---
title: "Time, Clocks, and the Ordering of Events in a Distributed System"
description: "Lamport asks how separated computers can agree on a useful event order when no perfect global clock tells them what happened first. Read it to see how local event order and delivered messages define causality, how message-carried logical counters preserve that order, and why the resulting timestamps still cannot prove that two events influenced one another."
canonical_url: "https://fanout.sh/daily/2026-09-11-lamport-logical-clocks"
md_url: "https://fanout.sh/daily/2026-09-11-lamport-logical-clocks.md"
last_updated: "2026-09-11"
access: "public"
---

# Time, Clocks, and the Ordering of Events in a Distributed System

Lamport asks how separated computers can agree on a useful event order when no perfect global clock tells them what happened first. Read it to see how local event order and delivered messages define causality, how message-carried logical counters preserve that order, and why the resulting timestamps still cannot prove that two events influenced one another.

## Paper details

- Authors: Leslie Lamport

- Venue: Communications of the ACM 1978

- Track: Systems

- Difficulty: Easy

- Reading time: 30 min

- Original paper: https://lamport.azurewebsites.net/pubs/time-clocks.pdf

## What you will learn

- How same-process order, message send before receive, and transitivity define the happened-before partial order while unrelated events remain concurrent.

- Why each process increments a logical counter and advances it beyond a received timestamp before recording the receive event.

- How a fixed tie-breaker extends causality to a useful but arbitrary total order, and which delivery, participation, external-causality, and physical-time limits remain.

## Continue exploring

[Explore clocks and ordering in Fanout](https://fanout.sh/system/archive/clocks-and-ordering): Connect Lamport's logical clock to Fanout's practical guide for wall clocks, monotonic time, version vectors, consensus logs, time-sortable IDs, and correctness-sensitive ordering.

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