PD Smith

Much Too Difficult For Us

Times Literary Supplement, 18 May 2012, p 29

Build Your Own Time Machine: The Real Science of Time Travel, by Brian Clegg (Duckworth), 311 + vii pp. Duckworth. £14.99. ISBN: 978-0715642900

Review by P. D. Smith


“Time,” said Borges, “is the one essential mystery.” Borges loved the subversiveness of time in HG Wells’s The Time Machine (1895) and Brian Clegg’s exploration of time and time travel begins, albeit briefly, with Wells’s fictional journey into the fourth dimension.

Of course, in one sense we are all time travellers. We move forwards at the rate of one second per second. And we can also travel back in time through our memories, the favoured medium of another fictional time traveller, Van Veen, Nabokov’s “epicure of duration” in Ada or Ardor (1969). But unfortunately, despite the sci-fi cover of his book, Clegg is not especially interested in either memory or fictional treatments of time travel. Instead, he has written a detailed account of the science of time travel, for as he says at the outset, “there is no physical law that prevents time travel”. In principle, the fantasies of Wells might just be possible, although as Clegg makes clear, the practical and engineering problems are immense.

He begins, as all studies of modern physics must, with Einstein and relativity. Throughout this book the science is described with clarity and even elegance. Einstein’s theories provide the conceptual rules for what is or is not possible as regards travel through the fourth dimension. The mathematics of special relativity (1905) show that if you were to travel faster than light then you would be moving backwards in time: “if it becomes possible to go fast enough, the result can be a reversal of the flow of time”. Einstein’s later theory of general relativity also introduced the idea that space-time itself could be warped: “Gravity has an impact on time as well as on space.” Both special and general relativity therefore offer theoretical possibilities for manipulating time.

On 7 May 2005, a rather special event was held at the Massachusetts Institute of Technology. It was a welcoming party for time travellers. A stage was set up in a courtyard and theatrical smoke released to create the right atmosphere of suspenseful anticipation. It was a clever idea. An event such as this, which had been widely advertised and reported (effectively sending an invitation into the future), would provide an ideal opportunity for any future time travellers to reveal themselves. Unfortunately no one from the future turned up. For Stephen Hawking this is evidence that time travel is not possible. Clegg disagrees. He makes the intriguing point that time travel mechanisms based on relativity cannot send anything back before the moment at which they were switched on. Therefore, as no one has yet invented a time travel machine, we would not expect to see visitors from the future. But he qualifies this, saying that it does not preclude the possibility that unknown alien civilizations may have already invented time-travel technology. And, he adds, if they are advanced enough to voyage into the fourth dimension, it is possible that they may also have mastered the art and science of remaining invisible.

Fantastic though these suggestions sound, Clegg never fails to highlight the practical difficulties of time travel. He uses the famous twins paradox, a thought experiment derived from relativity, to illustrate some of these. According to this, if one of the twins remains on Earth while the other travels away in a space ship at extremely high speeds, the effects of both time dilation due to the high speeds and the acceleration cause them to age differently. As Van Veen puts it in his study of The Texture of Time, “the galactonaut and his domestic animals, after touring the speed spas of Space, would return younger than if they had stayed at home all the time.”

But although the scientific concepts sound (relatively) simple, the application of the science to achieve time travel is challenging, to say the least. Clegg calculates you would need 10 billion times the amount of energy produced by every power station in the US running for 250 years in order to push a space-shuttle-sized craft up to 90 per cent of the speed of light. And, of course, according to relativity the faster something goes the more its mass increases. So in fact you would need vastly more power – perhaps the equivalent of 800 or so years of power generation. And even then it would take eight years to travel a mere eleven years into the future.

Despite the title, the lesson of Build Your Own Time Machine seems to be that no one will be doing so any time soon. Clegg sets up elegant and fascinating theoretical possibilities for time travel only to show that the practical difficulties are virtually insurmountable. The options for potential time travellers include cutting up a neutron star to build a vehicle made of neutron star material whose gravitational field slows time; quantum entanglement (described by Einstein as “spooky action at a distance”) which enables small-scale teleportation; and Gödel’s proposal of a rotating universe in which space-time is curved, making it theoretically possible to loop back in time.

The longest chapter in the book (“Alice through the wormhole”) considers the truly mind-boggling physics of black and even white holes, the latter described as “a black hole that runs backward in time…a singularity of creation rather than of destruction”. Theoretically, two white holes back to back in space might create a wormhole, a shortcut through space and, indeed, through time, because you would travel through it at speeds faster than light. The renowned physicist and futurologist Michio Kaku has even designed a time machine based on this idea. Clegg remains distinctly sceptical, however, and even Kaku admits: “This is for a very advanced civilization, not for us.”

Clegg proves himself to be a lucid guide to the often complex science of time travel. His ambitious book covers more or less the whole of twentieth-century physics from relativity to string theory and at times his obvious pleasure at explaining each and every esoteric theory threatens to obscure the book’s true subject (some careless biographical errors have crept into his narrative as well: for instance, the young Einstein stayed in Switzerland with the Winteler family not the “Wintlers”; the friend who helped him with his mathematics while an undergraduate was Marcel Grossmann, not “Grossman”; and his second wife Elsa Löwenthal, née Einstein, was rather more than a “friend” when she met him: she was his cousin). But, as Clegg says, the idea of time travel does indeed provide a “delight that the feats of no other near-possible technologies bring.” Just don’t expect to be jumping into your DeLorean time machine in the near future.

[N.B. This may differ from the version printed in the TLS.]