Gravitational Lensing, Redshift & Time Dilation: Structures & Vocabulary

Curved spacetime changes the paths of light and the rates of clocks. Gravitational lensing bends light around mass, gravitational redshift reduces photon frequency as radiation climbs out of a gravitational potential, and gravitational time dilation causes clocks deeper in gravity to accumulate less proper time than clocks farther away.

Photons follow null geodesics through curved spacetime. Different trajectories and potentials create path delays and magnification. Clocks at different gravitational potentials trace worldlines with different proper times, and photon frequencies measured by those clocks differ accordingly.

Solar-eclipse and radio observations confirm light deflection, galaxy clusters produce dramatic gravitational arcs, atomic clocks show gravitational time shifts over small height differences, and compact-star spectra can exhibit gravitational redshift.

Strong lensing can create multiple images and arcs; weak lensing produces subtle coherent shape changes; microlensing changes unresolved brightness. Gravitational redshift and time dilation compare clocks or photon frequencies at different gravitational potentials.