – EPR – became synonymous with these experiments. Particularly when viewed through the analysis of John Bell, who devised some surprisingly counter-intuitive inequalities applicable to correlations between results in EPR experiments, these experiments seemed to defy all explanation.

Early in 1980, Professor Mary Hesse of the History and Philosophy of Science department at Cambridge, gave one of the then-frequent lunchtime presentations on mathematical topics, to students (like me) sufficiently interested in such topics to give up their free time in pursuit of greater understanding of mathematics. Prof Hesse chose the philosophical problems of quantum mechanics as her subject for the meeting. I listened carefully, to find out if there were any good rebuttals to the claims made by d’Espagnat. My conclusion was that the whole area was decidedly weird. As months passed, I also asked various maths lecturers about this – but their advice was generally not to think about these questions!

Several years later, I chose Philosophy of Science as the area for my postgraduate studies, with a particular focus on trying to make sense of quantum mechanics. During that time, I even made my first trip to Finland – not to visit Nokia (since I had never heard of them at that time), but to attend a conference in 1985 in pictureseque Joensuu. It was a conference to commemorate 50 years since the publication of the EPR paper. Nathan Rosen, then aged 76, was the guest of honour.

The more I studied the philosophical problems of quantum mechanics, the more I came to respect what initially seemed to be the weirdest and most unlikely solution of all. This is the so-called “Many worlds” interpretation (though, as it turns out, the name is misleading):

• Originally proposed by Hugh Everett III, in 1957;
• It refuses to introduce some kind of demarcation between the quantum realm, where superposition (“wavelike behaviour”) is allowed, and the classical realm, where things need to be more definite;
• Instead, it takes very seriously the idea that macroscopically large objects also spread out over a range of diverse states – in a so-called quantum superposition;
• This includes the shocking and apparently absurd notion that even we humans end up (all the time) in a superposition of different states;
• For example, although I subjectively feel, as I type these words now, that this is the unique instance of myself, there are countless other instances of myself, spread out in a wider multiverse, all having diverged from this particular instance as a result of cascading quantum interactions;
• In some of these other instances, I am employed by companies other than Symbian (my employer for the last ten years in this instance); in yet other instances, Symbian was never created, or I remained in academia instead of joining the world of business, or human civilisation was destroyed when the Cuban missile crisis went wrong, or the values of physical constants were not capable of giving rise to complex mater – and so on.

If objections to this idea come to your mind, it’s very likely that the same objections came to my mind during the years I pursued my postgraduate studies. For example, to the objection “why don’t we feel ourselves splitting”, comes the reply given by Hugh Everett himself:

Well, Copernicus made the analysis that the Earth was moving around the sun, undoing thousands of years of belief that the sun was going around the Earth, and people asked him, If the Earth is moving around the sun, then why don’t I feel the Earth move?

In time, I deprioritised my postgraduate studies, to take a series of jobs, first as a part-time university supervisor, then as a maths tutor at a sixth form college, and then (from 1988) as a software engineer. But occasionally, I come across a link that re-awakens my fascination with quantum theory and the many worlds interpretation. Recently, there have been quite a lot of these links:

• The son of Hugh Everett is a reasonably famous singer and guitarist in his own right – Mark Everett, also sometimes known as “Mr E” or just “E”;
• Mark Everett has just released an autobiography “Things the Grandchildren Should Know” which addresses his growing awareness of his father’s remarkable thinking (Hugh Everett died, of a heart attack, in 1982, when Mark was just 19);
• There has also been a PBS documentary on this same topic, “Parallel worlds, parallel lives“, which has generated considerable media interest (such as this piece in the Scientific American);
• Coincidentally, various conferences have taken place in the last year or so, commemorating the fiftieth anniversary of Everett’s original thesis;
• For example, several people I remember from my own postgraduate studies days took part in a conference “Everett at 50” at Oxford.

With this growing abundance of material about Everett’s ideas, I’d like to highlight what I believe to be among the best book on the subject. It’s “Schrodinger’s Rabbits: The Many Worlds of Quantum“, written by Colin Bruce. It deserves to be a lot better known:

• The author has a pleasant writing style, mixing in detective story writing and references to science fiction stories, with analysis of philosophical ideas;
• There’s no complex maths to surmount – though the reader will have to think carefully, going through various passages (the effort is worth it!);
• Unlike many books which seem to repeat the same few themes spread over many chapters, each chapter in this book introduces important new concepts – which is another reason why it’s rewarding to read it;
• The book highlights some significant difficulties faced by the many worlds theories, but still (in my view) makes it clear that these theories are more likely to be true than false.

Alternatively, for a book that is even wider in its scope (though less convincing in some of its arguments), try “The Fabric of Reality: The Science of Parallel Universes and Its Implications” by David Deutsch – who in addition to breaking new ground in thinking about the philosophy of quantum mechanics, also happens to be a pioneer of the theory of quantum computing.

Finally, for a book that generally leaves readers in no doubt that any “common sense” interpretation of quantum mechanics fails, take a look at the stunningly well-written “Quantum Reality: Beyond the New Physics” by Nick Herbert.