Quintessence
Cosmology
Quintessence is a hypothetical form of energy postulated to exist as a possible explanation of observations of an accelerating universe. Quintessence is a type of vacuum energy defined as having an equation of state (relating its pressure pq and density q) of pq = wq. If , the quintessence acts as a repulsive field, pushing space apart, and it is this property which makes quintessence a possible candidate for dark energy. In general, the parameter w can vary with cosmological time, although some theorists refer to quintessence with a time-variable w as kinessence to distinquish it from more stolid forms of energy that have an equation of state in which w remains constant. Also, the term quintessence is generally not used to describe any hypothesised energy that has an equation of state in which . A non-zero cosmological constant can be seen as a special case where and does not vary in time. Another special case is phantom energy, in which .
External links
\n* Dark Energy dominates the Universe (outreach poster from University of Bonn)
Elements
Among the classical elements, quintessence (meaning "fifth element", along with earth,
air,
fire, and
water) was another term for
aether.
Alchemy
In alchemy, quintessence is the purest form of a particular
element (as one would conceive them today). This is seen in the
Hamlet soliloquy: "The beauty of the world, the paragon of animals and yet to me what is this quintessence of dust?"
