§ Greg egan: Orthogonal

I found the idea of writing a story about a universe with a closed loop of time fascinating. Here are some of the sentences that really helped me "get" compatiblism as an idea thanks to reading the book:

Suppose we leave a piece of equipment behind on Esilio - say, a
small spyglass. Over the eons, from our point of view, we'd expect it to become
pitted by dust in the wind, and eventually break up completely and turn to
sand. Our spyglass, our rules: that sounds fair, doesn't it? But if that sand
stays on Esilio, what origin will it have from Esilio's point of view? Most
likely, some ordinary Esilian rock will have broken down to make it - which to
us, would look like erosion running backwards. But then, in Esilian time the
remnants of that rock will eventually form themselves spontaneously into a
spyglass, which lies on the ground until we come along to retrieve it. So if
you follow the history of the matter that makes up the spyglass far enough in
both directions, it's clear that it's not committed to either side's rdes.'

'Swap the roles of Esilio and the Surveyor,' he replied, 'then tell the same
story again. If something from Esilio takes the place of the spyglass, it must
be with us already. We must have been carrying it, or the things that will
become it, from the very start. Because according to Esilio's arrow of time
we've already visited the planet, and it's almost certain that something
remained with us when we departed.'

'Tell us one thing that you're sure won't happen,' he challenged her. She
said, 'Two objects in thermal contact will not maintain different
temperatures over a long period of time.' 'Because ... ?' 'Because there are
vastly more possibilities in which they share their thermal energy more
equally. If you pick a possibility at random, it's likely to be one of those.
Fundamental physics might make the entropy minimum necessary - but we still
expect the cosmos to be as random as it can be.'

There was fine red dust covering the grey hardstone walls of the airlock. He
hadn't noticed it by the dimmer illumination of the safety light. He ran a
gloved finger along the seal of the outer door, trying to find the point
where it had been breached, but if there was a hole it wasn't apparent. It
hardly mattered now; however the dust had entered, he was about to let in a
great deal more. But as he began to turn the crank, the realisation hit him:
it hadn't corne from outside. They must have brought it with them all the way
from the Peerless, scattered invisibly throughout the craft, with a little
more accumulating inside the airlock each time the inner door was opened. Or
in Esilio's terms: the Surveyor's visit had just ended, and this residue was
something they would soon take away with them

Twice, as she jumped out of some indentation in the sand, it vanished. She
and Azelio hadn't actually made all the tracks that he'd attributed to them.
Or not yet, they hadn't. 'Come and join us,' Azelio said. 'Some of these
must be yours.'

Each time Azelio lifted his feet, scattered sand unscattered itself, grains
sliding in around the places where he'd stepped to settle more evenly -
though not always smoothing the ground completely. After all, 197 Ramiro
reasoned, it was possible to walk in someone else's footprints, or to step
several times in your own. It would only be the last footfall on any given
spot - prior to the next occasion on which the wind levelled everything -
that would unmake the imprint completely.

'What happens if I try to walk on pristine ground?' he asked. 'Try it and
see!' Agata taunted him. Ramiro descended to the bottom of the ladder,
intending to move quickly and get the ordeal over with, but then his resolve
deserted him. When he willed his foot to land on unblemished sand, what
exactly would intervene to stop him? A cramp in the muscle, diverting his leg
to its proper, predestined target? A puppet-like manipulation of his body by
some unseen force too strong to resist, or a trance-like suspension of his
whole sense of self? He wasn't sure that he wanted to know the answer. And
perhaps that was the simplest resolution: he would lack the courage to walk
out across the surface of Esilio for the rest of the mission. He would cower
in his room, leaving the work to the others, while he waited to return to the
Peerless in disgrace.

He'd scrutinised the ground beforehand, and he was sure there'd been no
footprints at all where his feet now stood. He lifted one foot and inspected
the sand below. He had created an indentation that had not been there before.
That was every bit as strange to Esilio as the erasures he'd witnessed were
strange to him.

'How?' he demanded, more confused than relieved. 'You
really don't listen to me, do you?' Agata chided him. 'Did I ever tell you
that the local arrow was inviolable? 'No.' What she'd stressed most of all
was a loss of predictability but the sight of her and Azelio unmaking their
footprints had crowded everything else out of his mind. Those disappearing
marks 198 in the sand might be unsettling, but if he could ignore them and
walk wherever he pleased then they were not the shackles he'd taken them to
be.

'What happens if there are footprints that no one gets around to
before the next dust storm?' he asked Agata. 'Ones that were there
straight after the last storm?'
She said, 'There can't be a footprint untouched by any foot. I don't
understand the dynamics of wind and sand well enough to swear to
you that there won't be hollows in the ground that come and go of
their own accord - but if you're talking about a clear imprint, if we
could keep our feet away from it, it simply wouldn't be there.'

Esilio was a world where a certain amount of nOiSY, partial - and
predominantly trivial - information about the future would be strewn across
the landscape. There had always been plenty of trivial things that could be
predicted with near-certainty back on the Peerless, and perhaps as many of
them would be lost, here, as these eerie new portents would be gained

Emboldened, he strode out across the illuminated ground, pausing
every few steps to kick at the sand. Sometimes he simply pushed the
dust aside; sometimes the dust applied pressure of its own, as it
moved in to occupy the space his foot vacated. But that pressure
never came out of nowhere: his feet moved as and when he'd willed
them to move, followed by the dust but never forced to retreat. Nor
were they thrust without warning into the air

Each time there was a dust storm the record of future movements would be
erased, but even in a prolonged period of calm the footprints would overlap,
conveying very little information.

'You already dug twelve holes!' he observed.
'And I thought you were messing around with Agata all morning.'
Azelio made a noncommittal sound.
'My plan is to dig up all these plants at the end of the trial and take
them back to the Peerless for my colleagues to analyse,' Azelio mused. 'So I
guess that's when I'll see the transition between cultivated and truly
pristine ground. But right now, in Esilio's terms, we've just dug the plants
up - so on our terms, we're about to do that. Backwards.' Ramiro said, 'You
make it sound as if you've been practising timereversed agronomy all your
life.' 'It's not that hard to see what's going on, if you think it through,'
Azelio replied lightly. 'But you don't mind following markers like this?
Evidence of acts you haven't performed yet?' 'It's a little disconcerting,'
Azelio conceded. 'But I can't say that it fills me with claustrophobia to
know that I'll carry out the experimental protocols I always planned to carry
out.'

He lowered the plant until its roots were in the hole, then
he started adding soil from the surrounding mound. Some of the soil
was scooped in with pressure from behind, in the ordinary manner.
Some appeared to pursue the trowel, the way the dust sometimes
pursued Ramiro's feet. What decided between the two? Azelio's own
actions had to be consistent with the motion of the soil, but which
determined which? Maybe there was no answer to that, short of the
impossible act of solving in the finest detail the equations that Agata
was yet to discover, revealing exactly which sequences of events
were consistent with the laws of physics all the way around the
cosmos.

Ramiro's left arm had grown tired from holding the plant in place over the
hole. He shifted it slightly to make himself more comfortable, but as he
shifted it back he saw soil rising and adhering to the roots. He stared at
this bizarre result for a moment, then decided to stop wasting time delaying
an outcome he had no wish to oppose. He held the trowel to the side of the
mound nearest the hole, then drew it closer. The sand followed the blade -
not adhering to it and needing to be brought along, but gently pushing it. He
lowered the trowel into the hole then withdrew it; the sand parted from the
blade and packed itself between the roots of the plant and the side of the
hole.

He hesitated, groping for a clearer sense of his role in the task. But
what could he actually do wrong? So long as he was committed to
making whatever movements with the trowel were necessary until
the plant was securely in place, that state of mind and the strictures
of the environment ought to work it out between themselves.
He scooped some soil straight into the hole; like the last delivery, it
clung to the roots. In Esilio's terms, this soil had spent at least a few
stints packed tightly around the plant; if he could have seen the
action in reverse, it would have involved nothing stranger than a
clump of sand finally coming loose.

But as she moved the broom across the floor, duly concentrating the dust
ahead of it, other dust began to appear behind it - some of it falling from
the air, some sliding over the stone to pile up against the bristles. Its
entropy was decreasing too, as it accumulated from whatever scattered reaches
of the Surveyor in which it had been lurking. The net result was that the
stretch of floor she'd swept remained as dusty as ever.

But the plants' uptake of nutrients relied on interactions
between their roots and the native soil at a microscopic level, and
there was no guarantee that the two systems, left to themselves,
would simply sort out their differences

'Because the test plots are failing,' Agata explained. 'So we need
to take the explosive up into the hills, turn some rock into soil for
ourselves - against the Esilian arrow - and see if that imbues the soil
with the properties that it needs to support plant growth

'If we do set off this
explosive,' he reasoned, 'shouldn't we be able to see some evidence of
that already?'
Agata said, 'You mean a crater?'
'Yes.'
'If we found a site like that, it would be useless to us. It would imply
that after we set off the bomb, the crater would be gone and the sand
around it would be rock again.'
Ramiro scowled. 'Esilio doesn't care what's useful or useless, or it
wouldn't have killed the plants, would it?'
'Esilio doesn't care,' Agata agreed, 'but why would we go ahead and
set off the bomb there, knowing that it would do us no good?'
'Because the crater would prove that we did!' Ramiro replied heatedly.
'But as far as we know, there is no such crater.' Agata met his gaze
openly, trying to reassure him of her Sincerity: she wasn't playing
some verbal game just to annoy him. 'There is no crater, because if
we saw it, we wouldn't choose to make it. Esilio can't force our hand;
whatever happens has to be consistent with everything, including
our motives. Ramiro said, 'It can't force our hand, but there could still be an
accident.' 'That's true. But if we saw such a crater, we wouldn't even go near it
with the explosive.'

He ran a hand over his face. 'If the plants can't
bring their arrow to Esilio, why should a bomb do any better?'
'The roots of a plant aren't entirely passive,' Azelio replied, 'but
they do rely on the state of the soil. I don't think the bomb going off
will rely on anything like that.'
'But in Esilian time,' Ramiro protested, 'all the soil we're supposedly going to make with this bomb has to mesh perfectly with a
backwards explOSion in such a way that it forms a solid rock. How
likely is that?'
How likely are the alternatives?' Agata countered. 'How likely is
it that the explOSive will fail to detonate? How likely is it that we'll
allow it to explode in an existing crater instead - just to pander to
Esilio's arrow?'

She started swinging her pick into the rock face.
Small chips of stone flew out from the point of impact, stinging her
forearms, but the rush of power and freedom she felt at the sight of
the growing excavation was more than enough to compensate.
In Esilian time, the chips were rising from the ground, propelled into
the air by conspiracies of time-reversed thermal diffusion, just to aid
her as she rebuilt the rock. What stronger proof could there be that
the cosmos had a place for her, with all her plans and choices? One
day it would kill her, but until then the contract was clear: hardship
and frustration and failure were all pOSSible, but she would never be
robbed of her will entirely.

the lines on the
rock face formed symbols. The sides of the ridges appeared softened
and eroded, as if a generation's worth of future dust storms had left
their mark. But she could still make out most of the message.
' ... came here from the home world,' she read. 'To offer thanks
and bring you ... courage.'
Azelia said, 'Who thanks whom for what?'
'It's from the ancestors,' she said. 'They're going to come here and
write this. They're going to come here to tell us that everything we've
done and everything we've been through was worth it in the end.'

But ever since he'd seen the writing for himself, he'd been unable to stop
wondering if the message suited him too well. As far as he could recall, he'd
never consciously planned to commit any kind of hoax. What he didn't know was
exactly what his lack of preparation meant. The words were there, nothing could
change that now. But with every moment that passed it seemed more likely to him
that the ancestors had nothing to do with it, and that he would find a way to
write the message himself.

To feel alive, he needed to feel himself struggling moment by
moment to shape his own history. It was not enough to look down
on events from above like a biologist watching a worm in a maze,
content to note that this creature's actions had never actually gone
against its wishes.

nothing helped a plan run more smoothly than having a law of physics on its side

How could he carve anything into the rock face, if the idea of doing
it had only come to him after he'd seen the result? Even the choice
of words hadn't sounded like his own. If he'd only selected them
because he'd read them, who would have made the choice? No one.
Agata had told him endlessly: a loop could never contain complexity
with no antecedent but itself, because the probability would be far
too low. There could be no words appearing on rocks for no other
reason than the fact that they'd done so.

'We've all hit a dead patch,' Lila said sadly. 'Chemists, biologists,
astronomers, engineers. Since they switched on the messaging
system, there hasn't been a single new idea across the mountain.'
'You mean no one's been sending back new ideas?' Agata had
predicted as much - but surely that self-censorship hadn't surprised
anyone.
'Oh, the messages have contained no innovations,' Lila confirmed.
'But neither has the work itself.'
'I don't understand,' Agata admitted.
Lila said, 'If people did innovate, the results would leak back to
them one way or another. I know you believed that they'd be able
to keep qUiet, so everything would go on as usual. But everything
has not gone on as usual. We've had no new ideas since the system
was turned on - because if we'd had them, we would have heard of
them before we'd had a chance to think of them ourselves. The
barriers to information flow are so porous now that the knowledge
gradient has been flattened: the past contains everything the future
contains ... which means the future contains nothing more than
the past.'

What would her own generation be famous for? Rendering
the creation of new knowledge impossible.

'I'm where I need to be.' 'In the administrative sense, or the teleological?'

Azelio hummed with frustration. 'What's all this talk of replacement? If a
meteor is going to hit us, it's going to hit us! You can devise as many
ingenious plans as you like to try to sabotage the system at the very same
moment, but if there's a rock on its way, nothing you do is going to make it
disappear.' 'If there's a rock on its way, that's true,' Ramiro conceded.
'But until we know that there is, why should we assume that? The history of
the next twelve stints ends with the messaging system failing; we're about as
certain of that as we can be. Some sequence of events has to fill the gap
between that certainty and all the other things we know. So which snippets
would you rather the cosmos had on hand to complete the story? Just one,
where a meteor hits the Peerless? Just two: a meteor, or a bomb? Making our
own preferred version possible won't rule out everything else - but if we
don't even try, we'll rule out our own best hope entirely.'

Azelio was looking disoriented. 'I want this to work,' he said
haltingly. 'But every time I stop and think about it, it feels as if all
we're doing is playing some kind of game.

Azelio glanced down at the pile of notes on her desk. 'And doesn't
everything that could happen, happen? Isn't that what your diagram
calculus says?'
'No.' Agata nodded at the pile. 'Por a start, you can only add up
diagrams that begin and end in exactly the same way: they all take
different paths, but their end pOints have to be identical. Getting
to the disruption with benign sabotage leaves the mountain intact;
getting there with a meteor strike hardly brings you to the same state.
And even when the end points are identical, all the alternatives you
draw for a process just help you find the probability that the process
takes place. Those alternatives don't all get to happen, themselves.'
'Then what makes the choice?' Azelio pressed her. 'When a luxagen
could end up in either of two places, how does just one get picked?

Just because
we don't know the cause of the disruption, that doesn't mean that every cause
we can imagine will coexist. If you want history to unfold a certain way,
forget about wave mechanics. What matters now are the usual things: who we are,
what we do, and a certain amount of dumb luck.'

Azelio put the diagram down. 'So if there's a meteor coming, how
do I stop it? Or avoid it?'
'You can't,' Agata replied. This was the sticking point they always
reached. 'Not if the disruption is the proof that it hits us.'
'Then what difference does it make "who we are" and "what we
do"?' Azelio asked bitterly. 'If I go through the motions of enacting
something more benign ... how will that help? If there's a murderer
trying to kill your family, you don't protect them by moving your
own tympanum to match the threats being shouted through the
door. Or do you really believe in safety through reverse ventriloquism?'
Agata wrapped her arms around her head in frustration. 'We don't
know that there's a murderer at the door! We don't know that there's a
meteor on its way!'

'This is your pass,' the woman
explained, handing her a red disc. 'Please don't lose it.'
'Do I lose it?' Agata asked.
'Of course you don't,' the guard replied. 'Because I asked you not
to.' 'Right.' Agata suppressed a shiver.

'I didn't make the inscription,' Tarquinia declared. 'I went out there to try,
but nothing happened: no shards of stone rose from the ground to meet the
chisel. I tried different tools, different movements ... but I couldn't unwrite
those symbols. If anything, when I left they were sharper than I'd found them -
as if all I'd done was make the message less clear for Agata and Azelio than if
I'd stayed away completely. I wasn't the author of those words. Someone else
must be responsible for them.'

I wish I could talk to them,' she said. 'I wish I could thank
them. I wish I could tell them that it wasn't for nothing, that it ended
well.' Clara said, 'If that's what you want, then I believe you'll find a
way.'