1 8 6 D O C U M E N T 4 7 J U N E 1 9 2 0
47. To Moritz Schlick
[Berlin,] 7 June 1920
Dear Mr. Schlick,
This morning I received your friendly letter and your
manuscript.[1]
The situa-
tion surrounding the invitation to the philosophers’ congress is considerably differ-
ent from what the cunning Vaihinger led you to believe. He wanted to know whom
among those knowledgeable in the theory he could also invite; so I naturally gave
him your name. But there is no question of my having requested your or any one
else’s attendance in Halle. The whole business had little attraction for me and I was
glad to have a valid excuse to avoid all that palaver
there.[2]
Now some remarks about your wonderfully clearly written
manuscript.[3]
I
agree almost, but not quite completely, with your interpretation of
causality.[4]
Assume for a moment that we were familiar with gravitation only through the
movements of comets that passed by in (single) hyperbolic orbits diverted by the
Sun. Let it furthermore never happen that two comets have even approximately the
same orbital elements, hence that repetitions of the same events do not occur.
Couldn’t we then conceive of the event as causal? Certainly! One would draw the
laws, for inst., those corresponding to Kepler’s laws, hypothetically from a few cas-
es. Then they would subsequently be confirmed and every scientist would assign to
these laws the character of a natural law, even though any repetition of the same
occurrence was never observed. The whole empirical world could, in principle, be
thus composed, without our having to give up our causality principle, although we
might have been less prone to test it.
Furthermore, the problem of the law of inertia violating the causality postulate.
You legitimately pointed out in your little book that I had gone too far in that
exposition.[5]
But I cannot concede to your current construction of the facts.
According to my view, it would be correct to say: Newtonian physics must ac-
knowledge the objective reality of acceleration, irrespective of the system of coor-
dinates. This is possible only if one regards absolute space (or the ether) as
something real. Newton consistently does this as well.
You, however, simply say: Form is not an event. It is not “form” that is involved,
but the “persistence of a form.” I must reply: persistent equilibrium in a specific
form certainly is an event in the physical sense. Rest is a dynamic event in which
the velocities are constantly zero, one that for our consideration is, in principle,
equivalent to any other event of motion. As a matter of fact, dynamic events do take
place differently with respect to both rotating celestial bodies as well. (E.g.,
Foucault’s pendulum, a moon’s orbit, etc.)
Whether, in order to lend reality to acceleration, you call that which you need