Think through the implications of your handwaves

SPOILERS for tonight’s episode of Doctor Who.

Very much enjoyed tonight’s episode. It’s nice to see the series having the confidence to use time travel as a story device, rather than just as a setup for adventures-of-the week in different settings. There were some great dramatic moments, especially towards the end, and it did a decent job of exploring the ethical implications of time travel rather than sidestepping them, leading to some dramatic moments. It was also very nicely paced: I loved the speed with which it got through the initial setup, and the abruptness with which it cut to the end credits.

I think the only major thing I’d have changed would have been the reason why the accelerated time stream that Amy gets trapped in exists. I’d also have added food dispensers around the place, rather than a ‘you don’t need to eat in here’ handwave. These details set my science-fiction-writer mind off thinking about their implications, which distracted me frm the point of the episode.

All the episode needed was a time-acceleration field where years passed inside for hours outside, but what it gave us is a field that selectively accelerates some biological processes and not others. Someone in the field experiences life, and ages, at the ‘fast’ rate; but diseases and the need to eat only progress at the ‘slow’ rate. A whole lot of energy is being magicked into Amy’s metabolism in order for her to keep functioning for 30-odd years without eating. The more you think about this, the less it makes sense. Suppose Amy cries or sweats: does she need to drink to recover that fluid? If her hair and nails keep growing and her skin cells replenish, where does that new mass come from if she doesn’t eat? (If her hair and nails aren’t growing, and her skin isn’t replanishing, how is she showing physical signs of aging?)

My first thought was: these aliens could create an accelerated time-field within which you can live life normally except that you don’t suffer from diseases and you don’t need to eat. Judging from the size of the facility, they had no problem creating this field over a large area. Why reserve it for people who had the plague? Why didn’t they all live inside it permanently?

The plague itself they could get away with by saying it’s a magic time-plague that somehow knows what time it is outside (which ties in nicely with a Time Lord being affected by it but not a human), but there was no need for the metabolic implications of Amy not needing to eat. I think it’s an example of two mistakes that can be made when writing science fiction:

Firstly, not thinking through implications. The writer comes up with a one-line handwave of something inconvenient (in this case, Amy not eating for a week) and doesn’t think through what this means. A different hand-wave (e.g. there’s a food dispenser in the room) could have worked just as well without the implications.

Secondly, fuzzy thinking about time passing at different rates. To use a different example, at first glance it makes sense that our hero might know he’s in a time-freeze because his watch has stopped–but if he’s able to act normally then the mechanical processes of his body must still be working, so how does the watch know to behave differently? Similarly, if Amy’s muscles can move at the normal rate for her new time stream, how does her digestive system know to slow down? If time is passing at a different rate, that should affect everything, and you should only see effects at the boundary between one time rate and another (e.g. you can look out of your slow-time bubble and see clock hands whizzing round, but your wristwatch should be working normally from your point of view). If you want a more complicated effect, you’ve got to have a different cause.

(For example: the two-streams facility could put the plague victim into a life support unit and plug their brain into a computer. With the aid of the computer, their consciousness lives at a greatly accelerated rate, inside a virtual-reality environment. The plague is still working on their real body out in meatspace, in real time, and the VR environment doesn’t have to make them feel hungry if they don’t want to eat inside the simulation. The simulation could age their simulated body at the normal rate, although there’s no technical reason why it has to. Family and friends could exchange messages via the computer, or even visit by temporarily jacking themselves in. Although, again, I’m wondering why this should be reserved for plague-victims…)

Yes, that’s a lot of text devoted to a nit-pick of what was generally an excellent episode, but in science fiction a lot can hang on technical details and it’s important for writers to think them through.

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