We know that radiation energy density scales as $a^{-4}$ with EoS parameter ($w=\frac{1}{3}$), matter as $a^{-3}$ with ($w=0$), curvature as $a^{-2}$ with ($w=-\frac{1}{3}$).

Then which kind of matter density scales as $a^{-1}$ with $w=-\frac{2}{3}$? As for these kind of matter $w<-\frac{1}{3}$, these would cause accelerated expansion of the universe.

Are these kinds of matter known and studied in cosmology?

  • $\begingroup$ If I was Sam Bankman-Fried, I would hype it as dark energy 2.0 (anything with $w<-\frac{1}{3}$ could drive the acceleration of the universe, including dark energy 1.0 with $w=-1$) and solicit investment in this novel clean energy. And even better, SBF would have bundled this dark energy 2.0 with the Fusion breakthrough of Lawrence Livermore National Laboratory, and parked the giddy investors' money in the wormhole created by Google's Santa Barbara quantum computer lab. $\endgroup$
    – MadMax
    Dec 15, 2022 at 17:04


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