An Exceptionally Simple Theory of Everything

"An Exceptionally Simple Theory of Everything"^[1] is a physics preprint proposing a basis for a unified field theory, often referred to as "E₈ Theory",^[2] which attempts to describe all known fundamental interactions in physics and to stand as a possible theory of everything. The paper was posted to the physics arXiv by Antony Garrett Lisi on November 6, 2007, and was not submitted to a peer-reviewed scientific journal.^[3] The title is a pun on the algebra used, the Lie algebra of the largest "simple", "exceptional" Lie group, E₈. The paper's goal is to describe how the combined structure and dynamics of all gravitational and Standard Model particle fields are part of the E₈ Lie algebra.^[2]

The theory is presented as an extension of the grand unified theory program, incorporating gravity and fermions. The theory received a flurry of media coverage, but was also met with widespread skepticism.^[4] Scientific American reported in March 2008 that the theory was being "largely but not entirely ignored" by the mainstream physics community, with a few physicists picking up the work to develop it further.^[5] In July 2009, Jacques Distler and Skip Garibaldi published a critical paper in Communications in Mathematical Physics called "There is no 'Theory of Everything' inside E₈",^[6] arguing that Lisi's theory, and a large class of related models, cannot work. Distler and Garibaldi offer a direct proof that it is impossible to embed all three generations of fermions in E₈, or to obtain even one generation of the Standard Model without the presence of additional particles that do not exist in the physical world.