The Arrows of Time

‘Why should we subject our descendants to that kind of torture? We can turn the Peerless around right now, confident that it will support us long enough to complete the trip.’

Lila brought an image onto her chest; the room’s camera picked it up and displayed it on the giant screen behind her. ‘This is the plan,’ she said. ‘This was always the plan, from the day Eusebio broached it with Yalda.’ The sight was enough for Agata to feel a latent impression of the same familiar curve, ready to rise up on her own skin. This was the map of her life’s purpose; she’d understood that since the day she’d first seen it.

‘We know we can make the turn,’ Lila said. ‘All the way around that semicircle, the acceleration we need can be produced with the engines sending photons into the future of either the home cluster or the orthogonal cluster. Only the last stage of the journey presents a problem: it’s not clear how we can begin to decelerate in the approach to the home world. But we’ll have six more generations to address that, and I can’t believe it will prove insurmountable.’

Lila glanced at the timer. ‘To describe this plan as “dangerous” is absurd. Dangerous compared to trying to give birth to children made of negative luxagens? I don’t think so!’

The timer rang. Most of the crowd cheered; Agata ignored her mother’s look of lofty amusement and joined in. Lila deserved the encouragement. Pio’s ideas weren’t likely to get much traction, but with the vote less than a stint away they needed to be refuted decisively for the sake of everyone’s morale.

Pio dragged himself forward again. ‘What dangers would the return pose?’ he asked. ‘Let’s start with a wildly optimistic view, and suppose that the entire journey could be completed safely. Once we reach the home world and deal with the Hurtlers, the barbarians are sure to be grateful – for a while. But could we really live among them, after so much time apart? I can’t see them approving of our ideas about governance, let alone our reproductive methods, and my guess is that they’d hold Starvers in almost as much contempt as Shedders. Then again… since we’ve made such a habit of bequeathing tasks to our descendants, maybe the last one could be to devise the kind of weapons they’d need to defend their way of life against the planetary status quo.’

Agata shifted uncomfortably on her rope. She knew he was being sarcastic, but any talk of weapons put her on edge.

Pio said, ‘That’s the optimistic view, but the real problems will arise much sooner. As we decelerate for the turn, we’ll be moving at ever greater speeds with respect to the Hurtlers. For a long time our spin has been enough to fling these specks of dust away, and now we have a fancy system of sensors and coherers guarding the slopes so we can spin-down the mountain with impunity – but even the coherers won’t be able to protect us once the Hurtlers are moving faster than the fastest radiation we can actually detect.’

The audience fidgeted, underwhelmed. Everyone knew that the Peerless was a small target, and though it was true that the mountain’s defences would be useless once the Hurtlers crossed a certain threshold velocity, the period of vulnerability would be brief.

Pio inclined his head slightly, acknowledging the weakness of the point and moving on. ‘Lila assures us that the engines won’t need to violate any thermodynamic laws as we turn the Peerless around. But how certain can we be that they really will keep functioning? And even if the turnaround itself proves uneventful, keep in mind that the entire return journey entails our own arrow of time pointing against the arrow of the orthogonal cluster – a configuration we’ve never experienced before.’

Agata couldn’t contain an exasperated hum. The most dramatic effect she expected from the reversal was for the orthogonal stars to vanish from the sky.

‘Beyond those disturbing uncertainties, no one has the slightest idea how we could commence the final deceleration. Lila herself admits as much!’ Pio paused to let the audience dwell on this – despite his own cheerful confession that he had no idea how a viable migration scheme would work. ‘Imagine what it would mean to be trapped in this mountain, heading back into a region full of ordinary matter but unable to slow down and match speeds with it. Every grain of interstellar dust we encountered would strike us with infinite velocity – rendering it as lethal to us as a Hurtler would be to the ancestors. Astronomers in Yalda’s day searched the sky for years to find the safe corridor we’re moving through now. We should take their gift and make the most of it: we should remain on this trajectory for as long as it’s clear, and use the time to prepare ourselves to step away from all of these colliding worlds and find a home that will be safe for eons to come.’

As Pio reached down to reset the timer there were a few scattered cheers.