D O C U M E N T 3 4 J A N U A R Y 1 9 2 1 2 9
I have learnt from my
friends[3]
that our Russian friends are performing intensive
scientific work even in the present conditions.
I am fully convinced that it is the pleasant and holy duty of all scientists who live
in better conditions to help Russian colleagues, and that they will do their best to
restore international scientific contacts.
I cordially greet our Russian friends and promise to do what I can to establish
and preserve contacts between scientists here and in Russia.
A. Einstein.
Translator’s note: Translated from Russian by Frenkel (1976) and József D. Illy.
34. To Edouard Guillaume
[Berlin,] 27 January 1921
Dear Guillaume,
My comprehension of your exposition of Jan. 25th stops when you introduce the
variable
t.[1]
You write:
.
This variable t should not just relate to a specific worldline, but should have a
general meaning. Thus t = const is a line on the plane, t a parameter indepen-
dent of the considered
worldline. Now, the quo-
tient has at one place
P a specific value for the
considered worldline. But
if I draw a second world-
line (II) through P, then for
this one has a differ-
ent value from the one for the first worldline.
Now you set . In this equation, after what has just been said, and
cannot both be only dependent on the location, because is not a de-
fined quantity for P but depends on the direction of the worldline drawn through P.
dx1
d
1
------- -
dx1
dt
------- --------
dt
d
1
- =
x1,
1
worldline
worldline II
1
x1
t const t = =
P t const t dt + = =
dt
d
1
------- -
dt
d
1
------- -
dt
d
1
------- -
c0
c1
---- - = c0
c1
c0
c1
---- -
dt
d
1
------- - =
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