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The density of dark matter in an expanding universe decreases more quickly than dark energy, and eventually the dark energy dominates. Specifically, when the volume of the universe doubles, the density of dark matter is halved, but the density of dark energy is nearly unchanged (it is exactly constant in the case of a cosmological constant).
A positive energy density leads to deceleration of the expansion, ¨ <, and a positive pressure further decelerates expansion. On the other hand, sufficiently negative pressure with p < − ρ c 2 / 3 {\displaystyle p<-\rho c^{2}/3} leads to accelerated expansion, and the cosmological constant also accelerates expansion.
A cosmological constant has negative pressure, =, which contributes to the stress–energy tensor that, according to the general theory of relativity, causes accelerating expansion. The fraction of the total energy density of our (flat or almost flat) universe that is dark energy, , is estimated to be 0.669 ± 0.038 based on the 2018 Dark ...
Dark energy is one of the greatest mysteries in science today. One of the simplest explanations is that it is a “cosmological constant” – a result of the energy of empty space itself – an ...
“Dark energy is a misidentification of variations in the kinetic energy of expansion, which is not uniform in a Universe as lumpy as the one we actually live in.
The findings announced on Tuesday are part of a years-long study of the history of the cosmos focusing upon dark energy, an invisible and enigmatic force that is accelerating the ongoing expansion ...
The universe's expansion passed an inflection point about five or six billion years ago when the universe entered the modern "dark-energy-dominated era" where the universe's expansion is now accelerating rather than decelerating. The present-day universe is quite well understood, but beyond about 100 billion years of cosmic time (about 86 ...
Different theories of dark energy suggest different values of w, with w < − 1 / 3 for cosmic acceleration (this leads to a positive value of ä in the acceleration equation above). The simplest explanation for dark energy is that it is a cosmological constant or vacuum energy; in this case w = −1.