2 2 4 D O C U M E N T 9 4 J U L Y 1 9 2 0
same place in time in the same state of motion. Time t is conventional; but in the
static case, time t is universally given (with the exception of an additive correction),
if it is given at one location. For in the static case, time t has physical meaning to
the extent that it is chosen so as to make static or stationary processes appear re-
spectively as static or stationary. If I allow, e.g., monochromatic light to travel from
the Sun to the Earth, then the time interval t for generating 100 oscillations is
equal to the time interval t for receiving the 100 oscillations on Earth. With an-
other time choice, the process of light propagation between Sun and Earth would
not appear
stationary.[3]
For resting standard clocks that are set up at two locations, one has the equations
.
We now want to assume further that location (1) is the Sun’s surface; location (2),
however, is only so far away from the Sun that the special theory of relativity still
applies precisely enough. Then (g44)2 = 1 or s2 = t2 is true. In the conventional
unit of time ( t)2 = 1, the standard clock hence strikes exactly once ( s2 = t2 = 1).
On the Sun, however, for the same conventional time unit ( t)1 = 1, which accord-
ing to the foregoing case of the static field has direct physical meaning,
.
Hence, in the conventional unit of time, the clock makes less than one stroke (since
g44 1).
Alternatively, one can also reason like this. If the clock strikes once on the Sun,
s = 1, then the elapsed conventional time (which preserves the system’s static
character)
.
The equation you cited[4]
makes no sense to me either.
When you write back to me, please remain consistent in having the ’s be
lengths of a clock’s period measured by a special standard clock.
Best regards, yours,
A. Einstein.
s
1
g44
1
t
1
=
s
2
g44
2
t
2
=
s2 g44
1
=
g44 t1 1=
t1
1
g44
----------- 1 =
dt
sun
dt
g44
----------- =