Elementary particle and Gravitational fields Does an elementary particle that doesn't interact with gravity, just like how dark matter doesn't interact with EM radiation, exist? If so could this particle go in and out of Black holes without being affected?
 A: Einstein's general theory of relativity gives a different perspective on gravity: it is not a force, but a property of spacetime.
Being more precise: a freely-falling particle (not acted upon by any force other than gravity) follows a geodesic of spacetime - the straigthest spacetime path available compatible with the initial conditions of said particle.
In that sense, it is not possible to decouple a particle from the gravitational effects upon it. The particle lives on spacetime and must follow its geometry and this is what we observe as gravity according to Einstein's GR.
On the other hand: Einstein's Field Equations reads
$$R_{\mu\nu}-\dfrac{1}{2}g_{\mu\nu}R=\kappa T_{\mu\nu}$$
where the RHS is the energy-momentum tensor and the LHS is Einstein's tensor. This equations determines locally the spacetime metric tensor and hence the spacetime geometry and hence the gravitational effects one would observe.
It turns out that it tells that energy acts as a source of gravity. Hence: inasmuch as gravity affects any particle because it is a property of spacetime from which the particle cannot be decoupled, every particle backreacts on spacetime affecting its geometry because every particle has energy and hence contributes to $T_{\mu\nu}$ on the right hand side of Einstein's equations.
