What does it mean to say that "6 tons of dark energy would be found within the radius of Pluto's orbit"?

  • Does it mean that the dark energy is orbiting the solar system?
  • Or does it mean a flow of dark energy through a sphere?
  • Or does it refers to an energy in a particular system of inertia in the solar system?

Or what?

Again on a mass–energy equivalence basis, the density of dark energy (6.91 × 10−27 kg/m3) is very low: in the solar system, it is estimated only 6 tons of dark energy would be found within the radius of Pluto's orbit. However, it comes to dominate the mass–energy of the universe because it is uniform across space. Wikipedia/Dark energy

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    $\begingroup$ They used $E=mc^2$ to convert energy density into mass density, or so it seems. I could not guess why they did it since giving a mass of dark energy is both confusing and misleading. Best to ignore the 6 tons thing $\endgroup$
    – Jim
    Nov 19, 2014 at 16:49
  • $\begingroup$ What do you mean by "system of inertia?" $\endgroup$
    – user4552
    Nov 19, 2014 at 16:54
  • $\begingroup$ Ben Crowell: some geometrical frame with no movement relative the sun. $\endgroup$
    – Lehs
    Nov 19, 2014 at 17:01

1 Answer 1


We don't really know what dark energy is, but the default description is that it's not really dynamical. It can't flow or orbit. It's just a fixed built-in energy that is possessed by every cubic centimeter of space.

On a more technical level, the simplest way to accomodate dark energy in the Einstein field equations is by adding a cosmological constant term. Naive attempts to make it variable rather than constant cause the stress-energy tensor to have a nonvanishing divergence, which makes GR not self-consistent.


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