In order to adapt his theory to experimental results (redshift),
Einstein devised the so-called gravitational time dilation/contraction
which can be illustrated as follows. If a light source at the top of a
tower emits flashes at time intervals Ts and so acts as a clock, a
receiver on the ground will receive the flashes at time inervals 
Tr < Ts and will conclude that the tower clock ticks faster than an
identical clock on the ground. This will be confirmed if the former
clock is taken down and compared with the latter.

One of the implications amounts to a wizardry: with time, the number
of pulses received on the ground will become infinitely greater than
the number of pulses emitted by the tower clock. Relativists are not
allowed to ask any questions as to the origin of so many received
pulses. But they are wholeheartedly encouraged to advance deductions,
even not-all-there ones, which are consistent with gravitational time
dilation. One such deduction can be found here:

https://home.deds.nl/~dvdm/dirk/Physics/Fumbles/TheTheory.html

Pentcho Valev