A stringent limit on a drifting proton-to-electron mass ratio from alcohol in the early Universe
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The standard model of physics is built on the fundamental constants of nature, but it does not provide an explanation for their values, nor requires their constancy over space and time. Here, we set a limit on a possible cosmological variation of the proton-to-electron mass ratio μ by comparing transitions in methanol observed in the early universe with those measured in the laboratory. Based on radio-astronomical observations of PKS1830-211, we deduced a constraint of ∆μ/μ = (0.0 ± 1.0) × 10−7 at redshift z = 0.89, corresponding to a look-back time of 7 billion years. This is consistent with a null result.