Magicians reveal what the world's all about

For several years, I've been fascinated by the popular books of three physicists: Brian Greene, David Deutsch and Lawrence Krauss.

Funnily enough, although the three of them are writing about the same general subject—our state-of-the-art understanding of the nature of the universe—they rarely, if ever, get around to handling the same questions in comparable, if not similar, fashions. Moreover, in their latest books, they hardly even refer to one another's work.

It's easy to understand superficially why Greene, Deutsch and Krauss don't seem to have a lot to say to one another. Greene has been reputed for a long time as an adept of string theory, and there's no reason to imagine that the other two physicists are particularly keen on this theory. Earlier this year, Krauss became widely known through his presentation of an esoteric explanation of how the ultimate "free lunch"—obtaining something from nothingness—is a perfectly plausible phenomenon at a cosmic level.

As for the 59-year-old Oxfordian David Deutsch, he comes through to me as the most philosophical member of the trio. Indeed, he offers us a multiverse view of existence that is totally amazing. As in his first book, The Fabric of Reality, Deutsch pursues in The Beginning of Infinity his quest for a Theory of Everything inspired by the work of a somewhat heteroclite foursome: Karl Popper (epistemology), Hugh Everett (multiverse theory), Alan Turing (computation) and Richard Dawkins (evolution). Indeed, between the Popperian explanations of knowledge, the connotations of quantum theory leading to the existence of multiple universes, the vast theories of classical computing put forward by Turing (which are no doubt sufficient to handle, not only the DNA computer responsible for replication and life, but also the phenomena of neuronal computing) and finally the processes of Darwinian evolution and genetics so brilliantly presented by Dawkins, most observers would agree that we've no doubt covered many of the basic essentials of a scientific outlook on reality. Deutsch himself refers to these four grand dimensions of his global philosophical approach as strands (a word I like, which evokes weaving a fabric).

A few weeks ago, I was excited to learn that Deutsch has been working on a kind of fifth strand, of a subterranean nature, which he calls constructor theory. If you've got 47 minutes of free time, I urge you to click here to listen to Deutsch himself presenting this work. Basically, it's a matter of trying to understand why certain things are possible (even though they may have never actually happened yet) whereas countless other potential events are impossible because certain laws of physics have "blacklisted" them forever. In other words, he has enhanced astronomically the sense of the concept of possibility, to the point of claiming that anything and everything is strictly possible... provided only that we know of no law of physics that forbids such a happening, and therefore renders it impossible. Deutsch draw our attention to the strict binarity of the situation. Between the impossible (ruled out by physics) and the possible, there is no third way out. On the one hand, nothing—not even the most extravagant events—should be branded as theoretically impossible unless we are already aware of a law of physics that forbids such things. On the other hand, everything else should be thought of as theoretically possible.

In his eagerness to point out the counterintuitive nature of this thinking, Deutsch hit upon an amusing easy-to-grasp example, which goes straight to the heart of my Antipodes blog. Most of us agree that people on the other side of the planet Earth are in an upside-down position with respect to us, and vice versa.

That old Epinal image is funny but quite silly, of course, because nobody really believes that Antipodeans get around on their hands, with their Hobbit-like feet stretching towards the heavens. But are we truly ready to admit that the heads of Antipodeans point constantly in the opposite direction to our own heads? If technology were to offer me a magical real-time closeup view of Antipodeans, in strict conformity with our mutual orientations, in the same way that binoculars enable me to observe distant objects through my bedroom window, would I not be somewhat surprised to receive upskirt images of Antipodean ladies whose heads appear to be receding upwards into the sky? My surprise (which would be inevitable, I think) would seem to confirm that, to a certain extent, I've never really believed wholeheartedly that the heads of Antipodeans point in the opposite direction to mine. And David Deutsch considers that this mild form of surprise, or doubt, reflects my persistent quest for a third way out, between the possible and the impossible. My scientific culture persuades me that there is no law of physics that would forbid Antipodeans from getting around in an upside-down position with respect to me. So, I conclude that it's perfectly possible for this to be the case. At the same time, I consider that modern laws of celestial mechanics have quashed forever all remnants of flat-Earth theories, meaning that it's unthinkable that the heads of Antipodeans might point in the same direction as mine. And yet I don't seem to have gone one tiny step further and admitted explicitly, in a tangible concrete sense, that people down on the opposite side of the planet are truly presenting me constantly (if only the Earth were transparent) with an upskirt vision of their environment.

What David Deutsch seems to be saying (in a roundabout fashion) is that we would do well to consider, in an equally tangible and concrete sense, that we exist within a multiverse where the quantum effects admitted by today's laws of physics must be thought of, not only as possible happenings, but as garden-variety aspects of the fabric of everyday reality. And I'm not sure that many of us are prepared, at present, to assimilate profoundly that weird mode of looking at existence. Between archaic fairy tales (often supported by so-called commonsense) and hard state-of-the-art science, we persist in hoping, if not believing, that there must surely be some kind of convenient "third way out".