Is EVERYTHING affected by gravity?

[Runner 1]

Generalizing somewhat on my other post, I have to wonder -- if everything observable has an energy associated with it, then it is a form of mass as well, right? And all mass is affected (and causes) gravity, right? (And I don't mean rest mass -- I mean total mass.)

Am I missing something stupid/obvious here?

 

[mathman]

The answer is yes. In the case of photons this was confirmed by the 1919 Eddington experiment.

 

[Matterwave]

If one views gravity as a curvature in space-time then obviously everything which lives in space-time (i.e. everything) is affected by gravity. If this were not true, there would be a violation of the equivalence principle.