Troubles With Gravitational Frequency Shift Derived From Energy Conservation

Abstract

In physics, thought experiments are impressive heuristic tools. They are valuable instruments to help scientists find new results and to teach students the known ones. However, as we shall show, they should always be received with prudence, even when they are a shortcut to 'prove' well-established results. Here, we show that the most widely known thought experiments devised to derive the gravitational frequency shift from energy conservation are, in fact, problematic. Unfortunately, even some criticism of them found in the literature seems to share a similar fate. When properly set and correctly read, those thought experiments reveal that the existence of the gravitational frequency shift is, in fact, at odds with energy conservation. However, in light of the well-known experimental proofs of the gravitational redshift, our findings cannot be considered a confutation of the phenomenon. Nonetheless, our results may be of some epistemological interest and could serve as a warning sign on how thought experiments should be received and trusted.