Massless GR is sometimes called "pure gravity", and is something people are still interested in (or were, last time I was paying attention) [1]. Kind of remark

Massless GR is sometimes called "pure gravity", and is something people are still interested in (or were, last time I was paying attention) [1]. Kind of remarkable that even the base-case has so many open issues. I should re-read that Torretti book, I remember liking his style but that some of the math was over my head at the time. [1] http://arxiv.org/abs/0706.3359 http://arxiv.org/abs/0706.3359