An eccentric fusion of quantum theory, Philip K. Dick and Herman Melville, Mobius Dick is a “many worlds” thriller with a wry sense of humour and a mind-warping plot. Middle-aged physicist John Ringer finds his grasp of reality quickly slipping away after he receives a series of incomplete text messages beginning “CALL ME. H”. The “H” he assumes to be his lost love, Helen, whom he hasn’t seen for the best part of two decades; nevertheless, her inferred presence begins to grow on his horizon, and starts to assume the characteristics of a minor obsession. Ringer is asked, by a former student now heading a research facility in Scotland, to give technical advice to some financial backers on the viability of creating a quantum computer – basically a superfast computer which carries out an infinitely large number of calculations simultaneously in an infinite number of parallel universes. Having nothing better to do Ringer takes the trip, but in the village near the research facility he’s amazed to run into none other than Helen – or rather a woman who resembles her almost exactly, and whose life history corresponds with hers to an uncanny degree, but who in all other respects is a stranger. Questioning her, Ringer learns she’s an investigative journalist doing a piece on the very facility he’s due to visit himself and, still part-convinced she really is his beloved, agrees to help her dig for information.

Complicating things still further, alternating chapters appear to describe a totally different England, one the Germans successfully invaded during WW2; a Communist revolt has since ousted the occupiers, and installed a CP PM in Number 10. In this reality, our hero is an amnesiac named Harry, who awakens in a strange hospital to learn he’s been in some sort of road accident and now can’t remember anything about the world in which he finds himself. A helpful lady psychiatrist informs him his condition is not unique – increasingly large numbers of fellow sufferers are also finding themselves losing their memories, and capable only of recalling details from an imaginary counter-reality which, of course, could not exist. Not only that, but a certain Erwin Schrödinger – a key figure in quantum physics in “our” reality, whose famous wave equation revolutionised modern thought on the subject – never made that theoretical breakthrough in this alternative realm… Some of these alternating chapters take the form of excerpts from a novel about Schrödinger, in which the author fancifully imagines the physicist’s real-life visit to a sanatorium in the 1920s (where one of the resident trick-cyclists, an unpleasant proto-Nazi given to sexually abusing his star patient – a strangely ethereal young woman who may be able to travel between dimensions – later, we infer, goes on to replace Hitler as Führer).

Ringer eventually learns that the quantum computer has already been brought on-line, thus creating a gigantic paradox in which all possible alternative worlds have come into existence at once. Quantum theory holds that our perceived reality is created by a collapsing wave function, created by the act of observation, causing all probabilities to collapse into a single “objective” reality. But the quantum computer is preventing the wave function from collapsing, thus preserving every permutation of possible worlds – and turning the thing off might be even more dangerous than leaving it on…

Awkwardly punning title aside, Mobius Dick rarely puts a foot wrong. It’s engagingly written, highly imaginative and, at times, deeply alarming. Crumey (a theoretical physicist himself) writes in an amusing, uncluttered style, and while neophyte readers may not emerge with a full comprehension of quantum theory, they will grasp enough to chill their marrows. (Quantum computer inventors, take note: if you don’t fully understand how your machine will work, please don’t switch it on. Thank you.) In its cross-contamination of alternative realities, Mobius Dick channels something of the paranoia of that other Dick, Philip K., especially his award-winning Man in the High Castle (1960); though it never mentions Bohr or Schrödinger, that novel too deals in quantum unrest, describing a world where an Axis-controlled alternative present has superimposed itself over the “real” 1960. Reality, Dick seems to say, is a shared delusion – an unspoken consensus of subjective perceptions, collectively describing the world we inhabit. Once that consensus is threatened, who knows what ideas might start to creep through? Dick’s vision, of course, was that of a philosopher, not a physicist; still, he and Crumey are not poles apart. They may come at the topic from different angles, but they agree on this point: that reality is a fragile fabric, all-too-easily torn.