First Through The Games Master's Guide Contents The Players' Guide PDF

Background

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The Physics, Exactly

You will be asked about this by a player who is paying attention, and the answers need to be the same every time, because the plot of the whole campaign is a consequence of them.

Transit is zero

Instantaneous. Not fast — zero. Step onto the plate and you are at the other end, and the only reason you know is that the air is different.

What can take time is the door agreeing to open. That is a separate thing, it is normally too small to notice, and when it becomes measurable it is the single most frightening thing in this setting. See The Hesitation.

Only matter crosses, and only a person carries it

No light, no signal, no radio, no data, no cargo that nobody is holding. A person, and what that person has on them.

Inside a system, radio works perfectly normally. Two stations round the same star talk four times a day. Players and Games Masters alike forget this, and it is load-bearing: at Gliese 65 the refinery can warn Ladder by radio in ten and a half minutes, and cannot warn Sirius at all.

And therefore nobody can reach you. A handler briefs on this side and cannot follow, cannot call, cannot send help, cannot change the order. That is why a fifteen-year-old’s judgement is the whole safety system, and it is why this campaign gives the player real decisions instead of instructions.

A mouth is pinned to a potential, not to a place

The load-bearing sentence of the entire setting.

A door’s far mouth sits wherever a particular value of gravitational potential currently is. Mostly the matching surface drifts a few metres in a century. A stray happens when the sum has more than one answer and the mouth jumps to a different one.

Two consequences the players will meet:

Straying is predictable, because potentials reshape with orbits. Nobody knows this. See the previous chapter.

A door can move somewhere useful. In Act One it does. The disaster and the rescue are the same event, and that is the shape of the act.

What a crossing costs

Fraying: small, cumulative, irreversible, and visible on the weave. Finished at about twenty-two. Carrying an adult costs the carrier a fortnight off the end of their life, counted; a child costs minutes. Three or four adult carries in a row finishes anybody.

Never round these down at the table and never let a Non-Player Character be vague about them. The cost being exact and spoken aloud is what makes Act One’s turn land.

Twenty years to the light year

The seedships fly at a twentieth of lightspeed, so a door opens twenty years per light year after launch. Launch was nine hundred and seventy-five years ago. That one sum fixes the entire map and the entire calendar — change it and every date in the campaign is wrong.

The frontier is therefore a sphere a little under forty-nine light years out, advancing one light year every twenty years.

And here is what that produces

Every star on this sheet is at its true galactic position, computed from the measured parallax in data/systems.json, and every line on it is a real edge out of data/edges.json. It is rendered by maps/causeway_chart.py, so it cannot disagree with the campaign — regenerate it rather than editing it.

Read it as a graph, not a volume, which is the single hardest idea in this setting to get a player to hold. Distance tells you what a telescope says. It tells you nothing about how long it takes to get anywhere. What matters is whether there is a line.

On screen every star name is a link to its Wikipedia article. That is not decoration: it is the whole claim of this chapter made checkable by a fifteen-year-old in four seconds, and you should let them do it.

The Causeway — the known network, 975 years after the Reach THE CAUSEWAY THE KNOWN NETWORK, 975 YEARS AFTER THE REACH 28 SYSTEMS · 26 DOORS · ONE HUMANITY 10 20 30 40 48.75 LY THE FRONTIER 10 LIGHT YEARS GALACTIC CENTRE PLATE I. THE WHOLE NETWORK RADIUS 48.75 LIGHT YEARS GALACTIC PLANE IN PERSPECTIVE, ELEVATION 20° POSITIONS COMPUTED FROM SIMBAD PARALLAXES TRAPPIST-1 HD 69830 55 CANCRI HD 40307 GJ 1214 LHS 1140 NOT YET OPEN SEE PLATE II 5 10 15 17 LY GL 725 (STRUVE 2398) BARNARD'S STAR 61 CYGNI EPSILON INDI GLIESE 887 GLIESE 876 VAN MAANEN'S STAR ROSS 128 WOLF 359 LALANDE 21185 WISE 0855-0714 LUHMAN 16 ALPHA CENTAURI PROCYON SOL SIRIUS KAPTEYN'S STAR GLIESE 65 EPSILON ERIDANI TEEGARDEN'S STAR TAU CETI YZ CETI 40 ERIDANI 5 LIGHT YEARS GALACTIC CENTRE PLATE II. THE INNER REACH RADIUS 17 LIGHT YEARS — 23 OF THE 29 SYSTEMS OUTER RING 17 LIGHT YEARS — NOT THE FRONTIER HEAVY LINES ARE THE NINE, THE DOORS MEETING AT SIRIUS CONVENTIONS System, door open System, door not yet open System, door dark — strayed into rock Dropline to the galactic plane Door — bidirectional Door midpoint The Nine — Sirius's nine doors THE TWENTY-NINE SYSTEMS Sol 0.00 Alpha Centauri 4.39 Barnard's Star 5.96 Luhman 16 6.50 WISE 0855-0714 7.43 Wolf 359 7.86 Lalande 21185 8.30 Sirius 8.60 Gliese 65 8.87 Epsilon Eridani 10.50 Gliese 887 10.72 Ross 128 11.01 61 Cygni 11.40 Procyon 11.46 Gl 725 (Struve 2398) 11.49 Epsilon Indi 11.87 Tau Ceti 11.91 YZ Ceti 12.12 Teegarden's Star 12.50 Kapteyn's Star 12.83 van Maanen's Star 14.07 Gliese 876 15.24 40 Eridani 16.34 TRAPPIST-1 40.66 HD 69830 41.03 55 Cancri 41.05 HD 40307 42.18 GJ 1214 47.75 LHS 1140 48.80 Distances in light years from Sol, computed from SIMBAD parallaxes. On screen, every star name links to its Wikipedia article.
THE CAUSEWAY — THE KNOWN NETWORK, 975 YEARS AFTER THE REACH — open the full sheet

The reference entries

How an Anchor Works

An anchor is half of a pair, and the pair is entangled — made together, in the same place, at the same moment, and bound at a level nothing since has been able to reach into.

That single fact decides almost everything about the world you live in.

They are married for life

A mouth is bound to its own mate and to nothing else, ever. You cannot re-point one. You cannot introduce an anchor to a different anchor and talk them into it. You cannot cut a pair in half and make two new routes out of the pieces; people have tried, with everything from arc furnaces to centuries of patience, and all they have ever produced is scrap and two dead mouths.

So a door is not a technology anybody owns. It is a marriage, and there are only as many as the Reach made.

Matter crosses. Nothing else does, and never will.

Walk at the housing and you arrive. No tunnel, no transit time, no distance in any sense you could measure.

Now put a radio against it and shout.

Nothing happens, and nothing ever can. Entanglement by itself carries no information — that is not a limit of our instruments, it is a theorem, proved before the Reach launched and never dented since. The correlation is perfect and it cannot be used to say anything. Light still crawls, every signal still obeys it, and the door is no help at all.

Which is the whole shape of human civilisation. There is no telemetry, no warning, no calling through, no listening in. If you want something known on the other side of a door, a person carries it, in their arms, one at a time. See What Crosses Easily.

It also means no door has ever been eavesdropped on. There is nothing to tap. A thing said at the Nine is known at the Nine, and arrives anywhere else in the company of whoever decided to walk it there.

What the crossing does to you

The mouth does not move you. It takes what you are, holds it, and lays it down again at the mate — and the laying down is very good and not perfect. The error is small, it never comes out again, and it is why only the young can cross and where the knacks come from. See What a Crossing Does.

And it does not do any of this by itself. A door is not a door until a first-through is standing in it, holding the crossing open while it happens.

What a first-through can actually repair

Housings foul. Collars creep. Load beds drift and start fighting themselves. Those are maintenance and a competent fifteen-year-old with a toolroll handles all three.

What nobody can do is build one, pair one, re-point one, or persuade a mouth to be anywhere other than where the physics has put it — which brings us to Straying.

The Hesitation

Transit is zero. It has always been zero, it is zero on every door in human space, and nothing in this entry changes that. Step, and you are there, and the only reason you know you crossed is that the air is different.

What can take time is the door agreeing to open.

Why

A mouth is pinned to a gravitational potential and sits wherever that value currently is. See Straying. Mostly the matching surface drifts a few metres in a century and nobody writes anything down.

A stray happens when the sum has more than one answer and the mouth jumps to a different one.

What nobody had measured until now is what a mouth does in the weeks before that — while the sum is becoming ambiguous and has not yet resolved. It cannot settle. It is pinned to a value that two places now satisfy, and it spends a while being unable to choose.

And a mouth that cannot choose will not establish a throat on demand.

What it is like

You step up and give it your weight and nothing happens.

Not a push-back. Not resistance. It goes absolute, the way a wall is absolute, and every first-through in the Causeway already has a word for it because it happens for a dozen harmless reasons in an ordinary career: it sets.

Then you ease off, and offer it again, and after a moment it takes you — and the crossing itself is instantaneous, exactly as it has always been.

The thing to measure is the moment: how long you stand in a lit housing before it will have you.

The number, and why nobody had it

For nine hundred and seventy-five years the number was a fraction of a second on a bad day and nobody could have measured it if they had wanted to, because

  • a clock is not alive and cannot cross, so there are no instruments in a housing beyond what the station can see from outside, and
  • nobody had any reason to time a thing that has always been instant.

So it was folklore. Seven’s sticky this week. You want to give it a second. Every deck has a door with a reputation and nobody ever wrote the reputation down.

The first instrumented series was taken at the Nine on door seven, by a fifteen-year-old holding a tempo built into her head, with a glint counting independently beside her, because a station mind could time the housing’s draw from outside and could not time the hesitation from the inside of it.

What it means when it rises

A rising hesitation is a mouth running out of ways to be in one place.

It is the only advance warning of a stray that anybody has ever had, and it was sitting in the folklore of every deck in the Causeway for nine centuries, unwritten, because the people who felt it were children and the thing they felt was an inconvenience.

Nobody knows how long the warning is. Hours, weeks, a year. There is no second case to compare with, which is the entire argument for a funded study and the entire reason there has never been one.

What it is not

  • It is not damage. Doors do not break and this is not the beginning of one breaking. See Straying.
  • It is not a place. There is no interval you are inside, nothing to see, and nothing in there with you. You are standing in a housing on the near side the whole time.
  • But standing in an unsettled housing is not nothing. The field has a real gradient with a fixed geometry, and six months of standing in it twice a watch leaves a mark. See The Cold Arm.