Schutz and the Hubble Flow

In summary: I agree, it is quite a short and concise book, which can be both a positive and a negative depending on the reader's preferences.
  • #1
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TL;DR Summary
In the first edition of Schutz (1985), the author states that the Hubble flow can't make galaxies recede faster than the speed of light.
In the last chapter of Schutz devoted to Cosmology, Schutz writes
Moreover, ## v = Hd ## cannot be exact since, for ##d\gt 1.2 ~10^{26}~\rm{m}= 4000~ \rm{Mpc}##, the velocity exceeds the velocity of light!
So it seems that in 1985 it was assumed as obvious that the recession speed could not exceed ##c##.
The consensus seems to have swiftly changed. When did that happen? Was it debated at all?
 
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  • #2
I was still at primary school in 1985 so I can't speak to common beliefs, but I think Schutz isn't intending to be quite so emphatic as he sounds. I think he's criticising his cheap'n'cheerful derivation of the Hubble Law as being based on kinda-sorta Newtonian thinking. He expands a bit on it in a later paragraph. In the 2nd edition it's just before the section titled "The universe is accelerating!", but I suspect it might be the end of section 2.2 in your edition. It says "...in the attempt to translate the nonrelativistic formula ##v=Hd## into relativistic language, we were forced to re-think the meaning of all the terms in the equations and go back to the quantities we can directly measure."
 
  • #3
That paragraph is indeed in the 1st edition at section 2.3 (Cosmological observations). But, given that his book is titled 'A First Course in General Relativity', he could not possibly assume that the reader would understand that recession speeds >c are possible, especially after the quote I gave before. This was written at the time when we thought that the universe expansion must be slowing down, and the big question was why we were so close to the critical density. The quote suggests to me that the common understanding of the time was that recession speeds >c were impossible. But I have not been able to find any source that confirms or contradict my assumption and no trace of any debate in the scientific community about the topic.
 
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  • #5
phyzguy said:
In the excellent paper by Davis and Lineweaver, they list all of the people that have gotten this wrong, including some big names.
This includes the very quote we're discussing - see Appendix B item 6.
 
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  • #6
epovo said:
So it seems that in 1985 it was assumed as obvious that the recession speed could not exceed ##c##.
I don't think the reason is that in 1985 it was assumed as obvious that the velocity of the recession could not exceed c, because the quote is the same in the second edition (2009).

In fact, Schutz's quote is one of the common misconceptions in cosmology that Davis and Linewaver mention in their (highly recommended) article Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the universe (2003). See chapter 3.1 and Appendix B [6]
 
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  • #7
Thank you @Jaime Rudas . I'll be sure to read that article!
 
  • #8
I never understood what's the hype about Schutz's book...
 

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