The Scientific Secrets of Doctor Who

by Simon Guerrier

  ‘He’s right,’ said Keinholz. ‘Temperature dropping below ice-point.’ As he spoke, his breath clouded in the air.

  ‘Good, good.’ The Doctor checked the readouts at Keinholz’s workstation. ‘We have to convince them this ship is just a derelict lump of junk, floating in space.’

  ‘And then what?’ said Ferrier frostily, rubbing her arms for warmth. ‘They’ll just become dormant, stuck to the hull. We won’t be able to turn the engines back on.;

  ‘You will,’ said the Doctor. ‘Someone just has to make them a better offer.’ He strolled over to the rear doors, buzzed his pen-shaped device, and they slid open.

  ‘Where are you going?’ asked Locklear.

  The Doctor paused in the doorway. ‘The TARDIS. My wheels. You can come along if you like.’

  Locklear stood in the TARDIS control room, gazing open-mouthed at the high, curved walls pulsing with green light. She’d never seen anything like it before in her life.

  The Doctor darted around the central console, flicking switches embedded in its coral-encrusted surface. As he did, jets of steam hissed out of vents in the floor. He grinned the most manic of grins. ‘Nearly there!’

  There was a stomach-churning rumble and the central glass pillar of the console began to rise and fall. Then the rumbling stopped with a crunch. The Doctor slammed down a lever and sprinted over to the exterior doors. He pulled them open in a grand gesture to reveal the Godspeed floating through space a short distance away.

  Locklear approached the doorway warily. ‘I’m guessing there’s some sort of force field preventing us being sucked out?’

  ‘You guess correct. I can see why they made you captain.’

  Locklear nodded dumbly and peered outside. She could just about make out the barnacles covering the Godspeed’s hull. ‘So how do we lure them away?’

  The Doctor dashed back to the console. ‘Power, Captain Locklear. Power!’

  A few moments later, out in the darkness of space, the lamp on the top of the TARDIS started to flash. It sent out a dazzling, swirling beam of light, like a lighthouse, on and off, picking out the barnacles on the hull of the Godspeed.

  Very gradually, a couple of the barnacles detached themselves from the hull and began to swim through the vacuum towards the TARDIS. Then a few more barnacles detached themselves and followed. Then the entire encrusted body crumbled away as the whole mass of barnacles released the ship and swarmed slowly towards the police box.

  The Doctor stood in the doorway, waving the creatures towards him. ‘That’s it! Come to Daddy!’ Then he smiled and slammed the doors shut.

  The first of the barnacles settled upon the wooden panelling of the TARDIS and its slanting roof. Then more arrived, clinging to the sides, the roof and the underside, burying it in a tightly clustered mass of shells. Then more barnacles covered those barnacles, until not a glimpse of the police box remained.

  In the TARDIS, a warning alarm hooted and the engines made a low grinding sound. The Doctor checked the monitor, which showed a series of revolving circles. ‘Yes, I think I’ve got them all. They’re tucking in, happy as Larry.’

  ‘But won’t that mean you’ll be stuck here?’ said Locklear. ‘They’ll be drawing power from this… ship?’

  ‘Oh, the TARDIS has plenty of welly, don’t worry about that,’ said the Doctor proudly. An instant later, the lights went out.

  ‘You were saying?’ said Locklear.

  The Doctor dashed around the console, adjusting switches by the light of the glowing central column. ‘OK, we’re gonna have to be quick, they’re breeding like, well, like barnacles.’ The controls didn’t respond, so the Doctor pulled a hammer out from under the console and whacked it. Part of the panel exploded into sparks, but the central column started moving up and down.

  The Doctor laughed. ‘First we dematerialise, taking our new friends with us, then rematerialise in the inner asteroid belt, nice sunny spot, and dematerialise leaving them behind to feed!’

  Out in space, the barnacles clinging to the TARDIS had multiplied until it was buried beneath a sphere of thousands of bumpy shells. The creatures ejected clouds of spores which swiftly grew into minuscule barnacles, which attached themselves to the sphere and quickly expanded to become full-size barnacles.

  Then there was a wheezing, groaning sound, and the ball of blistering barnacles faded away.

  In the flight deck of the Godspeed, the emergency lights grew brighter. Then the main viewscreen lit up, showing the hull of the ship now clean of barnacles, followed by all the workstation viewscreens.

  The crew stared at each other in surprise. Keinholz checked his controls. ‘Emergency generators on line. Power supply at forty per cent and rising. We’re saved. We’re saved!’

  Thelesa, Ferrier and the rest of the flight crew cheered in relief. The ventilation hummed on and blasted the room with warm air. Then the overhead lights flickered into life and the deck was restored to its normal bright appearance.

  ‘What happened?’ said Thelesa.

  ‘The barnacles,’ said Ferrier. ‘They’ve… gone. Completely disappeared.’

  ‘Yes, they’re all feeding in the asteroid belt,’ said Locklear, standing in the doorway. She strode onto the deck as though it was just another day at work. ‘Thanks to the Doctor.’

  ‘The Doctor?’ said Ferrier. ‘But how?’

  Locklear sighed ruefully. ‘He took them out to lunch.’

  * * *

  ‘The Eye of Harmony. Exploding star in the act of becoming a black hole. Time Lord engineering. You rip the star from its orbit, suspend it in a permanent state of decay.’

  The Eleventh Doctor, Journey to the Centre of the TARDIS (2013)

  * * *

  On 28 November 1967, as the Second Doctor battled the Ice Warriors for the first time in Doctor Who, two Cambridge University radio astronomers – Jocelyn Bell Burnell from Northern Ireland and Antony Hewish from Cornwall – detected something strange in space. Every 1.33 seconds there was a pulse of energy – radio waves – from the same part of the sky. Or, rather, the place it was coming from slowly moved, but perfectly in time with the movement of the stars as the Earth rotated under them (as we saw in Chapter 1). That meant it was very unlikely that the pulse had been created on Earth: it had to be coming from somewhere deep in space.

  Bell Burnell and Hewish called the pulse LGM-1, short for ‘little green men’, because the regularity of the pulse at least suggested that it was artificial in origin, as if some kind of alien life form had engineered it. Scientists soon worked out that the pulse was a natural phenomenon, produced by a kind of star, but the explanation turned out to be just as remarkable as if it really had been some alien broadcast.

  Stars like the one Bell Burnell and Hewish found are now called pulsars – short for ‘pulsating radio star’ – because of the regular pulses of radio waves they create. The pulses are the result of two characteristics of a pulsar. First, they have strong magnetic fields. Earth also has its own, less strong magnetic fields which can interact with particles emitted from the Sun to create dazzling displays of light in the atmosphere, usually at high latitudes near the North and South Poles. These displays are called aurora, or the Northern and Southern Lights. Jupiter, Saturn, Uranus and Neptune also have magnetic fields that create aurorae.

  The Earth’s relatively weak magnetic field is able to funnel electrically charged particles from the Sun down over our planet’s poles, where they collide with molecules of air high above the ground and cause them to glow. But the magnetic field of a pulsar is around a trillion times stronger than the Earth’s, blasting charged particles away from its magnetic poles and out into space. As they accelerate, these particles emit radio waves along their direction of travel, creating a narrow beam of electromagnetic energy that shines out from each of the star’s two magnetic poles. But the magnetic poles are not precisely lined up with the star’s axis of spin (this is also true on Earth, which is why the magnetic north indicated by a compass needle
is a few degrees different from the true, geographical north shown on maps). As the pulsar spins, these beams of radiation sweep around the sky, and each time one passes over the Earth we detect a pulse of radio waves. Imagine a lighthouse with a revolving lantern at the top, casting out a beam of light. The beam sweeps round and round in the darkness but if you were out at sea, too far away to see the lighthouse, you’d see a regular flashing on and off of light. (With the pulsar, only one beam hits the Earth; the other is facing in the wrong direction.)

  Of course, the speed of the pulse that Bell Burnell and Hewish found showed that the pulsar had to be revolving very quickly – every 1.33 seconds. This is dizzyingly faster than the rotation period of an ordinary star like our Sun, which spins once every 24.47 days (measured at its equator). Even the Earth’s 24-hour rotation seems leisurely by comparison. But this incredible speed wasn’t the strangest thing about the discovery of the first pulsar.

  Astronomers knew that when a very large star reaches the end of its life, it explodes – in what’s called a supernova – leaving behind a huge cloud, or nebula, of gas called a supernova remnant. The gas ejected in these violent stellar death throes can eventually condense and collapse to form a new generation of stars and planets but some physicists wondered whether supernova explosions might also leave something else behind. They calculated that, as the outer layers of the dying star were blasted into space, the star’s core would suffer the opposite fate, being crushed and squeezed by gravity into a tiny remnant made almost entirely of neutrons. They called this theoretical remnant a neutron star. It would contain almost as much matter as our Sun, but squeezed into a compact ball just ten kilometres across. A teaspoon full of this incredibly dense material would weigh as much as a thousand Egyptian pyramids. That might come in useful: a spaceship made of such material would have so much mass it could warp space, allowing it to cross long distances more quickly. That’s what happens in the Doctor Who story Warriors’ Gate (1981), with the ship made of ‘dwarf star alloy’.

  The pulsar discovered in 1967 was spinning so rapidly that astronomers knew it must also be very small – just a few kilometres across. Yet its intense magnetic field implied that it contained a mass similar to that of the Sun. The pulsar was clearly a neutron star – the first one ever found.

  However, by the same calculations with which physicists had predicted the existence of neutron stars before finding one, some had suggested that the explosion of an even more enormous star would create a sort of funnel of increasing density which would have extraordinary properties. In 1964, an American science journalist, Ann E. Ewing, came up with a name for this amazing (and, some thought, ridiculous) idea: she called the funnel a black hole.

  * * *

  ‘A black hole’s a dead star. It collapses in on itself, in and in and in until the matter’s so dense and tight it starts to pull everything else in, too. Nothing in the universe can escape it. Light, gravity, time. Everything just gets pulled inside and crushed.’

  The Tenth Doctor, The Impossible Planet (2006)

  * * *

  The gravity of an object depends on how much matter it contains, and the more densely its matter is squeezed together the more intense its gravity becomes. This gravity warps the space-time around the object, causing nearby objects to fall towards it. We discussed in Chapter 1 how a very massive object such as our Sun warps its surrounding space-time so much that the planet Mercury doesn’t appear where it ought to according to Newton’s laws of gravity.

  A black hole contains at least four times as much material as our Sun, but squeezed into a region far smaller than a neutron star. As we see in the Doctor Who episodes The Impossible Planet and The Satan Pit (2006), it’s very difficult for anything – such as a planet or spaceship – to escape the enormous gravitational pull close to a black hole. But the closer you get, the stronger the gravitational pull becomes. At a certain distance – called the event horizon – the pull is so strong that you would need to be moving faster than the speed of light to escape it. According to Einstein, nothing can move faster than the speed of light, which means that nothing – not even light itself – can escape the gravitational pull at this point. (According to Doctor Who, the TARDIS can, which is why it can rescue spaceships from inside a black hole, as it does in The Satan Pit.) Once inside the spherical boundary of the event horizon your fate is sealed. All possible trajectories lead only to the centre of the black hole – a point of zero size and infinite density which physicists call a singularity.

  If light cannot escape from a black hole, we’ll never be able to see one directly – which is why they were given that name. But the discovery of a neutron star proved the theory that had predicted them, and suggested that black holes might really exist, too. That encouraged more physicists to puzzle out what they would be like and to look for them.

  How can you find something that’s effectively invisible – because light can’t escape from it? There are ways of detecting things that are otherwise invisible, by looking for the effects that they have on their surroundings. For example, in the Doctor Who story The Daleks’ Master Plan (1965–1966), the Doctor, Steven and Sara are transported to another planet, but don’t know where they are. We see they are not alone: an invisible something leaves a trail of footprints as it follows the Doctor. Later, when the invisible creature makes a noise and moves the branches of the foliage, the Doctor strikes out with his walking stick – and makes contact with something he cannot see. He strikes again, confirming his suspicion that it’s an invisible creature and forcing it to retreat. From this encounter, he deduces that he has just been attacked by a Visian, which means he’s on the planet Mira.

  In the same way, we can deduce the existence of invisible black holes from their effects on their surroundings. Rather than leaving footprints or moving foliage, material from nearby can spiral round the black hole in what’s called an accretion disk. The strong gravitational field close to a black hole can pull nearby gas towards it, making it spiral inwards faster and faster and heating it to extremely high temperatures. Before it disappears for ever inside the black hole’s event horizon, this doomed material emits a blaze of radiation, from infrared to X- and gamma rays, allowing our telescopes to detect it.

  At slightly larger distances from a black hole, objects can – just about – orbit safely, but the hole’s extreme gravity yanks them round at very high speeds. An object such as a star moving in such a tight orbit will still be visible and its rapid motion can betray the presence of an invisible companion – the black hole. Astronomers can detect this motion by studying the spectrum of light which the star gives off. In 1972, astronomers Louise Webster and Paul Murdin at the Royal Greenwich Observatory and Charles Thomas Bolton at the University of Toronto published evidence of exactly this phenomenon, suggesting they had found the first black hole: Cygnus X-1. The discovery – or all the talk about black holes generally – inspired the people making Doctor Who at the time.

  * * *

  ‘Singularity is a point in space-time which can exist only inside a black hole. We are in a black hole, in a world of antimatter very close to this point of singularity, where all the known physical laws cease to exist. Now, Omega has got control of singularity and has learned to use the vast forces locked up inside the black hole.’

  ‘Now, that is how Omega is able to create the world we are now living in – by a fantastic effort of his will.’

  The Second and Third Doctors, The Three Doctors (1972–1973)

  * * *

  The Three Doctors was the first Doctor Who story to feature a black hole, and its writers also threw in another exotic (but unrelated) prediction of theoretical physics called antimatter (see here). It’s a very important black hole, created by a Time Lord engineer called Omega as the power source that originally gave the Doctor’s people their mastery over time. In fact, just as we refer to ‘the’ Sun when it’s only one of millions of similar suns out in space, the Time Lords refer to this as ‘the’ black hol
e.

  In fact, we now know that at the centre of every galaxy is a ‘supermassive’ black hole – yes, that’s what astronomers really call them. The supermassive black hole at the heart of our galaxy, the Milky Way, is estimated to have a mass four million times that of our Sun (which is itself 330,000 times the mass of Earth). That’s the material of four million stars squeezed into a tiny point at the centre of the galaxy. Don’t worry, though: we’re at a very comfortable distance of 26,000 light years from this monster black hole: in fact our solar system, and almost everything else in the galaxy, is safely orbiting round it.

  How do we know this if, again, we can’t see a black hole? The deduction work goes like this. It takes our solar system over 200 million years to make one complete orbit around the galaxy, but stars in the centre of the Milky Way zip around their orbits in just a few years. Moving at such rapid speeds, these stars would be flung out of the galactic centre unless there was a very powerful source of gravity – and yet no object is visible to hold them in place. From their speeds and the size of their orbits scientists can calculate the mass of the central, invisible object. It turns out to be very small but very massive indeed – and invisible. A supermassive black hole is the only answer that makes sense.

  But how could a black hole help Doctor Who’s Time Lords travel in time? We already know that an object with a large mass warps space-time. If you were standing on the surface of a neutron star – wearing a special spacesuit so you were not squished by the intense gravity – time would be slowed down by about thirty per cent compared to time on Earth. Time would seem to pass normally for you, but if somehow you could see the Earth from where you stood, things happening there would appear to be speeded up. Effectively, the neutron star’s gravity would allow you to travel through time by fast-forwarding into the Earth’s future.