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.

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David Olusoga's look at a forgotten history shows there's always been black in the Union Jack

Black and British: A Forgotten History addresses one of the greatest silences in British historiography.

Nineteen eighty-four was a transformative year for David Olusoga. Then a young teenager, he was driven out of his council home, together with his grandmother, mother, two sisters and younger brother, by a sustained campaign of nightly stoning of their windows. When Olusoga recalled the experience before television cameras last year, he wept. His book is a product of that childhood terror, and partly an exploration of his condition as a black Briton. As he states, “The oral history of 20th-century racial violence has never been collected or collated, but it is there and it is shocking.”

Nineteen eighty-four affected him in another way: the publication of Peter Fryer’s groundbreaking Staying Power: The History of Black People in Britain introduced him to the scholarship needed to understand his position in Britain. Fryer’s book was monumental, inspiring conferences, publications, the setting up of local history groups, the establishment of Black History Month, and radio and television programmes. It began to alter (slightly) the history curriculum at university level: the first undergraduate one-year course on black British history and culture was taught at the University of Warwick in 1984. It was an apt university to experiment with such developments, since Lord Scarman, who reported on the Brixton riots of 1981, was its chancellor.

Olusoga patterns his narrative after Fryer’s, starting with the North African presence in Roman Britain. He updates Fryer, citing radioisotope analysis of skeletons and craniometrics, which support written documentation of Aurelian Moors guarding Hadrian’s Wall and settling in places such as Yorkshire. Indeed, third-century York may have been more ethnically and racially diverse than present-day York. Roman writers such as Pliny who chronicled – or rather fabricated – African life shaped perceptions of a continent populated by anthropophagi and other fantastic creatures, half-human, half-animal. John Mandeville, whose travelogue (circa 1356) was one of the most widely translated books of the later Middle Ages, presented Africans as naked savages living amid heaps of gold to which they gave no value.

And so, equipped with the fruits of Islamic learning (new navigational instruments, books on astronomy and trigonometry), European explorers set sail for Africa to relieve the natives of their gold. Pope Nicholas V gave his blessing, so long as the Vatican benefited. In the 15th and 16th centuries, thousands of pounds of gold were shipped to Europe. But slaves were more valuable, so the British fought the Spanish for a share in the trade and eventually came to dominate it. At the Treaty of Utrecht in 1713, Britain was granted the right to supply slaves to the Spanish colonies in the Americas, a right then passed on to the South Sea Company. The “South Sea bubble”, the greatest financial crash of the 18th century, was intimately connected to Britain’s dealings with Africa, though this is rarely acknowledged by historians.

The Royal African Company, established by Charles II in 1672, eventually enslaved and transported more Africans than any other company in British history. It built slave forts on the African coast, some such as Bunce Island in Sierra Leone furnished with a “rape house”. Separated from home and family and landed in the West Indies (countless numbers dying of suffocation during the journey, given that the people traffickers were packing the holds to maximise profits), the Africans had no recourse to the law, much less the conscience of their captors. The Barbados slave code of 1661 stripped Africans of all human rights, and set out ways in which they were to be punished, to exert control over their labour (mutilation of the face, slitting of nostrils, castration, execution). After decades of complaints, the Royal African Company lost its monopoly in 1712 and, Olusoga writes, “Independent traders were turned loose upon the shores of Africa.” These traders had argued (“stone-blind to irony”) that the right to enslave Africans was “a defining feature of English freedom” and that the Royal African Company had breached their status as free-born Englishmen. Eventually, 11,000 separate British slave-trading expeditions resulted in the trafficking of three-and-a-half-million Africans to the New World plantations, the greatest forced migration in modern history until the 20th century.

How could Britain, a civilised and Christian nation, indulge in rape, torture, killing and the forced labour of Africans over two centuries? The answer is money. If you had spare cash or could borrow, investment in slavery was a sure winner, never mind slave rebellions or hurricanes that destroyed cane fields. Sugar was king: originally a luxury, it became one of the main sources of calories for the British poor. And so many hundreds of thousands of British workers were directly dependent on slavery (from sailors to those who built, rigged and repaired ships) that it was easy to turn a blind eye to the inhumanity. Once insignificant villages, great cities such as Liverpool, Bristol and Glasgow sprang up on the profits of slavery.

But a group of 12 disciples of Christ set out to change things. In 1787, they met in London and set up the Society for Effecting the Abolition of the Slave Trade. They included Josiah Wedgwood (the pottery entrepreneur), Granville Sharp and Thomas Clarkson. Fired by religious feeling, they embarked on a campaign of public education and political lobbying “unprecedented in scale and revolutionary in nature”. Supported by African authors of slave narratives such as Olaudah Equiano and Ottabah Cugoano, they held meetings all over the country, attracting huge crowds. Thousands of petitions were presented to parliament. Women, denied a meaningful role in politics, formed their own organisations, writing tracts, pamphlets and poems, gathering signatures for petitions and fundraising: “At certain times and in certain places they were the engine room of the movement.”

Abolition was the first mass philanthropic movement in Britain, and it ended the slave trade in 1807. It could have ended earlier, but the planter interests in parliament defeated William Wilberforce’s attempts. In 1796, a bill was defeated by only four votes: a group of abolitionist MPs went to the opera and missed the vote. Between that night at the opera and 1807, nearly 800,000 Africans were enslaved.

Women such as Elizabeth Heyrick continued to lobby for the abolition of slavery. They organised a boycott of sugar, produced more petitions and hosted meetings. It was such a brilliantly organised programme of mass protest that slavery was declared abolished in 1833: 46,000 slave owners were given £20m in compensation (£17bn in today’s money), the largest payout in British history and 40 per cent of all government spending that year. The enslaved Africans had to wait another five years for their freedom and were not given a penny.

Long after slavery ended in the British colonies, British people continued to lobby the American government to free their slaves. The many African-American abolitionists, such as Frederick Douglass, who visited Britain from the 1840s onwards, were well received and, again, thousands of people greeted them and raised money to support their cause.

The publication in 1852 of Uncle Tom’s Cabin, by the American abolitionist Harriet Beecher Stowe, swelled national sympathy for the plight of black slaves. More than a million copies were sold in Britain – cheap pirated versions reached a mass readership. The novel became the bestselling book of 19th-century Britain; it was adapted for the theatre and generated mass-produced merchandise – playing cards, jigsaws, tableware. Its extraordinary success rested upon the “foundation of sympathy… laid down during the previous 70 years of abolitionist activity in Britain”.

Yet American slave-produced raw cotton continued to feed the 4,500 mills of Lancashire. In 1860, cotton goods accounted for 40 per cent of all British exports. In 1861, the Economist stated that nearly four million people in Britain depended – directly and indirectly – on the cotton industry; a fifth of the entire population. When the American Civil War interrupted the supply of cotton, hundreds of thousands of British workers were made destitute, dependent on soup kitchens, and the British economy was “dealt a thunderous blow, all because an ocean away the forced labour of four million enslaved black Americans had been disrupted”. Needless to say, the national mood changed. The masses who once supported black freedom now campaigned for the Deep South.

Olusoga brilliantly reveals such contradictions in British society. In dealing with the black contribution to the First World War, for example, he cites popular gratitude and admiration for black Britons – among them Walter Tull, who fought on the Western Front. Tull played professional football for Northampton but instead of signing up for Glasgow Rangers, he enlisted. Rapidly promoted to sergeant, then second lieutenant, he led white British troops into action and died in 1918, having been mentioned in despatches and recommended for the Military Cross. And yet Africans and West Indians were banned from the victory parade in 1919. Anti-black riots broke out in Liverpool that year.

During the Second World War, thousands of black American soldiers stationed in Britain were befriended by white Britons who opposed efforts by the white military to segregate them. West Indians fought with the Allies – more than a hundred were decorated. And yet anti-black race riots broke out in 1948 in Liverpool and in 1958 in Nottingham and London’s Notting Hill. The following decades were taken up with popular and political rhetoric about immigration and parliamentary acts to limit blacks coming to Britain.

Olusoga’s stated purpose is to argue that black British history is not about migration and settlement, whether of black servants in the 18th century or black workers in the Windrush era. It is about the centuries-long engagement with Africa, a consequence of which is the black presence in Britain. Olusoga has benefited from and added significantly to the work of Fryer and other historians such as James Walvin. He has discovered new and exciting research materials in African archives, among them the Register of Liberated Africans in Sierra Leone, which list names, bodily details, ethnicity and origins, thus putting a human face on people otherwise treated as fodder and statistics. Such sources give his writing freshness, originality and compassion.

Like Fryer’s book, Olusoga’s will inspire and will come to be seen as a major effort to address one of the greatest silences in British historiography.

Black and British: A Forgotten History
David Olusoga
Macmillan, 624pp, £25

David Dabydeen is a novelist, broadcaster, academic and co-editor of “The Oxford Companion to Black British History” (Oxford University Press)

This article first appeared in the 17 August 2017 issue of the New Statesman, Trump goes nuclear