EINSTEIN, Albert (1879-1955). Typed letter signed (''A. Einstein'') to Daniel M. Lipkin, Princeton, 13 October 1952. [With:] an enclosure, being Lipkin's letter to Einstein, Philadelphia, 7 October 1952 bearing Einstein's autograph marginalia and a...

EINSTEIN, Albert (1879-1955). Typed letter signed ("A. Einstein") to Daniel M. Lipkin, Princeton, 13 October 1952. [With:] an enclosure, being Lipkin's letter to Einstein, Philadelphia, 7 October 1952 bearing Einstein's autograph marginalia and a lengthy autograph note signed ("A.E") at the letter's conclusion.

Partly in German. One page, 166 x 141mm; enclosure, five pages, 280 x 215mm, with Einstein's holograph comments in German transcribed in type below by the correspondent (minor smears to ink).

Einstein offers his comments on a lengthy question on space time and the nature of observation from a former student of David Bohm at Princeton. Einstein offers a running commentary on Lipkin's five-page letter discussing the distinction "between two classes of mathematical entities", namely those "which refer mainly to the observer's particular coordinate system and which cannot be given any direct physical interpretation; then on the other hand there are physically meaningful field-components." As Lipkin elaborates on his line of reasoning, Einstein adds his comments in the left margin, most often a simple "no!", sometimes a "yes" and occasionally a "?". In one instance, Lipkin raises "a very delicate point" stating that "one could take the point of view that free-space equations Rik = 0 of the General Theory of Relativity are phenomenological!" Einstein underlines the last two words and adds a question mark while commenting that Lipkin's term has "no clear meaning". Einstein agrees with the balance of Lipkin's reasoning in this passage, which leads him to considering the consequences of the premise, "that the Theory of Generalized Gravitation provides an accurate description of all possible physical facts." To this, Einstein adds: "This is what I hope for". While Einstein offers comments to the first three pages, he tapers off in the fourth and fifth, the latter of which he pens a short note in German, responding to Lipkin's conclusions concerning the potential for hypercomplex numbers for "obtaining solutions to the general field-equations". To this Einstein, still more comfortable writing in his native German, writes: "I can imagine that the field might be conceived as a hypercomplex number that appear as a function of another hyper-complex number (which would represent 'coordination space'). But I doubt whether one could thus arrive at a system which could express general covariance. The theory of complex functions (two-dimensional) seems to me to prove your analogy, because the equation ... Is not a general covariant equation."