# surface (exterior)

A part of a boundary that touches a thing and is where the thing is not the thing.

- Computed level: L4 (depth in the emergence graph, not abstraction)
- Status: review  ·  Domain: everyday  ·  Arena: physical

## Emergence
**Emerges from:** [boundary](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-boundary.limit), [touch](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-touch.together), [part](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-part.relation)

**Through:** When a boundary limit is touched by another thing, and a part of it stands in relation to that thing, exterior surface emerges at the place where the thing is not the thing.

**Novel properties:**
- facing aspect
- interaction perimeter
- non-internal interface

## Examples
- The event horizon of a black hole traps light but emits Hawking radiation at 10^-8 K for a solar-mass hole. *(physics)*
- A human epidermis regenerates every 4 weeks, forming a barrier that is not alive but made by living cells. *(biology)*
- The rusted hull of the RMS Titanic dissolves into the Atlantic floor, where iron-eating bacteria colonize the metal surface. *(engineering)*

## Used by
- [applying](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-applying.action) (L8)
- [beach](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-beach.geographic) (L15)
- [board](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-board.material) (L16)
- [color](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-color.visual) (L8)
- [display](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-display.visual) (L10)
- [face](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-face.body) (L16)
- [flat](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-flat.commonsurfacegeometry) (L15)
- [land](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-land.geography) (L10)
- [level](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-level.spatial) (L16)
- [marks](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-marks.visual) (L5)
- [page](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-page.sheet) (L16)
- [papering over the cracks](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-papering-over-the-cracks.upkeep) (L15)
- [pictures](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-pictures.visual) (L8)
- [press](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-press.force) (L5)
- [sand](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-sand.material) (L10)
- [screen](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-screen.visual) (L18)
- [street](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-street.path) (L13)
- [table](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-table.furniture) (L16)
- [visual](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-visual.perceptual) (L7)
- [windows](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-windows.opening) (L10)
- [write](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-write.communication) (L13)

---
*Canonical: https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-surface.exterior*  
*Structured data: https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-surface.exterior.json*  
*Every definition provably resolves to space, time, energy and pattern.*