I attended a seminar today in which a new theory of dark energy was discussed. I'm not sure which forum to put this in, since it includes a lot from other fields, but since it is regarding dark energy, cosmology seems the best place. Here's a link to the paper http://arxiv.org/PS_cache/astro-ph/pdf/0703/0703364v2.pdf, and abstract The theory describes dark energy as fluctuations in the electromagnetic vacuum energy. The new physics that the authors invent involve describing the virtual photons to be in two states; a gravitationally active state, and a gravitationally inactive state (like spin up and spin down particles). Only photons in the gravitationally active state contribute to the cosmological constant. He then goes on to propose an experiment that can test this, using something called a Josephson junction (from superconductor physics). They have been given funding for this, and the apparatus is currently being built, and experiments should be done by next year. I'm not too sure how useful this will be, or even how correct or substantial the theory is, but it's a theory of dark energy that can be tested in the laboratory-- something which the other theories cannot! The good thing about the seminar was that the presenter did not state outrageous comments, or imply that this was groundbreaking physics: he was careful and even admitted it could easily be wrong, but I think I'll definitely be looking out for the results of the experiments!