Another Busy Day So, Letters from Einstein and Weyl

As given, with  the introduction by Peter Pesic, in Chapter 2 of  "Mind and nature: Selected writings on philosophy, mathematics, and physics"  Hermann Weyl

Two Letters by Einstein and Weyl on a Metaphysical Question

1922

[In May 1922 the French physicist Paul Langevin gave three lectures in Zurich on Einstein’s relativity theory, the first of which was such a thunderous success that the journalist E. Bovet posed an “easy question” to Langevin: “How can we explain the enthusiasm of the public, which—apart from a few exceptions—surely understood no more of relativity theory than I? Is this pure snobbery? Courtesy to a foreign scholar? Or is it explained through the surmise of a fundamental alteration in our view of the world? Would such a surmise be legitimate? If so, in what sense? Does relativity theory perhaps signify liberation from the mechanistic, materialistic view of the world, under whose pressure our modern culture is breaking up?” Though Langevin did not answer Bovet’s personal appeal, Einstein and Weyl did reply.]

Berlin, June 7, 1922

Haberlandstrasse 5

Dear Sir,

Your “Question to Mr. Langevin” provokes me to give an answer. Regarding the general questions that interest you, relativity theory changes nothing at all in the state of affairs because it signifies nothing but an improvement and modification of the basis of the physical-causal world-picture without a change in its fundamental point of view. This is a kind of logical system for representing space-time events in which mental essences (will, feeling, etc.) do not apply directly. To avoid a collision between the various sorts of“realities” that physics and psychology deal with, Spinoza and Fechner respectively founded the theory of psychophysical parallelism, which, quite frankly, completely pleases me.

Physics signifies one possible way among others equally justified to put experience in a certain order. The foundations of this system are freely chosen by us, namely from the point of view that at

any given time satisfies known facts with a minimum of hypotheses. Thus, this is not a matter of “believing,” but rather of free choice from the point of view of logical completeness and adaptability to experience, as indeed is so beautifully shown in the cited passages from Henri Poincaré.

The question “what is the use?” only means something—if it is really supposed to have a clear meaning—when completed by an expression signifying for whom, or even better for the satisfaction of whose wish, the thing in question may serve. I really cannot say more than this truism.

A. Einstein

Zurich, July 27, 1922

Dear Sir,

Mr. Bovet’s question, to which you invited me to reply, surprised me in two ways. First, that even today, after Western intellectual life has striven for one hundred fifty years to overcome the primitive position of the Enlightenment, that the strict lawfulness of the world of appearances can seem oppressive to the evaluating, willing, and active ego. And second, that Einsteinian dynamics, which only allows the energy and momentum of a body to depend on its velocity a little differently than Newtonian mechanics, is associated with the expectation of an easing of this pressure. Thus, as Mr. Bovet puts the question, one must unhesitatingly answer it in the negative; the inexorability of rational mechanics cannot be mitigated through the new view of things. Even a living organism, a rational being, can only put itself in uniform rectilinear motion like any mechanical system by pushing itself away from other bodies, to which it thereby gives an equal and opposite momentum. Yet it appears to me that physics has no far-reaching meaning for reality, just as formal logic, for example, has no far-reaching meaning in the realm of truth. The foundation of the truth of a judgment lies in the judged thing and not in logic. Every truth in itself is founded with regard to its contents, and (when perceiving) we try to seize this foundation in the depths, through insight, through intuitive reason. Nevertheless, the surface relations, which logic treats, govern the particular truths. But a gagging of the truth-establishing power, of reason, by no means lies therein. In an equal sense, a certain formal constitution of reality is pronounced in the physical laws. These laws will be violated in reality just as little as there are truths not in accord with logic, but these laws do not matter for the essential contents of reality; the ground of reality is not grasped by them. Of course, they do not allow free rein to every whim and caprice, but nothing hinders us from understanding them as surface aspects of a necessity that is “not of this world” and whose reality-grounding power we believe we feel in our moral wills. Likewise, in the domain of knowledge: if, for example, I judge “2+2 is 4,” then I believe that this judgment does not come purely from natural causality in my brain making it so, but instead because the factually existing circumstance 2+2=4—thus something not part of the things and forces of reality—has influence on my judgment.

But you do not wish to hear my philosophical point of view about the problem of causality; instead, you want information about whether the new development of physics has brought with it a shift in our understanding of natural causality. This I would like to affirm, yet this transformation does not come from relativity theory but from the modern atomic physics of matter. So far as I can judge, most physicists no longer believe in a “Laplacian world-formula,” in causality in the sense that,following simple and rigorously valid mathematical laws, which are investigated once and for all, the state of the cosmos at one moment unequivocally determines its complete past and future.  In physics today, we place atomic matter over against the “ether” or the “field” as the space-time extended medium that transmits the action from material particle to material particle. The sole ultimate constituents of matter are not, like ether, somewhat spatially extended, but each of them simply is inserted into a spatial field-neighborhood from which its field-actions emerge. The “ether”—which one ought not represent to oneself in the image of a substance—joins together all these material individuals into the active whole of a single external world. The cause of the field-states lies in matter; for example, light, which is a field phenomenon, is being excited, is being sent forth from matter. And today it seems as though rigorous laws underlie the propagation of action in the ether—with whose arrangement field-physics occupies itself—as though we can only establish statistical uniformities about how matter causes field-states; the entire physics of matter is statistical in nature.

According to the view sketched here, matter appears as an agent[agens] that, by virtue of its essence, lies beyond space and time. This agent composed of innumerable unconnected individuals we call “matter,” so far as we consider it as the cause of the actions spreading out in the field by which the

individuals weave together a world. According to its inner condition, this agent may just as well be creative life and will as matter.

H. Weyl

OK, so, you know me and that I can't resist making a comment.   Compare the ease with which Einstein and Weyl discuss philosophy and the flippant dismissal of philosophy by physicists and some mathematicians in subsequent generations of those professions and, as some philosophers, such as Dennett, hanker after the elan, glamour and faith bodies gained by science, even philosophers, today.