Socratus, et al.... is this a science "fiction".... like aether of old?
Quintessence (physics) >From Wikipedia, the free encyclopedia For theories and defunct or classical concepts named after the synonym "Aether", see Aether (disambiguation)<http://en.wikipedia.org/wiki/Aether_%28disambiguation%29> . In physics <http://en.wikipedia.org/wiki/Physics>, *quintessence* is a hypothetical <http://en.wikipedia.org/wiki/Hypothesis> form of dark energy<http://en.wikipedia.org/wiki/Dark_energy>postulated as an explanation of observations of an accelerating universe <http://en.wikipedia.org/wiki/Accelerating_universe>. It has been proposed by some physicists to be a fifth fundamental force<http://en.wikipedia.org/wiki/Fifth_force>. Quintessence differs from the cosmological constant<http://en.wikipedia.org/wiki/Cosmological_constant>explanation of dark energy in that it is dynamic, changing over time, unlike the cosmological constant which always stays constant. It is suggested[*according to whom? <http://en.wikipedia.org/wiki/Wikipedia:Avoid_weasel_words>*] that quintessence can be either attractive or repulsive depending on the ratio of its kinetic and potential energy. Specifically, it is thought that quintessence became repulsive about ten billion years ago (the universe is approximately 13.8 billion years old).[1]<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#cite_note-1> Contents - 1 Scalar field<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#Scalar_field> - 2 Tracker behavior<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#Tracker_behavior> - 3 Specific models<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#Specific_models> - 4 Quintom scenario<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#Quintom_scenario> - 5 Terminology<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#Terminology> - 6 References<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#References> - 6.1 Further reading<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#Further_reading> - 7 External links<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#External_links> Scalar field Quintessence is a scalar field <http://en.wikipedia.org/wiki/Scalar_field>with an equation of state <http://en.wikipedia.org/wiki/Equation_of_State_%28Cosmology%29>where *w**q*, the ratio of pressure *p**q* and density [image: \rho]*q*, is given by the potential energy [image: V(Q)] and a kinetic term: [image: w_q=p_q/\rho_q=\frac{\frac{1}{2}\dot{Q}^2-V(Q)}{\frac{1}{2}\dot{Q}^2+V(Q)}] Hence, Quintessence is dynamic, and generally has a density and *w**q*parameter that varies with time. By contrast, a cosmological constant is static, with a fixed energy density and *w**q* = -1. Tracker behavior Many models of quintessence have a *tracker* behavior, which according to Paul Steinhardt <http://en.wikipedia.org/wiki/Paul_Steinhardt> *et al.* (1999) partly solves the cosmological constant problem<http://en.wikipedia.org/wiki/Cosmological_constant#Cosmological_constant_problem> .[2]<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#cite_note-Zlatev-2>In these models, the quintessence field has a density which closely tracks (but is less than) the radiation density until matter-radiation equality<http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang#Matter_domination>, which triggers quintessence to start having characteristics similar to dark energy <http://en.wikipedia.org/wiki/Dark_energy>, eventually dominating the universe. This naturally sets the low scale<http://en.wikipedia.org/wiki/Energy_scale>of the dark energy <http://en.wikipedia.org/wiki/Dark_energy>.[3]<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#cite_note-Steinhardt1999-3>When comparing the predicted expansion rate <http://en.wikipedia.org/wiki/Metric_expansion_of_space> of the universe as given by the tracker solutions with cosmological data, a main feature of tracker solutions is that one needs four parameters to properly describe the behavior of their equation of state<http://en.wikipedia.org/wiki/Equation_of_state_%28cosmology%29> ,[4]<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#cite_note-Linden2008-4> [5]<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#cite_note-Ferramacho2010-5>whereas it has been shown that at most a two-parameter model can optimally be constrained by mid-term future data (horizon 2015-2020).[6]<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#cite_note-LindererHuterer2005-6> Specific models Some special cases of quintessence are phantom energy<http://en.wikipedia.org/wiki/Phantom_energy>, in which *w**q* < -1,[7]<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#cite_note-Caldwell2002-7>and k-essence<http://en.wikipedia.org/w/index.php?title=K-essence&action=edit&redlink=1>(short for kinetic quintessence<http://en.wikipedia.org/w/index.php?title=Kinetic_quintessence&action=edit&redlink=1>), which has a non-standard form of kinetic energy<http://en.wikipedia.org/wiki/Kinetic_energy>. If this type of energy were to exist, it would cause a big rip<http://en.wikipedia.org/wiki/Big_rip>in the universe due to the growing energy density of dark energy which would cause the expansion of the universe to increase at a faster-than-exponential rate. Quintom scenario In 2004, when scientists fit the evolution of dark energy with the cosmological data, they found that the equation of state had possibly crossed the cosmological constant boundary<http://en.wikipedia.org/w/index.php?title=Cosmological_constant_boundary&action=edit&redlink=1>(w=-1) from above to below. A proven no-go theorem <http://en.wikipedia.org/wiki/No-go_theorem>[*which? <http://en.wikipedia.org/wiki/Wikipedia:Avoid_weasel_words>*] indicates this situation, called the Quintom scenario<http://en.wikipedia.org/wiki/Quintom_scenario>, requires at least two degrees of freedom for dark energy models.[8]<http://en.wikipedia.org/wiki/Quintessence_%28physics%29#cite_note-Hu2005-8> Terminology The name comes from the classical elements<http://en.wikipedia.org/wiki/Classical_element#Classical_elements_in_Greece>in ancient Greece. The aether <http://en.wikipedia.org/wiki/Aether_%28classical_element%29>, a pure "fifth element" (*quinta essentia* in Latin), was thought to fill the Universe beyond Earth. Similarly, modern quintessence would be the fifth known contribution to the overall mass-energy content of the Universe. (The other four in the modern interpretation, different from the ancient ideas, are: baryonic matter <http://en.wikipedia.org/wiki/Baryon>; radiation - photons and the highly relativistic neutrinos<http://en.wikipedia.org/wiki/Neutrinos>, which may be considered hot dark matter<http://en.wikipedia.org/wiki/Hot_dark_matter>; cold dark matter <http://en.wikipedia.org/wiki/Cold_dark_matter>; and the term due to spatial curvature - loosely, gravitational<http://en.wikipedia.org/wiki/Gravitation> self-energy <http://en.wikipedia.org/wiki/Self-energy>.) -- You received this message because you are subscribed to the Google Groups "Epistemology" group. To unsubscribe from this group and stop receiving emails from it, send an email to epistemology+unsubscr...@googlegroups.com. To post to this group, send email to epistemology@googlegroups.com. Visit this group at http://groups.google.com/group/epistemology. For more options, visit https://groups.google.com/groups/opt_out.
