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The Question

(Submitted September 15, 2012)

What is the driving force behind dark energy? Is it the same thing as vacuum energy?

The Answer

We don't know what causes dark energy.

Dark energy and vacuum energy may be related,but they don't appear to be the same thing. Vacuum energy is a manifestation of quantum mechanics and the Heisenberg uncertainty relation that delta-E x delta-t is greater than or equally to Planck's constant divided by 2. Basically everything has a small residual energy - that is delta-E can never be total zero. There can be other contributions as well.

Dark energy is a possible explanation of the observed behavior of the Universe at very large scales. Conceptually it appears to permeate all of space and look like a very slightly repulsive gravitational interaction. A calculation of the vacuum energy gives something too large to be dark energy, but there must be more to the story. We just don't know what that story is.

Here is a good discussion of the issues:
http://blogs.discovermagazine.com/cosmicvariance/2011/10/04/

Jay and Jeff
for Ask an Astrophysicist

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