7, Sentier des Lapins
19 July 1939
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A few months ago a Dutch newspaper carried a report which sounded comparatively intelligent that you have discovered something important about the connection between gravitation and matter waves. I would be terribly interested in that because I have really believed for a long time that the ψ-waves are to be identified with waves representing disturbances of the gravitational potential; not, of course, with those you studied first, but rather with ones that transport real mass, i.e. a non-vanishing Tik. That is, I believe that one has to introduce matter into the abstract general theory of relativity, which contains the Tik only as “asylum ignorantiae” (to use your own expression), not as mass points or something like that, but rather, shall we say, as quantized gravitational waves. I have done a good many calculations on this point but have found out very little, except that § 13.7 of Eddington’s book “Protons and Electrons”, which had fascinated me very much, is false. But it is unfortunately not very hard to find major errors in this ingenious book.
It’s a shame that I had to fill so much of this letter with uninteresting personal things about myself, but it is really so terribly hard to write, (I mean about such things as those just above).
If this letter reaches you on your sailboat I wish you much rest and enjoyment there. I am wonderfully well off here on the charming Belgian shore with these delightful people, happy as children. If one could only be somewhat more light-hearted and could think less about what is to become of oneself. Vacations are fine, but a vacation for which one cannot perceive a definite end is a peculiar thing.
Best regards from