This week I started looking into models which try to explain the observed accelerated expansion of the Universe with modifications of gravity instead of introducing a dark energy component. It turns out that it is not too easy to solve for the dynamics of Universe in these models, but the paper shows nicely the possibilities. We are currently investigating what bounds observations can put on this models.

Since most theorists genuinely dislike the presence of a fine tuned cosmological constant in the Universe, they try to come up with alternative explanations. Recently a paper was posted to the archive by Kolb and collaborators, which tries to explain the apparently accelerated expansion of the Universe with primordial large scales inhomogeneities. This paper is very controversial and has sparked already in a short time 5 follow up papers, where 4 of them try to refute the idea. We will have a discussion about this next week and I hope the sparks will fly. I quite like this. I think this is how science is actually at its best. Suggestion of ideas and "violent" discussion about them. I will let you know about the outcome of the discussion -- if there is one.