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Title: Does the proton-to-electron mass ratio vary in time or space?
Plain: Molecular vibrations depend on the ratio of proton to electron mass, while atomic transitions mostly do not, so comparing them tests whether this ratio changes. Both laboratory molecular clocks and ancient molecular absorption in distant galaxies are used.
Precise: Determine whether $\mu = m_p/m_e$ varies, either as $d\ln(\mu)/dt$ today from comparisons of molecular (for example HD+, H2+, N2+, Sr2) and atomic clocks, or as $\Delta \mu/\mu$ at redshift $z > 1$ from H2 and CH3OH absorption, at the $1e-17$ per year and $1e-7$ levels respectively.
Settled by: A molecular-clock to atomic-clock ratio tracked for several years with fractional uncertainty below 1e-17, or a radio methanol absorption measurement with sub-1e-7 precision.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: open
Status note: (empty)
Posed since: (empty)