# universe (0000-universe.com)

The universe is everything that exists: all of space, time, matter, and energy. People say it to mean the whole cosmos, or sometimes a particular world or domain they care about, like "the Marvel universe" or "my universe."

## What a model may hear
- database of all possible facts (formal logic and AI knowledge representation): treat the word as a bounded set of all propositions under discussion, and may limit answers to that closed world
- set of all elements in a type system (type theory and programming languages): assume a universal quantification over every value of a type, or check that something holds for all cases
- single simulation or game world (game development and simulations): load or generate one specific instance of a world with its own physics, rules, and state
- complete collection of data (statistics and data science): take the word to mean a full population rather than a sample, changing what methods apply
- universal set in set theory (mathematics): invoke axioms about sets that contain everything, which can lead to paradoxes if handled naively

## Where people and models part ways
- Says: "Tell me about the origin of the universe"
  Means: the Big Bang and cosmology
  May be taken as: return a formal definition of a logical universe with axioms and no physical content
  Say instead: "Explain the Big Bang and the physical origin of our cosmos"
- Says: "What is the universe made of"
  Means: dark matter, atoms, energy
  May be taken as: describe a type-theoretic hierarchy of elements and sets
  Say instead: "What are the physical components of the observable universe"
- Says: "Create a universe for me"
  Means: a fictional world or setting
  May be taken as: generate a formal logical model or database schema
  Say instead: "Create a fictional world with its own history and rules for a story"
- Says: "Is this true in every universe"
  Means: could things be different elsewhere
  May be taken as: evaluate a statement across all possible models of a logical system
  Say instead: "Could this fact be different in another possible world or physical cosmos"

## Tips
- Say "physical universe" or "cosmos" when you mean space and astronomy
- Say "fictional universe" or "story world" when you mean a made-up setting
- Say "all possible cases" or "every instance" when you mean exhaustive coverage
- Say "complete dataset" or "full population" when you mean statistics not samples
- Avoid "universe" alone when you need a model to stay in plain English

## Often confused with
- world: smaller scope, one planet or society
- cosmos: more poetic, same physical meaning
- domain: technical, a specific area of knowledge
- multiverse: many universes, not one
- scope: technical, the range of variables or visibility
- ontology: technical, a formal catalog of what exists in a system