Einstein writes to physicist–philosopher
Schlick (1882–1936), a professor of philosophy at the University of Rostock who was to become
a founder of the Vienna Circle of logical empiricists. Einstein is responding to an essay Schlick
wrote on special and general relativity shortly before the general theory was published in its
final form in November 1915. Einstein points out that relativity theory is a blow to the Kantian
doctrine that the human mind has a priori knowledge of some absolute truths about
the real world—for example, its supposed obedience to Euclidean geometry. For an extended
discussion of the philosophical issues and Einstein's friendship with Schlick, see the article
by Don Howard on page 34 of this issue.
Berlin, 14 December 1915
Highly honored colleague,
I received your paper yesterday, and
have studied it thoroughly. It's among the best yet of what's been written about relativity. Nothing
nearly as clear has previously been written about its philosophical aspects. At the same time you
have full command of the theory itself. . . .
Truly masterful is your discussion
of relativity theory's relationship to the philosophy of [Immanuel] Kant and his disciples. Their
trust in the "incontrovertible certainty" [apodiktische Gewissheit] of "a priori synthetic
judgments" is badly shaken by the recognition that even a single one of those judgments is invalid.
Your argument that positivism suggests the theory of relativity without requiring it is also very
right. You've also correctly recognized that this line of thought has had great influence on my
efforts, specifically [Ernst] Mach and, even more, [David] Hume, whose Treatise of Human Nature
I studied with passion and admiration shortly before discovering the [special] theory of relativity.
Very possibly, I wouldn't have come to the solution without those philosophical studies.
Your comments on the general theory
of relativity are also completely correct. . . . The new finding is that there
exists a theory, consistent with all observations thus far, whose equations are covariant under
arbitrary transformations of the space–time variables. One just has to regard the world
as a four-dimensional (hyperbolic) continuum. . . .
The empirical testability of the theory
is not entirely as dismal as you indicate. The theory explains quantitatively the motion of Mercury's
perihelion discovered [in 1855] by [Urbain] Leverrier. The influence of the gravitational potential
on the color of emitted light required by the theory has been qualitatively confirmed by astronomical
observation ([Erwin] Freundlich). There is also a good prospect for testing the theory's prediction
of the deflection of light rays by the gravitational field.
Asking you to visit me when your path
leads to Berlin, I remain your entirely devoted
A. Einstein
Reference
1. The Collected Papers of Albert Einstein, vol. 8A, R. Schulmann, A. J. Fox, J. Illy, eds., Princeton U. Press, Princeton, NJ (1998), p. 220.
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