Light from a lensed object takes longer to reach us than light from an unlensed object at the same distance primarily due to the Shapiro delay effect. This phenomenon occurs because light slows down in lower gravitational potentials, akin to traveling through a medium with a refractive index greater than 1. The time delay is influenced by the gravitational field and the potential along the light path, rather than just the curvature of the path itself. For further reading, refer to the lectures on gravitational lensing by Narayan and Bartelmann.
PREREQUISITESAstronomers, astrophysicists, and students studying gravitational lensing and the effects of gravity on light propagation will benefit from this discussion.
scupydog said:Hi. Does the light from a lensed object take longer to reach us, than the light from an unlensed object at the same distance.
I mean because the light from a lensed object has a curved path.
Thx. Dave...
Chronos said:Correct. For discussion see
http://arxiv.org/abs/astro-ph/9606001
Lectures on Gravitational Lensing
authors: Narayan, Bartelmann
Jonathan Scott said:Yes, it takes longer to reach us but this is normally mainly because of the Shapiro delay effect rather than simply the curved path. Basically, light slows down slightly in a lower gravitational potential, closer to a massive object or system, as if it were in a medium with a refractive index slightly greater than 1. The amount of deflection relates to the gravitational field (how rapidly that potential changes with sideways displacement along the light path) but the amount of time delay mainly relates to the potential along the path.