These are the little problems that you hit when you’re trying to write sci-fi. It’s quite often not about the epic narrative arc or the coherent vision for the future; it’s all about the mundane stuff. What do people drink when they need to wake up of a morning? Are colds now extinct? Do people still celebrate Christmas? What’s an appropriate term of endearment?
One of the ones that I battled with for a while was the ‘Metric vs Imperial’ debate. I was half tempted to give up on it totally and make up my own units but that quickly retreated from that complicated little idea. The whole point of words – especially words in fiction – is that they spark off the appropriate images and connotations in a reader’s mind (and I’d given myself enough of a headache by creating a brand new military ranking system). The more shorthand you can use, I think, to achieve this the better, hence the ubiquitous rule about chopping out any adjectives and adverbs.
In the brilliant TV Tropes site they suggest it’s most common to use metric system for science fiction and imperial units for fantasy. There’s no real rational reason for this, of course, beyond a ‘feeling’ that metric sounds more futuristic.
I thought I’d check what other classic science fiction authors have done in the past, so picked a few books at random off my book case. Arthur C Clarke goes with ‘kilometres’ and ‘metres’, Iain M Banks has ‘kilometres’. But Larry Niven had ‘miles’, which surprised me. Neal Stephenson (for Anathem) has gone for ‘miles’ and – I love this one – ‘paces’ for his ‘metres’ equivalent. But then Anathem is the kind of book that needs this, I think.
There may be a UK vs US writers divide here … or it might be a ridiculously small sample size. I’ll let you decide.
Anyway, in the end, I went with metric. It still feels correct, more futuristic. What I couldn’t find myself doing was denoting smaller sizes in centimetres, though. I’m not sure why … but just it just felt wrong, to describe something as ‘thirty centimetres high’. That was when I itched to be able to write ‘about a foot’ again!