Spacetime is a mathematical model that Einstein used to <i>derive</i> his field equations. Philosophically speaking, we are reminded to not confuse the model with reality. Even Einstein reminded us of that, even in regard to curved spacetime.<p>WRT to particles, we now model them as excitations of a quantum field. Quantum Field Theory, or QFT, is our most recent quantum theory and is the theory the Standard Model is based on. As such, it's enjoyed phenomenal success.