  Many experiments have recently been proposed to test whether non-relativistic
gravitational interactions can generate entanglement. In this note, I consider
the extent to which these experiments can test if the graviton exists. Assuming
unitarity and Lorentz invariance of the $S$-matrix, I demonstrate that this
"Newtonian entanglement" requires the existence of massless bosons, universally
coupled to mass, in the Hilbert space of low-energy scattering states. These
bosons could be the usual spin-2 gravitons, but in principle there are other
possibilities like spin-0 scalar gravitons. I suggest a concept for a more
refined experiment to rule these out. The special role of $d=3+1$ spacetime
dimensions and the possibility that unitarity is violated by gravity are
highlighted.
