She brought me to a new chamber, deep within the Spline ship. Criss-crossed by struts of cartilage, this place was dominated by a pillar made of translucent red-purple rope. There was a crackling stench of ozone.

I knew where I was. ‘This is the hyperdrive chamber.’

‘Yes.’ She reached up and stroked fibres. ‘Magnificent, isn’t it? I remember when I first saw a Spline hyperdrive muscle—’

‘Of course you remember.’

‘What?’

‘Because it’s now. This is my first time seeing this. And I’m you.’ Some day, I thought gloomily, I would inevitably find myself standing on the other side of this room, looking back at my own face. ‘Don’t you remember this? Being me, twenty years old, meeting - you?’

Her answer confused me. ‘It doesn’t work like that.’ She glared at me. ‘You do understand how come I’m stuck back in the past, staring at your zit-ridden face?’

‘No,’ I admitted reluctantly.

‘It was a Tolman manoeuvre.’ She searched my face. ‘Every faster-than-light starship is a time machine. Come on, ensign. That’s just special relativity! Even “Tolman” is the name of some long-dead pre-Extirpation scientist. They teach this stuff to four-year-olds.’

I shrugged. ‘You forget all that unless you want to become a navigator.’

‘With an attitude like that you have an ambition to be a captain?’

‘I don’t,’ I said slowly, ‘have an ambition to be a captain.’

That gave her pause. But she said, ‘The bottom line is that if you fight a war with FTL starships, time slips are always possible, and you have to anticipate them . . . Think of it this way. There is no universal now. Say it’s midnight here. We’re a light-minute from the Base. So what time is it in your fleapit barracks on 529? What if you could focus a telescope on a clock on the ground?’

I thought about it. It would take a minute for an image of the clock on the Base to reach me at lightspeed. So that would show a minute before midnight . . . ‘OK, but if you adjust for the time lag needed for signals to travel at lightspeed, you can construct a standard now - can’t you?’

‘If everybody was stationary, maybe. But suppose this creaky old Spline was moving at half lightspeed. Even you must have heard of time dilation. Our clocks would be slowed as seen from the base, and theirs would be slowed as seen from here. Think it through further. There could be a whole flotilla of ships out here, moving at different velocities, their timescales all different. They could never agree.