Gravitational redshift and the vacuum index of refraction

Abstract

A physical process of the gravitational redshift was described in an earlier paper (Wilhelm and Dwivedi, New Astron. 31:8, 2014). This process did not require any information for the emitting atom neither on the local gravitational potential $U$ nor on the speed of light $c$ . Although it could be shown that the correct energy shift of the emitted photon resulted from energy and momentum conservation principles and the speed of light at the emission site, it was not obvious how this speed is controlled by the gravitational potential. The aim of this paper is to describe a physical process that can accomplish this control. We determine the local speed of light $c$ by deducing a gravitational index of refraction $n_{\mathrm{G}}$ as a function of the potential $U$ assuming a specific aether model, in which photons propagate as solitons. Even though an atom cannot locally sense the gravitational potential $U$ (cf. Muller et al., Nature 467:E2, 2010) the gravitational redshift will nevertheless be determined by $U$ (cf. Wolf et al., Nature 467:E1, 2010)—mediated by the local speed of light $c$ .