This question is about(adsbygoogle = window.adsbygoogle || []).push({}); empiricaldifferences in certain interpretations of the Hubble expansion. Not counting integral Weyl geometry there is basically only two, the only two that I am considering here.

1) Standard interpretation

2) Relativistic recession of condensed mass in space-time for whatever reason. Similar to assuming some version of the Big bang was an event in space-time rather than of space-time.

At first glance the answer might seem obvious. I mostly aware of the immense strengths of the Standard Model of Cosmology and the minor weaknesses. I am only interested in empirical differences though. The most obvious assumption is the isotropy of redshift z vs relative apparent brightness. However, consider the effects of Special Relativity. Leave the solar system in the direction of a distant galaxy at 86.6% the speed of light. The relative distance d becomes d/2, and the Hubble shift is reduced by 1. The peculiar redshift would be identifiable regardless of which interpretation is used. The relative brightness would also increase but by 86.6% rather than 50%. The opposite would obviously happen in the other direct and to varying degrees in between. This difference 86.6% vs 50% might seem to be a smoking gun until we look we actually look at a http://www.physicstoday.org/pt/vol-54/iss-6/p17.html" [Broken]. It seems that in general this is exactly what we see. It then seems that this isotropy we see would apply regardless of our peculiar motion. The anisotropy that we would see in redshift distribution would be common to both models. Note that the graph as a function of z is in comoving coordinates.

I understand that dynamically it's not very reasonable to describe the Big Bang as an explosion in the usual sense. Again, I am only interested in empirical differences. In what way can we say the assumption that the Big Bang created space itself is more than an ontological statement lacking empirical components outside of our models. Is it in fact a purely model dependent determination?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# The Robertson-Walker Metric

**Physics Forums | Science Articles, Homework Help, Discussion**