@article {Davies469,
author = { and },
title = {Quantum theory and the equivalence principle},
volume = {381},
number = {1781},
pages = {469--478},
year = {1982},
doi = {10.1098/rspa.1982.0084},
publisher = {The Royal Society},
abstract = {The status of the gravitational principle of equivalence is obscure on the atomic scale, where quantum processes are relevant. On the assumption that a fundamental principle ought to apply to fundamental particles, we examine the principle of equivalence in a quantum context. We treat linearized gravitational perturbations as a massless, spin-two, gauge field coupled to itself and to matter, and argue that a consistent theory of this type, based on an action principle, is impossible unless the gravitational coupling is universal. The argument derives from a set of consistency conditions connecting successive orders of the perturbation expansion. We illustrate this consistency argument for scalar electrodynamics, and prove that the scalar particles must couple to gravity with the same strength as photons.},
issn = {0080-4630},
URL = {http://rspa.royalsocietypublishing.org/content/381/1781/469},
eprint = {http://rspa.royalsocietypublishing.org/content/381/1781/469.full.pdf},
journal = {Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences}
}