Rummaging for a Final Theory: Can a 1960s Approach Unify Gravity with the Rest of Physics?: Scientific American: "Not everyone shares this optimism. Skip Garibaldi, a mathematician at Emory University, says that E8-inspired nostalgia is misguided. Working with physicist Jacques Distler of the University of Texas at Austin, Garibaldi has shown that Lisi’s theory predicts the existence of unwanted particles, whose interactions are the mirror image of regular fermions. Such particles would most likely have already exerted a noticeable effect on known particles, Garibaldi argues. “There is no way to shove gravity inside E8 without also predicting something that has nearly been ruled out by experiment,” he says.
Lisi, who posted the latest version of his theory on the Internet in June and presented it at the meeting, concedes that mirror fermions are an issue but adds that E8 theory is a work in progress and that mirror fermions could have evaded notice if they are heavier than commonly thought. They could even show up in the Large Hadron Collider, he says."