D O C U M E N T 4 8 J U N E 1 9 2 0 1 8 7
absolute space, the ether, or a preferred system of coordinates, is all the same (al-
though one would probably not want to incorporate the last of these into the causal
series as something real). The unsatisfactory situation remains that this something
enters only one-sidedly into the causal series. Whether one can declare the law of
causality satisfied or not depends on the subtleties of the definition of the law of
causality. Newton’s absolute space is independent, uninfluenceable by anything,
the -field of the general theory of relativity is subject to the laws of nature, (not
just determining, but) determined by the properties of matter. This you expressed
masterfully, by the way, on page
Re page 28 top. It seems to me unjustified to state that gravitational fields should
not be regarded as observable in the same sense as
the “process
characteristic” of the latter seems unessential in this connection. What is essential
is that one absolutely cannot speak of “all characteristics” of a body (because there
are many of them); if it belongs within a theoretical system, there are always
properties that are a consequence of the others, regardless of whether this system
operates with “processes” or whether it makes do with static considerations (this
difference does not seem to me one of principle).
The restriction of causality to the ability to continue the givens within a spatial
section is not my meaning; however, that viewpoint is in any case
is not necessary to describe an extension of the natural laws beyond that—should
it ever prove possible—as an extension of causal knowledge. But why not do so?
Just in order to single out time? It may very well be possible that a free choice of
initial conditions that leave room for more developed natural laws will be much
more limited than seems to be the case from the current state of our knowledge.
Then one would also explain the lawfulness within the time section as a “causal”
one, in order not to make an unnecessary distinction between temporal and spatial
Your invitation pleased me very
If I can arrange it, I shall pay you and
your family a short visit. I do not think, though, that it will work, because I have to
be “stingy” with my time like a real European.
Cordial greetings to you and yours, from
A. Einstein.
48. To Robert Fricke
Berlin, 9 June 1920
Highly esteemed Colleague,
Your letter of 26 Jun. arrived in my hands late because I was away on a
Many thanks for your kind
In my opinion, though, our professional
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