Quintessence (physics)

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For other uses, see Quintessence (disambiguation).

In physics, quintessence is a hypothetical form of dark energy postulated as an explanation of observations of an accelerating universe.

[edit] Scalar field

Quintessence is a scalar field which has an equation of state (relating its pressure pq and density ρq) of pq = wρq, where w is less than -1/3. Quintessence is dynamic, and generally has a density and equation of state that varies through time and space. By contrast, a cosmological constant is static, with a fixed energy density and w = −1.

[edit] Tracker behavior

Many models of quintessence have a tracker behavior, which partly solves the cosmological constant problem. In these models, the quintessence field has a density which closely tracks (but is less than) the radiation density until matter-radiation equality, which triggers quintessence to start having characteristics similar to dark energy, eventually dominating the universe. This naturally sets the low scale of the dark energy.

[edit] Phantom energy

Some special cases of quintessence are phantom energy, in which w < −1, and k-essence (short for kinetic quintessence) which has a non-standard form of kinetic energy.

[edit] Terminology

The name comes from the Classical elements of the ancient Greeks, where a pure "fifth element," the aether, was thought to fill the Universe beyond Earth.

[edit] External links