Redshift quantization is the hypothesis that the redshifts of cosmologically distant objects (in particular galaxies) tend to cluster around multiples of some particular value. Since there is a correlation of distance and redshift as expressed in Hubble's Law, redshift quantization would either indicate a quantization of the distances of galaxies from the Earth or a problem with the redshift-distance correlation, either of which would have serious implications for cosmology. Many scientists who oppose the Big Bang theory, including Halton Arp, have referred to observations claimed to be in favor of redshift quantization as reason to reject the standard account of the origin and evolution of the universe.
In 1973, astronomer William G. Tifft was the first to report evidence of such clustering (before that see György Paál). Recent redshift surveys of quasars (QSOs) have produced no evidence of quantization in excess of what is expected due to galaxy clustering, and consequently most cosmologists dispute the existence of redshift quantization beyond a minimal trace due to the distribution of galaxies across voids and filaments.
"Redshift quantization" has also been called redshift periodicity, redshift discretization, preferred redshifts, and redshift-magnitude bands.
Read more about Redshift Quantization: Original Investigation By William G. Tifft, Subsequent Work By Other Researchers, Evaluation and Criticism