Nature is subdivided in four kinds of stable elementary particles e, p, P and E and in two kinds of interactions; the electromagnetism and the gravitation.
No other particles and no other interactions are needed.
Also photons and gravitons are physically not needed. The so called wave-particle dualism is physically “unreal”. There exist localizable particles and continuous fields. The fields propagate with the constant velocity c.
The physics is to be described in finite ranges of Minkowski space and the positions and the velocities of particles can never observed exactly.
Einstein did not guess this kind of Nature.