# equivalence reloaded

16 May 2018Equivalence was introduced because gravity as a geometrical phenomenon would not distinguish between matter of different type or mass concerning the motion in a gravitational field. But if one looks at the kinetic part of the Lagrange density of e.g. a scalar particle \(\varphi\), \(\mathcal{L} = g^{\mu\nu}\nabla_\mu\varphi\nabla_\nu\varphi\). Wouldn’t this look like the interaction of the scalar field with the graviton, and wouldn’t it be natural to include a coupling strength, i.e. a mass?