 One interesting cause of such change would be change over time in the strength of the strong force.Astronomical searches for time-varying "μ" have typically examined the Lyman series and Werner transitions of molecular hydrogen which, given a sufficiently large redshift, occur in the optical region and so can be observed with ground-based spectrographs.If "μ" were to change, then the change in the wavelength "λi" of each rest frame wavelength can be parameterised as