The Scientific Secrets of Doctor Who

by Simon Guerrier

  Close to a black hole, the effect would be even greater. In fact, warping of space-time caused by the black hole’s extreme gravity can lead to some very strange effects indeed. As you fell towards a black hole an observer watching you at a safe distance from the event horizon would see time appear to slow down for you. On reaching the event horizon itself, the observer would see you apparently frozen in time. But from your point of view time would seem to pass normally, while events in the rest of the universe appeared to run at an ever increasing rate. If you could somehow pause at the event horizon and look out at the rest of the universe, you’d see all of eternity passing. That’s what seems to happen to Mother of Mine at the end of The Family of Blood (2007): we are told that the Tenth Doctor tricks her into the event horizon of a collapsing galaxy.

  But if you journey past the event horizon, there is no force which could stop your fall – and, as you plummeted ever closer to the singularity, the distorting effects of gravity would become even more pronounced. Once inside the event horizon, the normal directions of space and time become wrenched around. The space direction which was ‘down’ – towards the centre of the hole – becomes the time direction ‘into the future’. Effectively your destiny becomes the singularity at the centre of the black hole and the universe outside the event horizon is forever barred to you, because it’s locked in your personal past. So travelling into a black hole inevitably involves travelling through time, faster and faster into the future – and to escape it you’d need to be able to travel backwards in time into the past.

  In effect, whatever the size of the black hole she was imprisoned in, Mother of Mine wouldn’t feel she was there for very long: time outside would whizz by in an instant as she plummeted to her doom in the singularity. It’s a boggling concept and not easy to comprehend. But if a ship such as the TARDIS could somehow move freely inside the black hole’s gravitational field it would inevitably also travel through time. No wonder the Time Lords are interested in black holes.

  * * *

  ‘You know why this TARDIS is always rattling about the place? … It’s designed to have six pilots, and I have to do it single-handed. … Now we can fly this thing … Like it’s meant to be flown. We’ve got the Torchwood Rift looped around the TARDIS by Mr Smith, and we’re going to fly Planet Earth back home.’

  The Tenth Doctor, Journey’s End (2008)

  * * *

  In The Deadly Assassin (1976), the Doctor reveals that all the power of the Time Lords devolves from the nucleus of a black hole called the Eye of Harmony – though it’s not clear if this is the same black hole as the one in The Three Doctors. According to the Time Lords’ own histories, the Eye of Harmony was created by a Time Lord called Rassilon – not Omega. That might just be the official history leaving out Omega’s role, but whereas we see the black hole in The Three Doctors somewhere out in space, the Eye of Harmony is revealed to exist on the Time Lord home planet, Gallifrey. It’s such an outlandish idea – a black hole being kept on a planet – that other Time Lords don’t believe it.

  Another of the Doctor’s own people – his companion, Romana – is surprised when the Doctor suggests in The Horns of Nimon (1979–1980) that a black hole can be created artificially using a gravity beam to track matter to one point in space, until there’s enough mass pressed together that it collapses to a singularity. It turns out that two artificial black holes have been created, with a hyperspatial tunnel between them. The fact that this is a surprise in the story is important: it suggests that the Doctor and his people don’t fully understand the physics of black holes.

  Yet in the television movie Doctor Who (1996), we learn that the Doctor’s TARDIS is powered by something also called the Eye of Harmony. When opened, this power source has the ability to warp matter so that the Doctor can step through a pane of glass, while later it endangers the whole planet. It’s not stated in the TV movie that this Eye of Harmony is a black hole, but the Eleventh Doctor confirms that in Journey to the Centre of the TARDIS (2013).

  We’re not told if the Eye of Harmony in the Doctor’s TARDIS is the same Eye of Harmony that was on Gallifrey in The Deadly Assassin. Perhaps every TARDIS was somehow linked to the same, single Eye of Harmony, which is still on Gallifrey. However, Gallifrey has been lost since the last day of the Time War (which we’ll discuss more in Chapter 9) – the Doctor thought his home planet had been destroyed before discovering in The Day of the Doctor (2013) that he himself had moved it into a pocket universe. If there was a continuing link between his TARDIS and Gallifrey, surely he would never have believed the planet had been destroyed, and he might even have been able to use that link to make contact again with his people. There would also be no reason for him to refuel the TARDIS with rift energy, as he does in Boom Town (2005).

  So it might be that every TARDIS contains its own unique black hole, each one called an Eye of Harmony. But other Time Lords in The Deadly Assassin and The Horns of Nimon don’t seem to know much about black holes. It would be like people driving cars but not knowing about them having engines or needing petrol.

  That suggests another possibility: some time between The Deadly Assassin and the TV movie, did the Doctor take the one and only Eye of Harmony from where it was kept on Gallifrey and use it as a new power source for his TARDIS? The Doctor tells Rose in The Satan Pit that his people ‘practically invented black holes … Well, in fact, they did.’ But it seems that he’s one of the few Time Lords to know that.

  At least, that’s one theory, deduced from the available evidence. We might learn in a future episode that it’s not right at all – that all TARDISes have black holes for engines, and there’s nothing special about the one in the Doctor’s TARDIS. But that’s the point: we need more and better evidence before we can be sure.

  Science is a series of statements that are revised and sometimes completely overturned when new evidence comes along. As we saw in Chapter 1, the progress of science has often been the result of people puzzling over the bits of evidence that don’t fit the accepted rule: that the position of Mercury doesn’t fit what Newton predicted, for example. Our knowledge is provisional rather than certain.

  We’re still not absolutely certain that Cygnus X-1 is a black hole – it’s just that the evidence available to us so far seems overwhelmingly to fit that idea. But it’s possible that it might turn out to be something else entirely, or that we have to completely revise our ideas about black holes. Time, and better evidence, will tell.

  In fact, a vast amount of the universe remains a complete mystery to us. Just four per cent of the universe is made up of baryonic matter – the atoms that make up galaxies, stars, planets and people, and that we can detect directly. We can deduce that something else is out there: something that does not absorb or emit light (meaning we can’t see it) but that generates enough gravity to affect things around it – just like the footprints of the invisible Visians. This mysterious stuff affects the speed that stars orbit in galaxies and the way galaxies cluster together. We can even deduce that this stuff exists in the halo of our own Milky Way galaxy, and that it makes up twenty-three per cent of everything in the universe. But we currently don’t know exactly what it’s made of – scientists simply refer to it as ‘dark matter’.

  It gets stranger still. Our observations of distant galaxies tell us that the universe is expanding – getting bigger and bigger. This is what we would expect for a universe which began in the tremendous explosion of the Big Bang. But over time we would expect the gravity of the galaxies to act as a brake, pulling against the expansion and slowing it down. Instead astronomers have discovered the opposite – rather than gradually slowing down, the expansion of the universe is actually getting faster and faster as time goes by. So there must be something else in the universe, some kind of invisible force or energy which acts against gravity. Scientists have named this mysterious quantity ‘dark energy’ – and we can deduce that it makes up the remaining seventy-three per cent of the universe – almost three qu
arters of everything out there. Together, dark matter and dark energy make up a whopping ninety-six per cent of everything in the universe – almost all of it! These invisible components help to explain the large-scale structure of the universe we can see, but they also remind us just how little of what’s out there we currently understand.

  In spite of these mysteries – or because of them – we continue to explore the universe with our telescopes and spacecraft, looking for answers, slowly deducing the strange and incredible nature of reality.

  In fact, that’s what really drives the TARDIS – not the black hole it has as an engine, but the attitude of its pilot. Other Time Lords have TARDISes, but the Doctor uses his to explore time and space in search of the weird and wonderful, the stuff he doesn’t already know. It’s this unknown wonder that he offers each of his companions – and so each of us watching his adventures on TV, as well. And that’s why Doctor Who remains so successful even after fifty years: it is powered by curiosity.

  * * *

  Antimatter

  In The Three Doctors, the black hole is the source of an energy beam reaching to the Earth, a bit like the beams of electromagnetic radiation generated by a pulsar. (In fact, scientists think that black holes can also generate jets of matter and energy which are blasted into space.) Journeying along the beam and through the black hole, the Doctors discover a universe composed entirely of antimatter.

  Although scientists don’t know exactly what happens to material once it reaches the singularity inside a black hole, it’s unlikely to be a gateway to a universe of antimatter. But antimatter does exist and is made of particles that have the same mass as ordinary matter but with the opposite electrical charge. For example, normal matter contains electrons which have a negative charge, but in antimatter the role of electrons is taken by similar particles with a positive charge – called ‘positrons’. When matter and antimatter come into contact they destroy each other completely in a tremendous blast of energy – a process known as ‘annihilation’. This process is important to the ending of both The Three Doctors and Arc of Infinity (1983).

  As far as we can tell, our universe is made almost entirely of normal matter. It’s still a bit of a mystery why the universe wasn’t created with equal amounts of matter and antimatter, but perhaps it’s just as well, because it wouldn’t have lasted very long if it had been. However, it’s possible to imagine universes like the ones in The Three Doctors or Planet of Evil (1975), where antimatter dominates over matter.

  Despite its extreme rarity, antimatter is found in our universe, and tiny amounts can even be made artificially in particle accelerators like the Large Hadron Collider at CERN in Geneva. Antimatter particles are also created by natural processes such as lightning strikes and radioactive decay, although with so much normal matter around they don’t usually last long. The extreme physical environments around neutron stars and black holes are also good places to look for antimatter particles and astronomers have detected the characteristic bursts of energy as they annihilate with particles of normal matter. Scientists have speculated that combining matter and antimatter could be a very efficient way of producing large amounts of energy, but the main problem would be collecting enough antimatter to be useful in the first place. So we’re still a long way from understanding antimatter well enough to use it to power spacecraft, as they do in Earthshock (1982).

  * * *

  ‘“Kiss-me-quick-squeeze-me-slowly”?’

  ‘Yes! Hilarious. See?’

  ‘“Kiss. Me. Quick… Squeeze. Me. Slowly.” Nope. Still nothing.’

  ‘It’s just a joke.’

  ‘Is speed of central importance in these actions?’

  Clara fixed the Doctor with a look, which he ignored as he placed the pink shiny metallic hat back down on the TARDIS console without trying it on.

  ‘Fine, change the subject,’ she said with a sigh.

  ‘Shouldn’t it be quickly? Kiss me quickly? Is it funny now?’

  ‘Never mind.’

  ‘Kick me quick. Now I can see how that might work. Kick me quick… appease me slowly.’

  Clara marched across the console room, doing her best to keep calm.

  ‘I just thought you might like to see where I’m from. That’s all. My home. I thought you might like to visit it.’

  Once upon a time, she thought bleakly, you would have. And we’d have had such a wonderful time. And you’d have loved that damn hat.

  ‘A “black pool”. Right. Good things very seldom come out of black pools in my experience. Oozing things do. Scuttling beastie type things.’

  ‘Well, I did.’

  ‘That’s why you scuttle so much.’

  ‘I do not scuttle! I…’

  ‘Flounce?’

  ‘Glide!’ Clara tried again. ‘We’ll go up the tower! See the ballroom! And the illuminations! And I’ll make you eat candyfloss!’

  There was a very long pause. The Doctor’s face was stern. Then he turned round, slowly.

  ‘I love candyfloss.’

  The TARDIS wheezed to a halt. Dressed in a black top and mini-skirt, Clara ran delightedly to the door.

  ‘Home!’ Then she turned round and regarded the Doctor. ‘You’ll have to take that coat off.’

  The Doctor looked up, surprised. ‘Well, I don’t think so.’

  ‘It’s Blackpool. Nobody ever wears a coat.’

  ‘Oh dear. A deal breaker.’ He turned back towards the console display.

  ‘You always get like this when you’re doing something nice,’ shouted Clara cheerily as she headed for the door. ‘I just ignore it. Mind you,’ she went on, almost to herself, ‘Blackpool in November… maybe we can let you off just this once.’

  Then she stepped out of the TARDIS into a steaming hot jungle.

  The vines hung heavy in the trees, which were weighed down with strange brightly coloured fruits. The air was damp and sweet with the scent of rotting vegetation. Underfoot were fallen fronds and burst pomegranates, decaying where they lay.

  ‘Oh no,’ said Clara, looking round, her hands on her hips. ‘This isn’t Blackpool. Stupid TARDIS.’

  The Doctor popped his head out of the door, then glanced back at the console readout. ‘It most certainly is,’ he said as he stepped out into the lush green landscape. ‘Oh, it’s lovely! You should have said!’

  ‘No!’ said Clara. ‘This is a jungle! Blackpool has a Ferris wheel. And a beach! And…’ She looked up. Overhead, the great wrought iron structure of the Blackpool Tower was slightly tilted. It had oxidised, and great vines twisted their way through the gaping holes in its structure. Brightly coloured birds swooped round the top. In front of them was what remained of the Golden Mile. Smashed lightbulbs crunched underfoot from the ruined illuminations; the promenade was completely overgrown, and high black waves lapped right across the cracked tramlines. In the distance, through the broken-down struts of the Big One rollercoaster, she saw, stilting along awkwardly –

  ‘…giraffes?’ Clara whipped round to face the Doctor. ‘Giraffes? What’s happened to my hometown?’

  The Doctor took out his pocket watch. ‘Oh. Yeah. Bit late.’

  She glanced at the writhing greenery. ‘Is this the trees doing a thing again?’

  The Doctor shook his head sadly. ‘’Fraid not. This is here to stay. It’s 2089. It’s climate change. The real deal. Looks like all those Bags for Life you bought didn’t quite do the trick.’

  Clara stepped forward, horrified. ‘The Golden Mile, the sand… it was already eroding in my time, you could see it. But they built these sea defences…’ She looked at them. The concrete barriers were overwhelmed with water; crumbled away.

  Horrified, Clara started to run down the promenade, broken glass crunching under her feet. The pier sagged heavily into the high seas, bent and twisted into cruel shapes, dripping vines. Past the pier, a spit of black sand remained, in front of the ruins of the fish and chip shops; upturned plastic ice cream bins bobbing up and down in the water; a s
hipwrecked tram. She stopped and stared, mouth open.

  Hurtling across the sand at full pelt, their heads and manes tossing in the warm wind, their hooves galloping in the rushing water, was a herd of wild donkeys. They looked beautiful and strange, outlined against the dark seas.

  Clara’s hand went to her mouth.

  The Doctor came over, casually eating a handful of grapes that stained his mouth. ‘This place is amazing… What?’

  ‘The donkeys! They’re running wild!’

  ‘Beautiful…’

  As they watched the animals gambolling in the surf, suddenly, as if out of nowhere, came a flashing, buzzing noise. A jagged silver disc, smaller than a frisbee, zipped through the sky, and embedded itself in the side of one of the donkeys, which immediately whinnied in distress and collapsed on the beach.

  ‘Oh no!’

  Clara darted across the sand towards it, as the herd left the creature behind. The wounded animal was tossing and writhing in pain, and she couldn’t get close for the thrashing hooves.

  ‘That projectile was about the size of a CD,’ said the Doctor, coming up behind her. ‘I wonder what it was. Simply Red? I mean, I can understand the urge to throw…’

  The donkey was grunting and screeching as the Doctor moved closer, his face taking on an expression, Clara thought, rather gentler than the one he habitually wore when dealing with creatures on two legs.

  ‘Sssh,’ he said. He knelt down away from the animal’s pistoning limbs, and put both hands either side of the donkey’s head.

  The flailing, terrified creature was immediately soothed at his touch, and quietened its terrible keening and thrashing.