[naasking]

> Essentially, when we state that H2O has less mass than H+H+O, what we actually mean is that H2O bends spacetime a little bit less than the three atoms individually that made it up. There's no accepted variant of QM or the Standard Model that explains this.

I'm not sure this is correct. It bends spacetime less simply because it's in a lower energy state. It's correct to say that the Standard Model doesn't explain spacetime curvature, but the curvature in GR is implied by the energy which is explained.