The origin of the current  accelerated expansion of the Universe remains one of the major unsolved  mysteries in physics today. While this could be a sign of the mysterious  “Dark Energy”, this puzzling observation might also be evidence for the  inadequacy of Einstein’s theory of General Relativity (GR) to describe  the law of gravity on very large cosmological scales. These  considerations would have strong implications on our understanding of  fundamental physics, warranting dedicated studies such as the one  undertaken recently by researchers at MPA and MPE. In this work, the  authors created mock universes with non-GR theories of gravity to test  the validity of current observational methods to determine the rate at  which structures grow in the Universe. This allowed them to place bounds  on how much the current data allows the Universe to depart from  Einstein’s prediction. Reassuringly, current observational methods do  not show evidence for a biased performance when tested on mock universes  with modified gravity.

Figure 1:Schematic representation of the DGP brane model. Matter and radiation are confined to the  four-dimensional brane, but the gravitational interaction is free to  propagate out into the additional fifth dimension.

 See: http://www.mpa-garching.mpg.de/404826/hl201702