Rotary closed-cycle externally-heated engine

Disclosed is an apparatus, system, and method, by which a difference in the thermal energies, and/or temperatures, of two bodies, materials, gases, liquids, solids, objects, and/or other groups or collections of matter, may be harnessed to provide mechanical energy to a rotary engine and/or shaft. Also disclosed is an apparatus, system, and method, by which mechanical energy (e.g., the rotation of a shaft) may be used to produce and/or amplify a difference in the thermal energies, and/or temperatures of, and/or between, two bodies, materials, gases, liquids, solids, objects, and/or other groups or collections of matter. The disclosed thermal-to-mechanical energy conversion apparatus, as well as the complementary mechanical-to-thermal energy conversion apparatus, lacks moving parts and therefore satisfies a previously unmet need for a simple, robust, and efficient heat engine.