Yet, Big Bang cosmology is vulnerable. It is based on GR being accurate over an enormous range of scales in time and space. The entire orbit of Mercury rotates because of the curved geometry of space near the sun. The amount of 'perihelion shift' each century was well known at the time Einstein provided a complete explanation for it in 1915. Light at every frequency can be bent in exactly the same way by gravity.
Clocks run slower in strong gravitational fields.
This was confirmed by Robert Pound and George Rebka at Harvard University in 1959, and by Robert Vessot in the 1960's and 70's using high-precession hydrogen maser clocks flown on jet planes and on satellites. Gravitational mass and inertial mass are identical. Black holes exist. Although these objects have been suspected to exist since they were first introduced to astronomers in the early 1970's, it is only in 1992 that a critical acceptance threshold was crossed in the astronomical community. It was then that Hubble Space Telescope observations revealed monstrous, billion-sun black holes in the cores of nearby galaxies such as Messier 87, Messier 33 and NGC 4261.