How much of “Doctor Who” might really be possible?

Science shows why Doctor Who is so special.

As Doctor Who’s 50th anniversary looms, time travel is everywhere – on the screen, at least. Famously, the Doctor can whizz through the years using a “dimensionally transcendental” machine, the TARDIS, and make changes to the past as and when he likes. But what is time travel – and how much of “Doctor Who” might really be possible?

A handy definition of time travel comes from philosopher David Lewis. Lewis says time travel involves a journey having different durations viewed from outside (in “external time”) or from inside (in “personal time”). Suppose you spend five minutes travelling aboard your machine, as measured by (e.g.) your watch and your memories. On arrival, you find 150 years have elapsed in the outside world. Congratulations, you have time-travelled. Five minutes of your personal time has covered 150 years of external time.

Odd as this sounds, Einstein’s theory of Special Relativity introduced such possibilities to physics in 1905. The theory says: the duration of a process varies with the relative velocity of the observer. The closer that relative velocity gets to the speed of light, the longer the travelling process takes.

Suppose you want to see the Earth a billion years hence, but worry you have only about 50 personal years left. Special Relativity specifies that if you travel very close to the speed of light relative to the Earth, your 50 personal years can cover one billion Earth years.

In backward time travel, personal and external time differ in direction, so journeys end in external time before, not after, they begin; you spend five personal minutes travelling 150 years into the external past. General Relativity suggests that the universe is essentially curved spacetime, which might allow such divergences of external and personal time.

Relativity treats space and time as aspects of a single entity: “spacetime”. One of the more remarkable features of General Relativity is that it allows time and space axes to be interchanged, so one observer’s space axis can be another observer’s time axis.

In 1949, Austrian mathematician Kurt Gödel used General Relativity to describe a universe where intrepid voyagers can go anywhere in (past or future) time without travelling faster than light. Gödel’s universe has no boundaries in space or time, and all the matter in it rotates. But our finite, non-rotating universe is not Gödel’s. Despair not though – simply spin an ultradense, very (maybe infinitely) long cylinder very fast. Spacetime should curve around the cylinder so the direction of the local future partially points into the external past. Such devices are called “Tipler Cylinders”, after physicist Frank Tipler.

Better yet, quantum theory suggests that “wormhole” connections between different spacetime points spontaneously form and break all the time. The chances are that natural wormholes are tiny - vastly smaller even than an electron, (and a billion trillion electrons can fit in a teaspoon). But you could perhaps find (or create) a wormhole big enough and durable enough to let you slip through into the past. Difficult, but theoretically possible.

No, you can’t kill your physics teacher

So perhaps you could travel into the past. But what about paradoxes? What is to stop you assassinating your grandfather or yourself as infants? One answer says: logical consistency.

Classical logic says you cannot consistently kill in infancy someone who achieves adulthood. But, Lewis says, time travel need not involve doing the logically impossible – provided travellers’ actions in the past are consistent with the history whence they come. So you could try killing your baby grandfather, but something would foil you – you would sneeze, or your gun would jam. Lewisian time travel is therefore (classically) consistent, but might look very strange, since seemingly possible actions (like shooting an unprotected infant) would prove impossible.

Another view says that backward time travel requires many worlds – that is, many different but equally real versions of physical reality. Physicist David Deutsch and philosopher Michael Lockwood argue that time travel must involve inter-world travel. If you travel backwards in time, you must arrive in a history different from your native one and so would be quite unfettered by your past once you get there. You could even kill this other history’s counterparts of your grandfather and yourself.

Both these concepts of backwards time travel may disappoint anyone wanting to change the “one and only” past. Conventional logic says time travellers would either help make history what it was (Lewis) or create a different history (Deutsch/Lockwood). However, quantum logic might let travellers change the actual (one-and-only) past.

Suppose we hold that quantum measurements determine (or change) quantities measured, even if those quantities lie in the past. Someone could travel back and “observe” history turning out differently from how it originally was, thereby retrospectively making actuality different from what it had been. What would happen to travellers who rebooted history is not clear, but this model seems closer to the time travel familiar from “Doctor Who” and other fictions. Beware, though, because quantum theory allows no predicting, and still less controlling, of the outcomes of changing the past. There would be no way to foresee the effect you would have on the present.

So classical logic, General Relativity and quantum theory all seem to permit time travel. Classical logic plus General Relativity suggest backward travellers face weird consistency constraints. Many-worlds travellers face no constraints, but get displaced into different histories. Quantum-logic travellers could change the (one and only) past without constraints, but they couldn’t predict or control what they would get.

So far, however, it seems only the Doctor knows how to change the past at will.

Alasdair Richmond received funding from the Arts and Humanities Research Council, to fund one semester of a two-semester leave period that covered the academic year 2008-2009.

The Conversation

This article was originally published at The Conversation. Read the original article.

The eleven incarnations of the Doctor. Image: BBC/Matt Burlem

Alasdair Richmond is a Senior Lecturer in Philosophy at the University of Edinburgh.

NICOLA TYSON, COURTESY SADIE COLES HQ, LONDON
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Dave Haslam's history of venues makes nightclub walls talk

Life After Dark: a History of British Nightclubs and Music Venues reveals the ghosts of hedonism past.

“If these walls could talk . . .” The cliché owes its force to the notion that buildings are sentient – the suggestion that what happens inside them leaves a trace element. We feel the power of this idea in very different ways as we tour, say, Versailles or Dachau. It’s an idea very much at play in the best passages of this book.

There is a wonderful moment early on when the author tours the Dean Street Townhouse building in Soho, central London, along with a few young members of staff. The location is now an upscale hotel and restaurant but, as Haslam explains to them, back in 1978 the basement hosted Billy’s nightclub. Billy’s was run by Steve Strange and played host to the burgeoning New Romantic movement, with the likes of Boy George and Spandau Ballet all trooping down the steps off Meard Street. Later on, in 1982, the ultra-hip original Goth club the Batcave opened its doors on the top floor of the same building, and the elevator would have ferried the likes of Robert Smith of the Cure and Marc Almond skywards.

The twentysomething staff don’t seem altogether sure who these people are, but Haslam goes further as he tells them (no doubt to further head-scratching) that the building has in fact been a nightclub since the 1920s, when it was called the Gargoyle. The people who danced and partied there over the decades would have included Henri Matisse, Tallulah Bankhead, Fred Astaire and Noël Coward, he says.

It is a fantastic example of the deep vein of hedonism you sense thrumming behind the walls of many buildings in such areas as Soho, and Haslam extends this approach throughout the book as he travels across Britain, digging into the history of the likes of the Leadmill in Sheffield, the Barrowland Ballroom in Glasgow, the Cavern in Liverpool and the Free Trade Hall in Manchester, often tracing the origins of the venues back to Victorian times. It makes for a fascinating read, especially if you have ever stood in an old music venue and wondered (as I have often done) about the many previous generations whose fights, fashions, frugs and frocks have played out on the very boards you are treading.

Along the way, there are in-depth, illuminating interviews with figures as diverse as the novelist David Peace (on Goth clubs in Leeds) and James Barton, the co-founder of Cream (on the problems of running a nightclub in a city rife with gang warfare), as well as less familiar names such as Hyeonje Oh, the current owner of the Surakhan restaurant on Park Row in Bristol. Haslam explains to the amiable Mr Oh (in a wonderful scene reminiscent of that visit to Dean Street Townhouse) that, back in the mid-Eighties, the basement of his restaurant played host to the Dug Out club, where the careers of Massive Attack and Nellee Hooper began. None of this means very much to the restaurateur, until Haslam points out that Nellee Hooper has worked with Madonna. Mr Oh has heard of Madonna.

On occasion, the book slides into potted histories of the youth movements that came out of the nightclubs it is documenting. So we get a few pages on the emergence of punk rock, a few pages on the rise of acid house – nothing, frankly, that anyone with a passing interest in music or youth culture wouldn’t already know. I’m not sure we need to hear again that “one of the people energised by the Sex Pistols [at the Manchester Free Trade Hall] was Tony Wilson, who arranged for the band to premiere their ‘Anarchy in the UK’ single . . . on his Granada TV show”, except in a book aimed at the most general reader (which a book with the subtitle of this one surely is not).

Haslam is on much more interesting ground in the basement of a Korean restaurant that once throbbed to the heavy dub reggae whose influence shaped a generation of music performers and producers. Or when he describes the progress of the Coliseum in Harlesden, north-west London, from cinema in 1915, to fleapit punk rock venue in the Seventies – where, in March 1977, you could have seen the Clash (along with three other bands, and a couple of kung fu films) for £1.50 – to the Wetherspoons pub that stands on its site today. In these pages he asks you to imagine Daddy G of Massive Attack working the decks where the crates of produce are now stacked, to see Joe Strummer’s right leg pumping just inches from where office workers now sip discounted Sauvignon. In these pages, he makes the walls talk.

John Niven is the author of the novels “Kill Your Friends” (Windmill Books) and “The Sunshine Cruise Company” (William Heinemann)

Life After Dark: a History of British Nightclubs and Music Venues by Dave Haslam is published by Simon & Schuster (480pp, £20)

This article first appeared in the 05 February 2015 issue of the New Statesman, Putin's war