The discussion centers on the bidirectional nature of light speed in the context of an expanding universe, specifically regarding the NASA Voyager probes. Participants confirm that the average nonlocal speed of light remains constant when traveling to and from the Sun, despite gravitational influences. They emphasize the importance of simultaneity conventions in measuring coordinate speed, which can yield arbitrary results based on chosen reference frames. Key invariants, such as round-trip time and frequency shifts due to the Doppler effect, are highlighted as unaffected by these conventions.
PREREQUISITESAstronomers, physicists, and anyone interested in the implications of relativity on light propagation and cosmic measurements will benefit from this discussion.
Tracer said:f gravitational fields are -conservative
PeterDonis said:They aren't in an expanding universe. More precisely, in an expanding universe, the concept of "gravitational field" is not well-defined.