D O C U M E N T 1 3 2 S E P T E M B E R 1 9 2 0 2 5 9

I asked Grebe to show his exposures in [Bad] Nauheim. He is going to do so. For

the discussion, this issue seems to me to be the most important now. You are going

to be coming to Nauheim for sure, aren’t

you?[10]

132. To Edouard Guillaume

4 September 1920

Dear Guillaume,

The conclusion about the rate of the moving clock cannot be derived from the

formula[1]

. . . . . (1)

It rather results directly from the inverse Lorentz transformation:

For the pointlike events that correspond to the ticking of a clock indicating seconds

positioned at the origin of K , is

The result is therefore

.

From this, one may not by any means conclude that “the clock that indicates t is

running more slowly than the one that indicates t .” Rather, t is indicated by many

clocks and, to be precise, by each clock at rest relative to K that just coincides with

the nth tick of the clock positioned at the origin of K . I see from this statement of

yours that you have still not fully grasped the special theory of relativity, i.e., the

theory of 1905, misunderstandings prevail instead. A single clock can only mea-

sure the time at a single location (of the frame of reference). In time evaluations in

which many locations (with reference to the coordinate system) are involved, a sys-

tem of set clocks is always necessary.

t t 1 cos + =

t

t

v-x

c2

---- +

1

v2

c2

---- -–

------------------- -=

t n ( whole number = =

x 0.=

t

n

1

v2

c2

---- -–

------------------ =