Abstract: When looking at large scale maps of the distribution of galaxies around our position is space it may be noticed that there seem to be finger like structures of these galaxies pointing back at the earth. This is called the Fingers of God (FOG) effect.  Some creationists have attempted to use this as an argument for an absolute geocentric universe. But the FOG effect can be simply explained by reasonable assumptions on the dynamics of galaxies within their clusters. Therefore it would be very naïve to use it as evidence in support of a galactocentric universe or an absolute geocentric universe. (This article is somewhat technical. First published in the Journal of Creation 22(2):75-78, 2008; edited here.)

Introduction

Highlighted in red is a galaxy cluster plotted in direction on the sky and redshift (written in units of velocity (km/s)). The FOG effect is clearly seen in redshift space. Earth is at the apex of the pie slice. The argument is that the FOG effect results only in redshift space and not in real space when the intra-cluster motions of the constituent galaxies are properly taken into account.

On occasion I have heard discussed among creationists, that considered the Fingers of God (FOG) effect as evidence for a galactocentric¹ universe and some foolishly even considered it evidence in favour of a geocentric² universe.  The phenomenon is well known and in Wikipedia it is reported.

“Redshift-space distortions are an effect in observational cosmology where the spatial distribution of galaxies appears squashed and distorted when their positions are plotted in redshift-space (i.e. as a function of their redshift) rather than in real-space (as a function of their actual distance). The effect is due to the peculiar velocities of the galaxies causing a Doppler shift in addition to the redshift caused by the cosmological expansion.”³

From this it would seem that the FOG effect results from Doppler motion of galaxies within their clusters causing a line of sight effect in redshift space⁴ (explained below), which produces the effect of fingers of galaxies all pointing towards the observer if plotted on a map. But if one realizes that we cannot definitively know how galaxies in the Universe are distributed without making certain assumptions, then how can one use this effect as evidence for a galactocentric universe or even a geocentric universe?

Galaxies clusters are observed with constituent galaxies numbering in the thousands. It does not seem to be unreasonable to assume that within those clusters the galaxies have random orbit trajectories, meaning they orbit around their common centre with different trajectories. Generally clusters appear to be approximately spheroidal or elliptical in shape. And they are believed to be viralised.⁵  If the mass of the cluster, which includes large quantities of hot intercluster gas comprising about 3 to 4 times the mass of the constituent galaxies, is in hydrodynamic equilibrium then the galaxies are mutually bound to each other. This means on the Hubble timescale or the usually stated age of the universe,⁶ more than ten billion of years, the cluster will not break up. Using this fact, astrophysicists estimate the dynamical mass of the cluster by either measuring the temperature of the x-ray emitting gas or calculating the dispersion⁷ of a number of constituent galaxies, which act as tracers. This makes the implicit assumption that the galaxy clusters have had sufficient time in the Universe to come into dynamical equilibrium. Continue reading →