From The Economist:
Three decades of effort have been expended on string theory, which includes gravity but at the expense of having the universe inelegantly sprout hidden dimensions. Other potential avenues, such as loop quantum gravity, are also proving untidy. That a theory of everything might emerge from geometry would be neat, but it is a long shot.
Nevertheless, that is what Garrett Lisi is proposing. The geometry he has been studying is that of a structure known to mathematicians as E8, which was first recognised in 1887 by Sophus Lie, a Norwegian mathematician. E8 is a monster. It has 248 dimensions and its structure took 120 years to solve. It was finally tamed earlier this year, when a group of mathematicians managed to construct a map that describes it completely.
Dr Lisi had been tinkering with some smaller geometries. Soon after reading about this map, however, he realised that the structure of E8 could be used to describe fully the laws of physics. He placed a particle (including different versions of the same entities, and using particles that describe matter and those that describe forces) on most of the 248 points of E8. Using computer simulations to manipulate the structure, he was able mathematically to generate interactions that correspond to what is seen in reality.
More here.