Tim Thompson

2002-Oct-14, 12:13 AM

One of the key aspect of many alternate cosmologies is a powerful desire to do away with the redshift distance relationship. This is prominent, for instance, in the Quasars Far Away (http://www.badastronomy.com/phpBB/viewtopic.php?topic=2378&forum=1&137) thread.

But the redshift distance relationship does not exist in a "vacuum" (of the intellectual type). Why did Hubble (http://www-gap.dcs.st-and.ac.uk/~history/Mathematicians/Hubble.html) come up with it in the first place? Because he realized that galaxies of the same type in the Hubble classification of galaxies (http://casswww.ucsd.edu/public/tutorial/Galaxies.html) showed brightness correlated with redshift; dimmer galaxies have larger redshift. If one makes the fairly benign assumption that galaxies of the same type are of approximately the same intrinsic brightness (say within a factor of 2 or so), then dimmer means farther away. And so redshift means farther away too. And so the redshift distance relationship was born.

But that's not the only correlation. There are several other indicators of distance. Aside from the well known Cepheid variable stars, there are also surface brightness fluctuations, the Tully-Fisher relation, type Ia supernovae, and a few others.

The relevance here is that they are all correlated together, and especially with redshift. If redshift does not correlate with distance, then how can it correlate so well to several other measured parameters, which also should correlate with distance in the same way?

One cannot speak of throwing out the redshift distance relationship, without also throwing out everything we know about cosmological distances. This point should be adressed, but almost never is addressed, by those who wish to eliminate the correlation between redshift & distance.

Reference: A Critical Review of Selected Techniques for Measuring Extragalactic Distances (http://nedwww.ipac.caltech.edu/level5/Jacoby/Jacoby_abstract.html), G.h. Jacoby et al., Publications of the Astronomical Society of the Pacific 104: 599-662, August 1992.

But the redshift distance relationship does not exist in a "vacuum" (of the intellectual type). Why did Hubble (http://www-gap.dcs.st-and.ac.uk/~history/Mathematicians/Hubble.html) come up with it in the first place? Because he realized that galaxies of the same type in the Hubble classification of galaxies (http://casswww.ucsd.edu/public/tutorial/Galaxies.html) showed brightness correlated with redshift; dimmer galaxies have larger redshift. If one makes the fairly benign assumption that galaxies of the same type are of approximately the same intrinsic brightness (say within a factor of 2 or so), then dimmer means farther away. And so redshift means farther away too. And so the redshift distance relationship was born.

But that's not the only correlation. There are several other indicators of distance. Aside from the well known Cepheid variable stars, there are also surface brightness fluctuations, the Tully-Fisher relation, type Ia supernovae, and a few others.

The relevance here is that they are all correlated together, and especially with redshift. If redshift does not correlate with distance, then how can it correlate so well to several other measured parameters, which also should correlate with distance in the same way?

One cannot speak of throwing out the redshift distance relationship, without also throwing out everything we know about cosmological distances. This point should be adressed, but almost never is addressed, by those who wish to eliminate the correlation between redshift & distance.

Reference: A Critical Review of Selected Techniques for Measuring Extragalactic Distances (http://nedwww.ipac.caltech.edu/level5/Jacoby/Jacoby_abstract.html), G.h. Jacoby et al., Publications of the Astronomical Society of the Pacific 104: 599-662, August 1992.