How would you power the Doctor’s TARDIS?

By Dr. Robin George Andrews 

Series 9 of Doctor Who premieres on the 19th September with The Magician’s Apprentice. In the meantime, another (lesser known) doctor, Dr. Andrews, has been pondering on the power source of the TARDIS: the Eye of Harmony.

That’s right: the man who stops the monsters is back, and he’s not alone. The Master – reincarnated as the phenomenally mischievous Missy – is somehow alive and kicking, and is teaming up with the intrepid, effervescent Clara to try and find the Doctor. Dalek hordes from Skaro, a mysterious recurring pair of sunglasses, the Doctor rocking out on an electric guitar, and an extraordinary universe full of people needing to be saved all feature within just the first few episodes of the new series. Very little about the series is known, but this particular Whovian has been wondering about the Gallifreyan’s motor itself for awhile; specifically, how on Earth does he power his blue box, travelling so gloriously and recklessly through all of time and space?

Within the cloister room of the considerably roomy TARDIS resides the Eye of Harmony, something that the good Doctor describes as “an exploding star in the act of becoming a black hole, suspended in a permanent sense of decay”. This mysterious artificial black hole – or rather, a star frozen at the moment of its cataclysmic implosion – powers the famous time machine, somehow harnessing this energy.

There’s no doubt that the energy involved in producing a back hole of even a “small” size would be extraordinary. So would it be possible to power the TARDIS through the generation of an artificial black hole, assuming it could be carefully caged and harnesses?

A black hole, putting it simply, is an object of infinite density that has effectively ripped a hole in the fabric of the universe. They exist when supermassive stars reach the end of their lifespan – itself a fascinatingly destructive process – and collapse on themselves as their gravitational pressure defeats the outward radiation produced by the burning of stellar fuel. Chillingly, nothing can escape from a black hole. Particles of matter or any form of electromagnetic radiation, including light, can escape once the event horizon – the point of no return – has been crossed.

Their existence is detected not through direct observance – as light is sucked into an eternity of oblivion, we cannot “see” the black hole with our own eyes or scientific instruments detecting such radiation – but rather by their interaction with space-time around it. The light from stars directly behind a black hole can often be seen; the distant light cascades towards the black hole and, as the fabric of the universe itself has been warped and curved by this infinitely dense point, bends around it. Sometimes, as the black hole gobbles up a nearby star, it spins and rotates around the singularity at incredible velocities before eventually falling past the event horizon in a freakish light show known as an accretion disk.

What happens to an object as it falls into a black hole, including that of the original star itself, is a hotly debated topic in physics. All physical matter has “information”: quantifiable data, like its mass, its various energy states, its momentum and so on. Whatever happens to this matter as it speeds through the universe, it will always have information that we, as observing humans, can detect. Unfortunately, when matter tumbles into a black hole, we can no longer observe it, as nothing detectable escapes the maw of these galactic titans.


Even black holes aren’t ageless, immortal beasts: as Stephen Hawking first predicted in 1974 that black holes should also emit radiation, somewhat counter-intuitively when their intense gravitational pull is taken into account. Fluctuations in the energy state of the super vacuum of a black hole causes pairs of particles and their precise opposites, antiparticles, to appear near the event horizon. Normally, if a particle impacts its counterpart antiparticle, they will obliterate each other; however, the gravitational whirlpool of the black hole snatches one of these particles back into oblivion, whilst the other one escapes into space.

This particle shooting off into the dark regions of deep space could then be detected by an instrument. This lucky particle has something called “positive energy” – the standard energy that objects in the universe have, whether that be kinetic, or potential, or sound or thermal, and so on. The unfortunate particle chewed up by the black hole, strangely, has something called “negative energy”. Negative energy exists to balance out the positive energy. For example, if you drop your iPhone to the floor – you clumsy fool – it will gain kinetic energy as it falls, which is positive energy. However, the gravitational pull of the Earth will match that of the kinetic energy as it falls to the floor and cracks. This negative energy required to bring two objects – in this case, your poor iPhone and the planet – together is balanced precisely by the positive energy is gained as it fell down to the Earth.

The positive energy of the escaped particle is emitted into the wider universe. Conversely, the particle that is munched up by the greedy black hole has negative energy. As the black hole continuously produces these particle-antiparticle pairs, and continuously absorbs the ones with negative energy, it begins to lose energy itself. As Einstein showed with his famous equation E = mc2, mass and energy are equivalent to each other. So if the black hole is continuously losing energy, it is also continuously losing mass.

Through this process, known as Hawking Radiation, a black hole will eventually evaporate and die away.

I know: this is a lot to get your head around. I’m not a physicist – I’m a volcanologist – but hey, remember, the Doctor’s TARDIS is at stake here.


The black hole at the centre of the TARDIS is apparently kept in a state of suspended animation, just at the point of its formation. I’m going to say that the Doctor’s lying here – something he makes a habit of, come to think of it – and that the Eye of Harmony is undergoing continuous Hawking Radiation. If so, then perhaps that’s what powers the TARDIS: the continual emission of Hawking Radiation, and the harnessing of all this positive energy.

In 1983, the physicists George Unruh and Robert Wald explored exactly this mechanism for harnessing the power of a black hole. For a back hole formed with the mass of our own Sun, however, the positive energy of the particles produce by Hawking Radiation is entirely negligible and completely useless.

What about the negative energy particles that get sucked back across the event horizon? What if they were snatched up by the TARDIS before they crossed the line? If these doomed particles are rescued whilst they are accelerating at incredible speeds towards the black hole, a vast amount of negative energy could theoretically be captured, according to Unruh and Wald. This capturing of the negative energy – the acceleration radiation, if you will – would yield remarkable power. They estimated that more energy could be “mined” every second from a small black hole than that which is radiated per second from every single star in the observable universe.

Not only that, but the black hole itself would not evaporate or die, as it isn’t receiving any of these negative energy particles. Remarkably, for once, I guess the Doctor wasn’t lying: the Eye of Harmony could last forever in this state.

I don’t know about you, but if you need to power a time machine, this sounds like a good way to get the energy to do it. Although perhaps I should just ask Brian Cox about this: after all, he’s popped in to the TARDIS once or twice himself, the jammy dodger.

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