  In the standard model of particle physics, photons are mass-less particles
with a particular dispersion relation. Tests of this claim at different scales
are both interesting and important. Experiments in territory labs and several
exterritorial tests have put some upper limits on photon mass, e.g. torsion
balance experiment in the lab shows that photon mass should be smaller than
$1.2\times 10^{-51}\rm g$. In this work, this claim is tested at a cosmological
scale by looking at strong gravitational lensing data available and an upper
limit of $8.71\times 10^{-39}$g on photon mass was given. Observations of
energy-dependent gravitational lensing with not yet available higher accuracy
astrometry instruments may constrain photon mass better.

Cosmology and Nongalactic Astrophysics