B1.5 · dive — the 41-bit horizon
September 2093, recorded.
The layout grants 41 bits of milliseconds above a 2024-01-01 epoch
(1704067200000); 2⁴¹ milliseconds is about 69.7 years, so the timestamp field
exhausts in September 2093. The horizon is recorded here rather than discovered later — seventy
years is enough runway to make the successor epoch a planned chapter, never an incident.
Source: content/bcs1.5.md · What and Decisions; the epoch and the layout are the contract’s (content/vectors.json: epoch_ms, timestamp_bits).
1704067200000 (2024-01-01) is about
69.7 years; the field exhausts in September 2093; the successor epoch is a contract amendment with a
wire-version bump and a drain-and-switch lane — a planned chapter, never an incident.The arithmetic, stated plainly
content/bcs1.5.md · What41 bits of milliseconds above 1704067200000. 2⁴¹ milliseconds
is about 69.7 years. The field exhausts in September 2093. Nothing here is an estimate of load or a
guess about growth — the horizon is a property of the layout, computable on the day the contract was
signed, and the contract carries the inputs:
epoch_ms 1704067200000 -- 2024-01-01T00:00:00Z
timestamp_bits 41
node_bits 10
sequence_bits 12
The order theorem of Chapter 1.2 makes the same bits do double duty: because the timestamp rides in the high bits, string order is time order, and every page of this course leans on that. The horizon is the other side of the same grant — a field this useful is a field with an end, and an architecture that quotes its measurements records its expiry date in the same ledger.
The field, consumed
computed from the contract’s constantsThree checkpoints, all from committed sources: the epoch itself, the canonical decode
vector’s millisecond (1780512970164 — read from USR0NgWEfAEJfs in
vectors.json), and the field’s last millisecond (2⁴¹ − 1 above the
epoch). The readout computes milliseconds above the epoch and the share of the 41-bit field consumed —
pure BigInt arithmetic over the contract’s constants.
The successor epoch, planned
content/bcs1.5.md · DecisionsA successor epoch is a contract amendment with a wire-version bump and a drain-and-switch lane — the same shape the EchoMQ migration already uses. The decision of record: the horizon is 2093 and recorded; the successor epoch is a planned amendment riding the existing wire-version lane, not an emergency.
That is the whole point of recording the horizon on signing day. An architecture that discovers its timestamp field in a production incident writes the amendment under duress; an architecture that records the date in Part I writes it as a chapter, seventy years early, with the lane already proven by a different migration.
The migration lane
Versioned wire formats, the drain-and-switch shape, and the two-way fence — the bus protocol the successor epoch would ride, taught in depth.
The layout’s owner
B1.2 — the contract that owns the epoch, the 41/10/12 split, and the minting law the horizon is computed from.
The measured chooser
B1.3 — the storage record where the same layout is priced per key against every rival format.
References
sources · relatedSources
- Lamport — Time, Clocks, and the Ordering of Events in a Distributed Systemthe foundation the next dive stands on
- Valkey documentation — Streams introductionstream entry ids carry the millisecond; the same range arithmetic
Related
- B1.5 — The Time Inside the Namethe module hub; the three clocks in context
- B1.2 — The Identity Contractthe layout and the minting law
- EchoMQ — the coursethe migration lane the successor epoch rides