What is "geon"

n. 1 (context physics English) A hypothetical electromagnetic or gravitational wave held together in a confined region by the gravitational attraction of its own field energy. 2 (context psychology English) Any of a group of geometric forms capable of being recognised as a component of a real object

Geon may refer to:

• Geon (geology), a time interval
• Geon (Korean name), a Korean masculine given name
• Geon (physics), a hypothetical gravitational wave packet
• Geon (psychology), a geometrical primitive out of which everyday objects can be represented
• Geon, short for geonim, rabbis in the medieval era
• Geon, a character from the King of the Monsters series of video games
• Geon: Emotions, a video game for Xbox 360's Xbox Live Arcade service
• Geon (video game), for PlayStation 3's PlayStation Network and Nintendo Wii

In theoretical general relativity, a geon is an electromagnetic or gravitational wave which is held together in a confined region by the gravitational attraction of its own field energy. They were first investigated theoretically in 1955 by J. A. Wheeler, who coined the term as a contraction of "gravitational electromagnetic entity".

Since general relativity is a classical field theory, Wheeler's concept of a geon does not treat them as quantum-mechanical entities, and this generally remains true today. Nonetheless, Wheeler speculated that there might be a relationship between geons and elementary particles. This idea continues to attract some attention among physicists, but in the absence of a viable theory of quantum gravity, the accuracy of this speculative idea cannot be tested.

Wheeler did not present explicit geon solutions to the vacuum Einstein field equation, a gap which was partially filled by Brill and Hartle in 1964 by the Brill-Hartle geon. In 1997, Anderson and Brill gave a rigorous proof that geon solutions of the vacuum Einstein equation exist, though they are not given in a simple closed form.

A major outstanding question regarding geons is whether they are stable, or must decay over time as the energy of the wave gradually "leaks" away. This question has not yet been definitively answered, but the consensus seems to be that they probably cannot be stable. This would lay to rest Wheeler's initial hope that a geon might serve as a classical model for stable elementary particles. However, this would not rule out the possibility that geons are stabilized by quantum effects.

Geons are the simple 2D or 3D forms such as cylinders, bricks, wedges, cones, circles and rectangles corresponding to the simple parts of an object in Biederman's Recognition-by-components theory. The theory proposes that the visual input is matched against structural representations of objects in the brain. These structural representations consist of geons and their relations (e.g., an ice cream cone could be broken down into a sphere located above a cone). Only a modest number of geons (< 40) are assumed. When combined in different relations to each other (e.g., on-top-of, larger-than, end-to-end, end-to-middle) and coarse metric variation such as aspect ratio and 2D orientation, billions of possible 2- and 3-geon objects can be generated. Two classes of shape-based visual identification that are not done through geon representations, are those involved in: a) distinguishing between similar faces, and b) classifications that don’t have definite boundaries, such as that of bushes or a crumpled garment. Typically, such identifications are not viewpoint-invariant.

The term geon (for geological eon) refers to large, geologic units of time. Geologists traditionally subdivide Earth history into a hierarchy of named intervals: eons, eras, periods, etc. (e.g., the Jurassic Period of the Mesozoic Era). Historians subdivide the history of human activity into intervals that are comparatively much shorter. In both geological and historical scales, the divisions of equal rank are characteristically of unequal duration, and the identification of a particular interval is primarily based on its fossil, artifact, or cultural content (e.g., Carboniferous, Neolithic, Dark Ages, Ming Dynasty). Both scales are calibrated against numerical ages obtained separately.

An alternative way of referring to the past is to use a scale with intervals of equal duration. We speak of a given decade, century, or millennium. For the enormously long geologic time frame, it is advantageous to use corresponding large, equal time intervals encompassing the events and processes that have shaped our planet. The development of mountain ranges, ocean basins, and continents takes tens to hundreds of millions of years, and large time units thus are convenient for discussing long-term trends. Astronomers use light years and parsecs to deal with huge distances, rather than kilometres. Geologists have geons to refer to large specified time intervals of Earth history. The geon scale is also applicable to other planets with different histories, and to the universe itself.

Two usages of geon have been introduced in geology:

1. A geon is a unit “...taken to represent either the span of the average geologic period, or the thickness of the average stratigraphic equivalent, a matter of 60,000,000 years, and 50,000 feet [~15 km] of clastic depositions” (Woodward, 1929). Utilizing the currently accepted value of 542 Ma, million years ago) for the beginning of the Cambrian Period, and using 11 geologic periods in the Phanerozoic Eon, an updated value for Woodward’s geon would be about 49.4 million years. Usage in this sense is not current.

1. A geon is a specified 100-million-year interval of geologic time, counted backward from the present. The geon scale can be likened to a ladder, each interval between rungs representing 100 million years. Geons are named for the leftmost part of the number representing age. For example, the Earth formed about 4550 million years ago, an event that is assigned to Geon 45 (interval below rung 45). Rocks formed at 1851 Ma or 1800 Ma both belong to Geon 18. The extinction of the dinosaurs at the end of the Cretaceous Period (065 Ma) belongs to Geon 0. (Hofmann, 1990).

Geon is a multiplayer-oriented action arcade video game developed by independent software developer Strawdog Studios. The initial version of the game was originally released as "Geon: Emotions" for the Xbox 360's XBLA service in September 2007.

The title has since been updated, improved and was released on 25 September 2008 via the PlayStation 3's PlayStation Store. The Wii version of the game was released on October 27, 2009.