Title: "Pushing the Void to the limits: a good fit to CMB, BAO, SN and HST."

The expansion of the universe appears to accelerate. This leads us to the inclusion of a cosmological constant or more elaborate models of Dark Energy. However, a simple toy model putting the observer in the centre of a spherically symmetric void, leads to the same observational effects as a cosmological constant. If such a simple model explains the data, while violating the copernican principle but only invoking Dark Matter and General Relativity, are we sure that we are on the right track then? After a broad introduction to the observational evidence for Dark Energy, I will one by one show how a large local void can fit these observations exactly without a cosmological constant. Then I will go through the signatures that could rule out this non-copernican model, pointing out what work needs to be done to establish LCDM as a valid paradigm.