The Arrows of Time

by Greg Egan

  Agata buzzed wearily; at least she wouldn’t be debating Pio. ‘Have your own family taken positions?’

  ‘Gineto against, Serena for, Vala undecided.’ Medoro didn’t seem too worried by the split. ‘But they all gave me grief that I didn’t go public.’

  ‘That’s unfair,’ Agata protested. ‘Ramiro had it all laid out for him. We were just guessing – it would have been irresponsible to start a rumour when we weren’t even sure of the facts.’

  ‘Hmm.’ Medoro sounded unconvinced, so Agata let the subject drop.

  She said, ‘But now Ramiro is courage personified, and I have to stand in front of a crowd of his admirers and tell them he’s wrong.’

  ‘I’m sure you’ll have admirers too,’ Medoro teased her.

  ‘For what? My theorems on sectional curvature?’

  ‘Why not? Any idiot can set himself on fire.’ Medoro rearranged himself on the guide rope. ‘Anyway, you don’t need to attack Ramiro. His arguments aren’t unreasonable: of course there could be drawbacks if the system is abused. But that doesn’t mean we can’t minimise the risks.’

  ‘I was going to start with a few practical benefits,’ Agata said. ‘Suppose we learn that a new crop disease shows up three years from now. We can’t prevent it arising altogether – or we’d never hear about it – but we can still take early quarantine measures and ensure that the outbreak is limited.’

  ‘Boring but sensible,’ Medoro declared approvingly. ‘Exactly the kind of thing people want the Council to be doing. Throw in a reference to the Great Holin Shortage, and you’ll have won over half the women in the room. What about averted collisions?’

  Agata said, ‘No – in most realistic cases we would have had plenty of warning by conventional means.’

  Medoro was disappointed. ‘You don’t want to go for the frisson of danger? Message: “Thanks for starting a sideways swerve when you read this, it just paid off and saved the whole mountain”?’

  ‘I could raise it briefly,’ Agata decided. ‘Almost as a joke, so Ramiro can’t go too hard on the implausibility.’

  ‘What else?’ Medoro pressed her.

  ‘Next, reassurances about privacy, validation and containment. Everything can be encrypted and signed, in exactly the same way as with the ordinary network. So there’ll be no chance of anyone else reading a message intended for you personally, and no chance of the sender convincing you that they’re someone they’re not.’

  Medoro said, ‘I can check a message that purports to be from you because you’ve published a validation key – and you’re here to complain loudly if someone else tries to distribute a different key and claim that it’s yours. But if I get a message from someone who claims to be my grand-niece . . . how do I authenticate that?’

  ‘You just need a chain of trust,’ Agata explained. ‘You get a message from your niece, signed with a key that you’ll give her personally when she’s old enough. Her message gives you a key for authenticating her daughter’s message.’

  Medoro grimaced. ‘So I need to have one key ready right now, and be sure that it won’t get lost or stolen before I have a chance to give it to a child who hasn’t been born yet?’

  ‘Yes. But is that so much harder than keeping your own key secure?’

  ‘I think I deleted my key,’ Medoro confessed. ‘That’s why I never sign messages any more; I’m too embarrassed to apply for a replacement.’

  Agata said, ‘If Ramiro raises that kind of problem, what can I say? Nothing’s perfect, we can’t expect it to be, but we cope with the flaws in every other technology.’

  ‘You mentioned containment,’ Medoro reminded her. ‘Suppose your neighbour hears from her son about your death; how can you stop her telling you the details, if you don’t want to be told?’

  ‘Punishment,’ Agata said. ‘If you violate someone’s right to be future-blind, all messages addressed to you will be deleted henceforth.’

  ‘Not that anyone would bother sending them any more,’ Medoro reasoned. ‘But can’t we strengthen that further, and make it impossible to do the damage in the first place?’

  Agata was amused. ‘I doubt it. I mean, the Council could declare that if someone receives a message that leads to an offence, the sender will never be allowed to send it in the first place. And if their ability to follow through on that were infallible, then it would never even need to be acted on. But realistically . . . ?’

  Medoro said, ‘I might have been overreaching there. What’s next?’

  ‘I won’t have time for much more, but I should end with something about the reunion.’ Agata waited for Medoro to mock her, but he listened in silence. ‘We all have stories of the launch, passed down from generation to generation. Why shouldn’t it be the same with the reunion? Why shouldn’t we all have that sense of completion?’

  ‘That’s reasonable,’ he said. ‘Don’t overdo it, though; just say enough for the people who’d be swayed by it to complete the picture for themselves – without starting the cynics groaning about ancestor worship.’

  ‘No talk of receiving photographs of our descendants strolling through Zeugma beside Eusebio?’

  ‘I think not.’

  ‘That’s all I have,’ Agata said. ‘Practical benefits, rigorous safeguards, future-nostalgic finish. The rest of the time I’ll need to be dealing with Ramiro’s arguments. So if you can think of any downsides I haven’t addressed, this would be a good time to hear them.’

  Medoro took a few moments to consider the request. ‘What about the idea that the system could be demoralising for innovators? You’ve been struggling for years to understand why the entropy gradients exist; how would you feel if you read a message from the future that handed you all of the answers, robbing you of the chance to discover them for yourself?’

  Lila had expressed similar misgivings, but when Agata had thought the matter through she had not been swayed. ‘Complex ideas don’t come out of nowhere,’ she said. ‘Not because that would violate some law of physics or logic, but because it’s stupendously improbable. The most probable routes to complexity involve some kind of backstory. There were no people around at the entropy minimum – it took eons for the first simple organisms to arise, and eons more for life to evolve to include a species with a complex culture.’

  Medoro was confused. ‘What has that got to do with some future rival stealing your glory?’

  ‘Complexity grows in a sequence of steps,’ Agata stressed. ‘So far, we’ve never seen it appear fully formed, and we have no reason to think that the messaging system could change that. If some future researcher did send me a theorem that made all my own efforts obsolete, it would enter the scientific culture and be passed down the generations – so whoever wrote the message would merely have heard the result during their own education: they wouldn’t be its discoverer.’

  ‘In which case . . . who would?’ Medoro struggled.

  Agata buzzed. ‘Nobody! And there’d be no contradiction in that, but it’s as unlikely for the cosmos to contain such an isolated loop of unexplained complexity as it would be for the same idea to have popped into my mind all by itself this morning, with no prompting from any future informant.’

  Medoro thought it over. ‘Suppose I take your word for all that. You’ve still only told me what you think won’t happen – you’ve given me an unlikely scenario. So what’s the alternative? What’s the likely story?’

  Agata said, ‘There’ll have to be some self-censorship of the messages. People won’t pass back ideas that would entail the creation of complexity out of nothing.’

  Medoro hummed with frustration. ‘Now you’ve introduced some magic cosmic censor?’

  ‘It’s not magic,’ Agata insisted. ‘It’s not some extra premise or some new constraint. If the messaging system can be built at all and the cosmos is self-consistent, the less improbable scenario – by far – is the one that contains some limits on the content of the messages, not the one that allows whole new sciences to come into existence wi
thout a day’s toil by anyone.’

  Medoro plucked at the rope, dissatisfied. ‘What if someone in the future decides to break this rule?’

  ‘They can’t, they don’t,’ Agata said flatly. ‘Or to be precise: it’s prodigiously unlikely. The fact that ordinarily such an act would be unexceptional is beside the point: the messaging system will put them in a situation where the prerequisite for such a disclosure is that they have something massively improbable to disclose in the first place.’

  Medoro wasn’t placated. ‘What happened to the freedom the engine tests gave us?’ he demanded.

  Agata said, ‘That’s just the freedom to send messages in general, not some open-ended guarantee that the usual range of actions will always be possible. You didn’t complain about our lack of freedom to ignore an outbreak of crop disease, if we get a message spelling out everything we will have done to contain it.’

  ‘No,’ Medoro admitted. He buzzed wryly, finally reconciling himself to the strangeness of it. ‘Maybe you should stay clear of this in the debate. It might make people feel a bit . . . trammelled.’

  ‘If Ramiro doesn’t raise it, I’ll have no reason to bring it up.’ Agata felt much happier about the whole subject after arguing it out with Medoro, but she wasn’t going to spread anxiety needlessly just to prove to people that she had the cure. ‘It’s going to be hard enough as it is.’

  ‘You’ll be fine,’ Medoro assured her.

  ‘Will I?’ Agata pictured herself at the front of the packed meeting room, ready to follow in Lila’s footsteps. Or possibly her brother’s.

  ‘I’d offer you an eyewitness report of your success,’ Medoro said. ‘But we can’t quite pull that off yet.’

  9

  Tarquinia reached across and squeezed Ramiro’s shoulder. Her hand made contact roughly, imperfectly controlled in the near-weightlessness, but that only gave the gesture more force.

  ‘Good luck,’ she whispered. Ramiro kept his rear gaze on her as he dragged himself away along the guide rope towards the stage.

  The meeting room was full, and brightly lit by the beams from a dozen coherers bounced diffusely off the ceiling. People were still talking among themselves as Ramiro approached the front of the stage and reached over to start the timer. He waited a pause or two for the echoing ping to grab their attention, but he knew it would only waste time if he held out for complete silence.

  ‘My job,’ he began, ‘is to automate things. There are many tasks where we already know exactly what we want to achieve, but find it too arduous to supervise the execution of our plans in detail. If I do my job well, though, the results are easy to foresee: you tell me what you want some machine to do for the next five stints, and I make that happen.

  ‘So I’m familiar with the advantages of control and predictability, and I can understand why the Council aspires to bring those qualities to as many aspects of the running of the Peerless as possible. If we could receive a message from the future assuring us that the mountain had reached the home world safely, and this message was accompanied by a list of the actions we’d need to take – or in the sender’s view, had already taken – to sidestep a host of potential calamities, then I’d have no complaint about that at all.’

  Ramiro let himself scan a few faces in the audience; so far, he didn’t seem to have offended anyone.

  ‘The problem,’ he continued, ‘is that if we build the proposed system, I don’t believe it would be possible to limit it to a single, clear-cut purpose like that. Whatever the Council decrees for now, they can’t control the way the facility would be used in the future. In practice, what will confront us is the photonic equivalent of a vast storehouse of documents whose content will have been determined by other people, some of them very remote from us in time. Over the generations, certain documents will have been removed – another process that will be out of our hands – while others are kept and passed down to us. If we hope to reap any benefit from whatever remains, we’ll have no choice but to appoint people to read and assess everything we receive. But people can’t forget things on command, and even people sworn to secrecy can’t ignore what they know. With all those messages and all those readers, information will spill out and reach the public, whether they want it or not.

  ‘Stories of distant calamities averted might bring us courage and optimism, but how would we respond to details of our own personal fates? Some bad news might well come through to us that serves no useful purpose at all: who would want to hear of an early death that no warning could prevent? And some good news would surely lose its lustre if revealed at the wrong time: look back on all the joyful surprises in your own lives, and ask yourselves if you really would have wished to be confronted with a list of them, years in advance. And even if you succeeded in remaining ignorant, how would you feel if your friends and rivals knew your future history? People might be compelled to seek as much news about themselves as possible – in spite of their original wishes – simply to prevent others—’

  The timer rang. Ramiro was startled; his pacing must have been slower than when he’d rehearsed with Tarquinia the night before. He flipped the lever and dragged himself back towards the rear of the stage. He’d barely registered Agata’s presence before, but now he forced himself to stop fretting about his poor timing and focus all his attention on her.

  ‘Ramiro has done me the favour of acknowledging the enormous benefits of this scheme,’ Agata began. ‘But he’s been rather vague about the details, so let me try to make the possibilities more concrete. Imagine receiving a message from the future telling us that one of the medicinal gardens had become infested with a species of goldenrod blight that we’d never encountered before. Unwelcome news, of course, and we’d be powerless to prevent it – but now imagine that message going on to explain that, thanks to this early warning, we would isolate all the other gardens in time to keep them safe.

  ‘I’m not saying that this system would be a panacea, but we could all make a list of dozens of tragic events where a warning would make all the difference. Imagine encountering some uncharted rock from the home cluster, crossing our path at infinite speed and wiping out a fire-watch platform – but missing the Peerless itself, thanks to a course correction that only a message from the future could have guided. Indeed, we could surround the mountain with expendable objects, purely for the sake of rendering near misses visible – just as that one blighted garden allowed us to save the rest.’

  Ramiro thought it more likely that consistency would be achieved by the rock simply destroying the Peerless, leaving no one to report on the event. But since he doubted that either kind of collision would actually occur, if he quibbled about it he’d just sound desperate.

  Agata had moved on. ‘All this talk about information bursting from the system and spilling down the corridors is fanciful. Has Ramiro never heard of encryption? If it’s good enough to protect our privacy now, why should we expect it suddenly to fail us? If there are messages from our future selves, we’ll be free to use all the protocols we use now when exchanging confidences with friends to ensure that no one but our present selves can read them – and of course, we’ll also be free to delete these messages unread if we choose to, strange as that would be. With the same methods, we can guarantee the privacy and authenticity of messages from our descendants, or indeed from anyone in the future who chooses to address us. So there’ll be no swarm of prying clerks sifting through our private mail, gossiping about us to their friends. Matters of public interest will be sent in plain text, but everything else will be person-to-person.

  ‘For those rare cases where some future informant and present-day recipient might act together out of spite to violate your wish not to be informed of certain events, we can discourage that with appropriate punishments. Nobody is claiming that this technology will transform us into a flawless society, but people have survived over the ages without any perfect, pre-emptive cure for hurtful gossip or malicious slander. Words can damage people, I acknowledge that, but i
t’s nothing new. We’ll find the right balance in our laws to protect against the worst kinds of harm, just as we’ve done in the past.’

  Agata had been stealing glances at the timer with her rear gaze and adjusting her pace. Now she waited a moment for it to start ringing, then reached down to silence it.

  Ramiro took her place. ‘Agata has expressed a touching faith in the power of the law and technology to protect us from unwanted personal revelations,’ he said. ‘I don’t believe that her faith is warranted, but even if it were that wouldn’t be enough to make this system benign.

  ‘As I speak, many of you – I hope – are still struggling to decide how you’ll vote on this question. And when the result is declared, that will surely be a public matter. The announcement won’t be an invasion of anyone’s privacy, an act of libel, or anything else that could fairly or sensibly be punished. And yet if you’d known the result in advance, wouldn’t you feel that your own personal decision-making process had been altered? Of course you’d still be free to vote in accordance with your wishes, but the whole sequence of contesting thoughts – all the private debates inside your own skull that led you to that final action – would be playing out in a very different context.’

  Ramiro checked the timer; he was still less than halfway through his quota, but he was not going to let himself get cut off again.

  ‘Knowing even the most mundane facts from the public record will crush our political lives, flattening our inner dialogues into a choice between impotent rage and apathetic conformity. Of course we’re accustomed to being helpless after the fact to reverse a vote that goes against us, but remember: the results of elections and referenda that we know in advance will not be guaranteed to be the same as they would have been in the absence of foreknowledge. We won’t be hearing about a future that would have happened regardless – as every proponent of this system will affirm, because if that were true it could never yield any benefits. Rather, we’ll be reshaping the whole process by which we make decisions – at the political level without a doubt, but I believe that the same kind of distortion will afflict every aspect of our lives.’