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.

BBC/ ITV Cradle Ltd/Matt Squire
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Is Danny Baker a “bona fide genius”? Not in his new show

The clichéd decade: Cradle to Grave and Danny and the Human Zoo reviewed.

I’m not qualified to rule on whether or not Danny Baker is, as the newspapers insist, a “bona fide genius”; I gave up listening to the ever more blokeish BBC Radio 5 Live a while ago, and I’m too young to remember the supposedly fantastic pieces he delivered to the NME back in the day (I read that they were even more amazing than those of Tony Parsons, which is saying something, isn’t it?). But I can tell you this: his new autobiographical comedy series, Cradle to Grave (Thursdays, BBC2, 9pm), displays no evidence at all of his talents, brilliant or otherwise. Anecdotes that just peter out. Jokes that fail to hit home. Misplaced nostalgia. Honestly, what’s the point? If you want 1974 – and quite a lot of us seem to, if the performance of Jeremy Corbyn is anything to judge by – you’d be better off treating yourself to a box set of the eternally satisfying Whatever Happened to the Likely Lads?.

The series, co-written with Jeff Pope, is based on Baker’s memoir Going to Sea in a Sieve. It’s 1974, and Danny (Laurie Kynaston) is a randy teenager who still lives at home in good old Bermondsey with his ducking and diving docker dad, Fred, aka Spud (Peter Kay), his kindly mum, Bet (Lucy Speed), and his older sister, Sharon (Alice Sykes). A voice-over tells us, in effect, to forget all about the nasty old three-day week and to consider instead the warmth of lovely south-east London. How decent its people are, how eager to try out newfangled consumer goods such as the continental quilts Spud has pilfered and which now fill the hall of his tiny house like clouds. (Correct: he’s basically Del Boy, minus the Robin Reliant, the cocktail bar and, fatally, the workmanlike jokes.)

The denizens of Bermondsey are not, you understand, quite ready for the new world. In this part of London, bomb sites remain, merrily sprouting buddleia and pink willow herb; men are men and women are women. Spud is horrified to discover that his daughter’s new boyfriend wears – wait for it – white plimsolls, though not quite so horrified as Danny is to find a stranger’s ­penis flapping exuberantly against his cheek when he goes up west to see Hair (needless to say, our Danny was in search of naked girls, not sweaty blokes). If you find this kind of thing funny and (I can hardly bear to write the words) “heart-warming”, then you have seven weeks of bliss ahead. Who knows? Perhaps the characters will go on to debate the virtues of the various flavours of Old English Spangles. But I can’t believe that many people will be so easily pleased. Those who are old enough to remember the Seventies will know that the best of the decade’s own comedy was ten times more sophisticated than this, and those who aren’t – those who have never had anything other than a duvet on their bed, and can locate a naked female or even a flapping male member with just one tap of their mobile – will simply watch something altogether more grown-up on Netflix.

Kascion Franklin (centre) on BBC1. Photo: BBC/RED

Unfathomable BBC scheduling (is it having some kind of John Whittingdale-induced nervous breakdown?) treated us to two doses of 1974 as the summer limped to an end. The second loving spoonful came in the form of Danny and the Human Zoo (31 August, BBC1, 9pm), an almost-biopic drama in which Lenny Henry told the story of his painful start in comedy.

My TV critic colleagues have all been most respectful but, lovely as Kascion Franklin’s performance in the lead role was, I couldn’t altogether get with the show. Unlike Baker, Henry certainly wiped the Vaseline from the lens: his version of the Seventies was clear-eyed, particularly in the matter of racism. But his tendency as a writer is to tell rather than show, which becomes wearying, and the narrative he offered us – success on the New Faces talent show, followed by the self-loathing that came of joining the Black and White Minstrels – wasn’t exactly unfamiliar. An unscrupulous manager with bad hair; parents who think their son should get a “proper” job but are secretly oh-so-proud; Mud’s “Tiger Feet” and Alice Cooper’s “School’s Out” on the soundtrack: such TV clichés really should be illegal by now.

Rachel Cooke trained as a reporter on The Sunday Times. She is now a writer at The Observer. In the 2006 British Press Awards, she was named Interviewer of the Year.

This article first appeared in the 03 September 2015 issue of the New Statesman, Pope of the masses