D O C U M E N T 6 5 F E B R U A R Y 1 9 2 1 5 5
of course, causally determined only insofar as it exhibits characteristics indepen-
dent of the choice of a coordinate system. Questions such as where does the grav-
itational field that forms when I set the coordinate system into rotation come from?
are therefore senseless.
Experiments like the one you suggest are, in
principle,[3]
thoroughly legitimate.
The gen. theory of relativity allows an exact calculation of the result in advance.
Unfortunately, all the effects coming into consideration here enter into the factor:
gravitational constant/square of the velocity of light, which is of order of magni-
tude
10–28
and causes these effects not to be attainable by laboratory experiment
because of their
smallness.[4]
In gr. respect.
65. From Paul Oppenheim
Frankfurt am M[ain], 46 Guiollett Street, 25 February 1921
My dear Professor,
I had just written the enclosed protest letter to Mr.
Fabre[1]
when his book
arrived, which I send you herewith. My letter is thus, unfortunately, outdated and I
ask you now please kindly to let me know what I ought to write with regard to pages
15–18.[2]
I find the author’s whole proceedings obnoxious and his enthusiasm is
absolutely no excuse; I rather see in this an unacceptable exploitation of your name
for commercial purposes, as it has unfortunately probably not been the first time. I
am, naturally, innocent of the whole indiscretion, otherwise I would be even more
annoyed about
it.[3]
I would, of course, not like to answer Mr. Fabre’s letter, which
I received before my trip to Berlin, before I have your response about what to write
him, and would therefore be obliged to you if you let me know as soon as possible
what and how I ought to reply. I would naturally very much prefer it if you wrote
him directly; for one can see from this case what can happen when someone stands
in-between, even when he, like I, is so careful and devoted to you; one formal rea-
son you can have for writing him directly is the fact that I forwarded a copy of his
letter at his request. If, however, you for any reason prefer not to correspond with
such a person directly anymore, please feel free to make use of my services as inter-
mediary. One could also consider sending out my letter as if I had not yet received
his book; I would not find this altogether unprincipled, as I had demonstrably writ-
ten him before receipt of the work. If you think this approach practicable, I request
that you return my letter addressed to Mr. Fabre: otherwise, please destroy it. If you
would like to read the book itself before returning it to me, there is, of course,
plenty of time for that.