http://www.astronomytoday.com/cosmology/quintessence.html/ further reading....
On Friday, December 27, 2013 12:26:24 PM UTC-5, nominal9 wrote: > > 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. 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