... clustered. (Of course, the random arrangement canproduce fluctuations, accidental groupings; by random, and not clustered, wemean clumped no more than would be expected on average by chance.) ... of Mg+ to thatof a line of H can be used to determine whether the ratio of electron to protonmass is changing in time. With what accuracies do the line wavelengths need to be measured to rule ... of redshift alone can be used, togetherwith Hubble’s law, to obtain the distance to a galaxy, provided that the galaxyis far enough away for the contribution of random velocities to the redshift...