Reinterpretation of the Michelson–Morley experiment and its consequences for cosmology

The Michelson–Morley (MM) interferometric experiment (Michelson and Morley [Am. J. Sci. 34, 333 (1887), doi:10.2475/ajs.s3-34.203.333]) is one of the most pivotal experiments in modern physics, originally designed to detect a hypothesized anisotropy in the speed of light in vacuum due to aether drift. Contrary to this expectation, we show that the MM-type experiments are inherently incapable of detecting such drift. Their null result arises naturally from the Doppler effect acting on the interfering light beams, even in a frame moving relative to the aether. Consequently, the existence of aether cannot be excluded by these experiments. This interpretation remains consistent with Einstein’s postulate of the constancy of the speed of light in vacuum, provided phase velocity, rather than group (signal) velocity, is considered. Our findings align with modern astrophysical and cosmological observations of the cosmic microwave background (CMB), which strongly suggest the existence of a preferred stationary reference frame. This reinterpretation of the MM experiment also resolves well-known paradoxes in Special Relativity.