2011/03/16 by Sun Hong Rhie, Rhie, Sun Hong
Earth and Planetary Sciences · Physics and Astronomy · #Cosmology and Gravitation Theories #FOS: Physical sciences #General Physics (physics.gen-ph) #Geophysics and Gravity Measurements #Pulsars and Gravitational Waves Research #physics.gen-ph
paper · pdf · doi:10.48550/arxiv.1103.3144
6 p., 1 fig
arxiv created 2011/03/16 · openalex publication_date 2011/03/16 · arxiv updated 2011/03/17 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The current standard time delay formula (CSTD) in gravitational lensing and its claimed relation to the lens equation through Fermat's principle (least time principle) have been puzzling to the author for some time. We find that the so-called geometric path difference term of the CSTD is an error, and it causes a double counting of the correct time delay. We examined the deflection angle and the time delay of a photon trajectory in the Schwarzschild metric that allows exact perturbative calculations in the gravitational parameter GM in two coordinate systems -- the standard Schwarzschild coordinate system and the isotropic Schwarzschild coordinate system. We identify a coordinate dependent term in the time delay which becomes irrelevant for the arrival time difference of two images. It deems necessary to sort out unambiguously what is what we measure. We calculate the second order corrections for the deflection angle and time delay. The CSTD does generate correct lens equations including multiple scattering lens equations under the variations and may be best understood as a generating function. It is presently unclear what the significance is. We call to reanalyze the existing strong lensing data with time delays.