The most scientifically illiterate episode ever? Doctor Who – Kill the Moon

In the first series of the fourth Doctor, Tom Baker, a robot grows to enormous size — and, apparently — mass after having a high powered laser directed at it. Scientifically implausible, or, at least, apparently a significant error of units. In Planet of the Daleks, a Jon Pertwee adventure, invisibility becomes available through no adequately explained mechanism. We’re well used to being bamboozled by reversal in the polarity of the neutron flow, multi-dimensionality which sometimes stops weapons working in the TARDIS and sometimes doesn’t, and deliberate plot holes left to tease us, such as in the recent Robot of Sherwood adventure.

However, last night’s ‘Kill the Moon’ was probably the most scientifically illiterate story ever written for the Time Lord. This is not to say it was a bad episode — we probably reached a peak of emotional literacy, as Jenna Coleman and Peter Capaldi play exquisitely off each other, with more help from the cast of Spooks, this time with Hermione Norris doing the honours to follow Keeley Hawes in Time Heist.

This is the premise: the moon has suddenly started becoming much more massive, causing unsurvivably high tides right across Earth. A museum relic space shuttle and three antiquated astronauts are despatched with nuclear bombs to sort it out. The Doctor arrives in the usual nick of bad timing, and is immediately taken with the unseasonally high gravity. When asked what could have caused it, he speculates on a number of plausible-sounding technologies. Fair enough: Doctor Who science often operates on a ‘don’t ask, don’t tell’ basis.

However, when the truth becomes known, it turns out that an enormous space-bat-angel-dragon (to borrow a phrase from Ted Hughes) is getting ready to hatch because the moon is not a planetoid, but a stupendous egg.

A planet which is a living being may remind you of Blake’s 7 Series 2 episode 6 Trial, or of numerous other science fiction adventures. It’s a grand idea, but not implausible that it’s happening somewhere out there. As Clara points out, it is a little implausible that the Doctor never heard of it before, but, there you go, that’s time travel.

What is not merely implausible, nor even merely impossible, but simply scientifically illiterate is the notion that a creature growing inside an egg will change its mass as it grows. It won’t — a hermetically sealed egg, provided that you don’t paste something onto it, or break the shell, will stay pretty much the same mass for pretty much ever.

Of course, there are lots of ways that a space-creature, unique in the history of the universe, might gain mass. It could come through a time vortex from some other time — actually, the problem of matter being destroyed in one time and recreated in another is never adequately addressed in Doctor Who. It could come by some kind of cosmic wormhole from a black hole elsewhere (actually, it couldn’t, but, by SF convention, you could get away with it). It could even come by gradual accretion of meteors hitting the moon and being absorbed, or a whole load of asteroids crashing into it in one go.

However, in the episode, this is not what happens. Someone clearly never explained to the script writer that while things may change their size, they never change their mass, except as a result of bits being added from elsewhere, or removed, or the conversion of massive amounts of energy for comparatively paltry amounts of matter.

To make matters worse, at the end, the creature, without having actually eaten anything, lays a new moon, of evidently equal mass, since it returns earth tides to normal.

What? Just what? what? what? what? what?


I recently read a review on Amazon of a low wattage kettle, which I wondered might be suitable for heating water in a Land Rover. The reviewer pointed out that it took much longer to boil the kettle (rather like the hotel room in which I’m typing this, where the kettle takes 3 minutes to boil enough water for one cup of tea), but that he was glad to do so because it saved energy and therefore was counteracting climate change.

Well, no. To boil the same amount of water from the same starting temperature requires the same amount of energy. If you have a lower power, it takes longer. 1 amp of current at 230 V will take 13 minutes to boil the same amount of water as a 13 amp kettle would boil in 1 minute, provided that the two kettles were equally efficient. Kettles are actually pretty efficient devices, and are preferable to microwaves or hobs if you just want to boil water.


How much energy is required to push a ball up a slope to a height of 30 centimetres? Is more energy required if the slope is steeper? Is less required if the slope is gentler? Actually, the opposite, because in the steep case you require only the energy to raise it plus the energy to move it along the flat length of the slope. In the gentle case, this is also true, but the flat length is longer, and so more energy is required.


I think the chap who reviewed the kettle and the people who think that a gentle slope requires less energy than the steep slope should be forgiven: the one was a user-contributed review on Amazon, while the other is plausible (though incorrect), if we think of how exhausting it is for a human to do the task, or the requirements of a powerful four-wheel drive vehicle if the slope is very steep. What’s actually happening in both those cases is that all kinds of inefficient processes are taking place to change the result.

The fact-checkers — if they still exist — for Doctor Who, though, really should know better. If you’re going to transgress the basic principles of physics, you at least need to have a plausible explanation.

Probably won’t be watching that one again…

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