---
id: media/mirror-worlds
about:
  label: Mirror Worlds
  description: >-
    David Gelernter's 1991 book that first described software models of real
    places and institutions, fed by live data, that anyone could look into; the
    idea the digital twin of a place grows from.
  tags:
    - origin
    - mirror world
    - software
    - city
    - history
  depiction: cover.jpg
book:
  authors:
    - David Gelernter
  publisher: Oxford University Press
  year: 1991
  isbn: '9780195079067'
  url: 'https://openlibrary.org/works/OL937468W'
domains:
  - places
relations:
  - predicate: made_by
    target: people/david-gelernter
provenance:
  origin: agent
  sources:
    - title: >-
        Mirror Worlds, Or, The Day Software Puts the Universe in a Shoebox--:
        How it ... - David Hillel Gelernter - Google Books
      url: 'https://books.google.com/books?vid=ISBN9780195079067'
    - title: 'Open Library: Mirror worlds'
      url: 'https://openlibrary.org/works/OL937468W'
  created: '2026-10-17'
  reviewed: '2026-10-17'
  reviewed_by: 'Claude, from the sources listed'
  status: draft
---
[Gelernter](/people/david-gelernter/), a computer scientist at Yale, argued that small programs were about to be joined by large public software works. The most important would be the Mirror World, a running model of a real place, such as a city, or of an organisation. Fed by a stream of live data, it would show the state of the whole at this moment. Readers could look in, move around, ask questions and try out changes.

Part of the book covers uses, such as running a hospital or following a city council. Part covers how a Mirror World could be built from the technology of the time, explained through everyday analogies. The book was first published in 1991, and the paperback followed in 1992.

Most of what the field now calls a twin is set out here, decades before the term existed: the live feed, the model of the whole, and what-if questions.

Cover via Open Library.