Gravity as Archimedes' thrust and a bifurcation in that theory

Abstract

Euler's interpretation of Newton's gravity (NG) as Archimedes' thrust in a fluid ether is presented in some detail. Then a semi-heuristic mechanism for gravity, close to Euler's, is recalled and compared with the latter. None of these two "gravitational ethers" can obey classical mechanics. This is logical since the ether defines the very reference frame, in which mechanics is defined. This concept is used to build a scalar theory of gravity: NG corresponds to an incompressible ether, a compressible ether leads to gravitational waves. In the Lorentz-Poincar\'e version, special relativity is compatible with the ether, but, with the heterogeneous ether of gravity, it applies only locally. A correspondence between metrical effects of uniform motion and gravitation is assumed, yet in two possible versions (one is new). Dynamics is based on a (non-trivial) extension of Newton's second law. The observational status for the theory with the older version of the correspondence is summarized.Comment: 24 pages, invited contribution to the Franco Selleri Festschrift, to appear in Found. Physics. v3: Endnote 45 on absolute simultaneity improved (formerly footnote 6: class file changed to revtex4), a few references updated (and now with titles). v2: minor correction in subsect. 3.2, some wording improvements, and a few references adde