IMG51

Ernst Mach

this time as a rcgular or ordinarius profcssor.²² By thcn, howcvcr, Einstein had already receivcd what might easily bc interpreted as dircct privatc and public support from Ernst Mach himsclf.

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■ A few wccks bcforc Einstein was to givc an eagcrly awaited Iccturc ! on relativity in Salzburg in September 1909 hc received a book from : Ernst Mach in the mail.^2,1 It was a ncw German edition of his Con-sewation of Energy, and it includcd the following rcfcrcncc to rclativity and rcccnt work by Minkowski, who had placcd Einstcin’s special theory within a four-dimcnsional contcxt: “Space and timc arc not herc conceived as independent entities, but as forms of the dcpcndcncc of the phenomena on one another. 1 stibscribe, thcn, to the principlc of rclativity, which is also firmly upheld in my Medianies and Wannę-lehre (H. Minkowski, Katan ur.d Zeit, Leipzig, 1909).” ²¹ We do not know if Einstein or many readers of the book noticed Mach’s attempt to link Minkowski with Mach’s own epistcmological theory of relativity, but at the vcry least the passage did suggest that Mach was interrsted in and vcry likcly was kindly disposc.dj&waJld Einstein’* and Minkowski’s notions of physical rclativity.²⁵ Einstein thankcd Mach for the book in a letter dated August 9, 1909, and de-clared that he had already rcad Mach’s Conseroation of Energy with care as wcll as his Mechanics. Hc added that Mach had great influence among the younger generation of physicists and that he pcrsonally sympathized with him in his currcnt disputc with Max Planck.²® (That Machs influence among older physicists was also large at this timc is confirmcd by Ernst Lcchcr, Mach’s succcssor at Prnguc. who wrotc in January 1910 that "Natural scicntists arc for the most part followcrs of Mach, but not so the professional philosophers.”) ²⁷ Mach replied in a letter which has sińce become lost. (Ali the Mach side of the Mach-Einstcin corrcspondencc is missing.) The letter. how-:ever, must havc included something favorahle about the theory of rclativiiy bccausc on August 17, only cight days after his first letter,

I Einstein wrotc to Mach again, thanking him, among other things, for his favorablc attitudc toward the theory: "Your fricndly letter has plcascd rne enormously as has yout treatise. ... I admirc your great energy. It sccms that I forgot to send you my treatises fwhich had bccn promiscd in the p. vious letter], but they will now accompany

this [post]card. It plcases mc grcntly, that you takc plc3surc [Vcr-gnugen] in the theory of rclativity. . . .”²⁸

The cxact naturę of Mach'.? “plcasurc" is unclcar, but two of Machs articlcs, both published in 1910, did cx press a brief if rather eryptie adrr.iration for the work of Einstein and Minkowski:

Similarly, one will have to disringuish between metrical and pjiysical (timc containing) space, as has already bcen suggested in my Comcraańon of Energy and in TCńowledge and Error. . . . Esscmial progress in this | direction has bcen instituted and carricd out by A. Einstein and H. Minkowski.²⁰

If the kinctic vcrsion of the physical world picturc, which in any case I consider hypothctical, without intending thereby to degradc it, wcrc to “cxplain" all physical appcaranccs, I would still not consider the manifold-edness of the world to be cxhaustcd, sińce for me matter, time, and space would still be problcms, a vicw which the physicists (Lorentz, Einstein, Minkowski) arc gradually approaching.³⁰

Philipp Frank visited Mach in Viennn during that same year (1910) and departed with the fceling that he dcflnitely accepted the theory of rclativity: “I had the impression at that timc that he agreed complctely with Einstein’.? special theory and espccially with its philosophical basis.”³¹ Einstein also visitcd Mach, but the meeting was short and the exact datę unclear. though it was probably around 1910. Einstein vainly tried to persuade the older man to acccpt Boltzmann’s approach to atomism.³² Einstein never publicly recallcd that their conversation had touched on the question of relativity, which suggests cither that the subject was not discussed or that Mach tended to be cv.isive or noncommittal. If Mach had announeed any strong opinion. favorable or unfavorable, Einstein would surcly have remembered it. On the other hand, thcrc is no cvidcnce to believe that Einstein s notion that Mach at least sympathized with the special theory was in any way challcngcd or destroyed. Einstein clearly continued to imagine that on the morc important points Mach was and rcmained his scientific and philosophical ally.³⁸

Einstein was not unhappy at the Univcrsity of Praguc. In spite of having to dress “likc a Brazilian admirał” for his oath of allegiance ccremony on bccoming an Austrian profcssor. working in an office overlooking a park for the insanc, and living in a city with so much unpleasantness between nationalities and culturc groups. he sccms to havc bcen reasonably satisficd.^łł 1 lis wifc, howcvcr, and an ofler from

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