• Question: Dark energy - do you believe in its existence? And since there is no evident mass, but in theory there must be energy, could this energy be in the form of neutrinos?

    Asked by strangequark to Arttu on 14 Jun 2011.
    • Photo: Arttu Rajantie

      Arttu Rajantie answered on 14 Jun 2011:

      Yes, I think there probably is some dark energy. The alternative explanations are that general relativity is wrong (but it is difficult to modify the theory to fit the observations so dark energy is a simpler explanation) or our calculations are wrong (which is possible but it is hard to see how the error could be so large).

      Dark energy cannot be neutrinos or any other known particles because it has to have negative pressure to explain observations. The simplest explanation is that vacuum simply has non-zero energy density.

Comments

  • Photo: strangeness

    strangeness commented on :

    If a vacuum has non-zero energy density, does that mean that there is a fundamental property of the vacuum which causes space to expand? Is this property also true for places where there is mass, but overcome by the gravitational forces of the mass (although if this were true, wouldn’t the expansive “force” be very weak as gravity is a weaker force)? If this property is not true for regions containing mass, what is it about mass that distorts this property? (Sorry – that’s an awful lot of questions!)

  • Photo: strangequark

    strangequark commented on :

    Apparently, according to the astronomer who told me this, dark energy has a repulsive quality. She said that we can currently account for 25% of the mass needed for the expansion of the universe to not recollapse (including dark matter) and so the rest of this must be energy. Perhaps I interpreted this incorrectly, but this seemed to imply that the greater the distance between two galaxies, the stronger the repulsive force. Is that right, and if not, what qualities would this dark energy have?