Lisi posted this yesterday over at Physics Forums; I reproduce here:
Hello PF folk.
If you believe the Dirac equation in curved spacetime, and you believe Spin(10) grand unification, then a Spin(3,11) GraviGUT, acting on one generation of fermions as a 64 spinor, seems… inevitable.
Also, it’s pretty.
And it’s up to you whether or not to take seriously or not the observation that this whole structure fits in E8. Personally, I take it seriously. Slides are up for a talk I gave at Yale:
I am not certain whether it addresses Distler’s previous objections (as I am not certain whether the issue was even settled at that time– see here and here, which goes as far as I could follow. More (older) personal opinions can be found here, here and here in reverse chronological order).
Edit: I forgot to add. I do find the theory beautiful and interesting. I hope it can be properly tested.
Edit: Here are further links that are relevant to this post.
There is no “Theory of Everything” inside E8 by Jacques Distler and Skip Garibaldi.
Here is Distler’s blog entry on his paper.
There was a discussion of Distler and Garibaldi’s paper at Physics Forums some time ago.
There was also a discussion at n-Category Café some time ago.