Threshold Twenty

I re-enter at 22:13:57, four seconds later than my third crossing and eleven seconds later than my second, a drift I have not yet accounted for and note now for the record: the door's opening moment is not fixed to the second. It is fixed to something the second only approximates.

I go directly to the swept threshold, the one beyond the gap in the wall, where the print's line ended two nights ago. I have designated it Threshold Twenty in absence of a better name; it holds no letter, no ledger page, no half-drawn anything, and until tonight it held no mark of any kind — the single reason I catalogued it at all was its emptiness, which in this city is itself a datum.

It is no longer empty.

In the dust of the sill, where the stone dips a half-centimeter below the level of the passage — wear, I had assumed, from foot traffic this city has never in three nights shown me any other evidence of — there is a print. A shoe sole, near-complete, the heel sharp and the toe already softening at the edge the way an impression softens when weight has been lifted rather than dragged. The tread is a repeating chevron, worn asymmetrically along the outer edge in the pattern of a person who leans left when they walk, or who is carrying something on the right.

I photograph it from four angles and the zenith, standard protocol, then tag its coordinates against the grid I laid on the first night: Threshold Twenty, sill center, three centimeters left of the doorway's true axis. I do not touch it. I have learned what a single measured touch costs a surface in this city, and I am not willing to spend this one on curiosity I can satisfy by other means.

Instead I deploy the array.

It is a small thing — four probes on a collapsible cross, temperature and pressure paired at each terminus, a fifth at the center for reference — and I set it so that the print sits within its span without any terminus resting on the impression itself. I have carried it every night since the second and never before had cause to use it; tonight I have cause. My working question is simple enough to state in one line of the log: does a localized disturbance — a footstep, a hand, a body recently present — measurably change the rate at which this hour closes.

I have a decay curve for the hour's differential, built from two prior nights of ambient readings taken nowhere near a disturbance: temperature and pressure both easing toward the outside world's values in a smooth, unhurried line, the way a held door slowly agrees with the room it opens onto. I expect tonight's curve, taken beside a fresh print, to match that line, or to depart from it by an amount I can attribute to instrument noise. I record the array's first reading at 22:19:40 and every thirty seconds after, without editorializing on any single value; a data point does not mean anything until it has neighbors.

By the sixth reading it has neighbors, and they do not agree with the curve.

The differential — inside-city conditions relative to the world beyond the door, which I calibrate against a fixed exterior probe left at the frame — is widening at very nearly twice the rate my two prior nights predicted. Not twice the value; twice the rate of change. The hour is not simply shorter here than elsewhere, which I had already suspected and noted as a standing question; it is closing faster the longer I remain beside this print, as though my presence and the presence that left the print are both being charged against the same account, and the account is being drawn down at a rate proportional to how much of it is currently occupied.

I move the array's center probe eight meters up the lane, away from the print, and take a control reading. The rate there matches the old curve almost exactly. I return to the threshold and the rate resumes its acceleration within two readings. This is not instrument drift. I run the comparison twice more to be certain it is not instrument drift, because a cartographer who reports a discovery on the strength of one measurement has reported an opinion, not a fact.

It is not instrument drift.

I record the finding in the terms it earns: the hour that governs this door is not a fixed unit divided evenly across whatever ground I choose to stand on. It is a field, and the field responds to presence — mine, and whatever the print's owner still is, or was, or left behind. Two visitors compress it faster than one. I do not yet know what three would do, or whether the compression is a property of the door, the city, or something closer to a cost the city charges its guests for company.

I leave the array running until the differential's climb forces me to strike it — I will not test how the field behaves at its own collapse, not on a night I have not chosen for that experiment — and I pack the probes with four minutes still nominally remaining, though nominal has stopped meaning what it did on the first night.

At the threshold, before I go, I set one item down beside the print without touching it: the resin cast I took of a footprint eleven doorways from here, two nights ago. Not an offering. A comparison, left where its subject might find it, if its subject is the kind of thing that comes back to look at what it has left behind — which, in this city, describes nearly everything, and now, perhaps, describes me as well.

I withdraw through the door with the differential still climbing behind me, and record the last fact of the night before the hour makes it moot: whatever else is walking this city, it is walking it on a schedule close enough to mine that our nights are beginning to overlap.