As far as I understand it, you can decide which part of the dynamics you put into the spacetime, and which part into the fields. So a spin-2 field on a flat spa

As far as I understand it, you can decide which part of the dynamics you put into the spacetime, and which part into the fields. So a spin-2 field on a flat spacetime is equivalent to general relativity. (And you can't tell the difference because you can't detect individual gravitons, among other reasons.) A smiliar cool idea that I encountered in a string theory course, is when you have tachyons. They seem pretty bad because you can gain energy by creating more tachyons, and your spacetime would decay. But what it really means is that you have chosen a "wrong" spacetime, and you can transform the tachyons away by choosing a different background. (Handwaving here since I'm just an experimentalist ;-))