New "derivation" of the redshift equation

Key reference is the monograph by Barry Setterfield: Cosmology and the Zero Point Energy (Natural Philosophy Alliance Monograph series, No.1, 2013, ISBN 978-1-304-19508-1).
I've been given the opportunity to inform Setterfield personally about the mathematical errors in Appendix A of the book, by email:
Dear Barry,

As promised, I've pinpointed some mathematical errors in your book.
And they are significant. I have said in my first email that it is
"not a minor issue". The errors in the mathematical formulas are a
serious threat to your theories, and they undermine the wording of
ideas that might have been worthwhile otherwise. But despite of all
this, there are still aspects in your work that I find trustworthy.

Sorry I have to inform you in this way, but that's the way science
works and the way it is demanded by just being honest. I would say:
keep breathing. Thanks for your data too. My personal bias is that
the universe in reality is much smaller and much younger and maybe
those data might help to find some "I did it my way" confirmation.

Best wishes,

Han
It would be impolite to disclose the answer given by Setterfield here, because it's part of private communication. But my own answer to it is not subject to such a restriction. So here comes.
Dear Barry,

Allright, I see that you've adopted a different strategy. Let's try to summarize it. It is supposed by you that the redshift is explained by the PPP, simply as: $$ 1+z = \frac{1+T}{\sqrt{1-T^2}} = \frac{1}{A-N} $$ Then indeed it follows that: $$ A-N = \frac{\sqrt{1-T^2}}{1+T} \\ T = \frac{1-(A-N)^2}{1+(A-N)^2} $$ The derivative as derived by you is correct: $$ \frac{dN}{dT} = \frac{1}{(1+T)\sqrt{1-T^2}} $$ And upon substitution of $T$ we find, indeed: $$ \frac{dN}{dT} = \frac{\left[1+(A-N)\right]^2}{4(A-N)} = \frac{1}{4(A-N)}+\frac{1}{2}(A-N)+\frac{1}{4}(A-N)^3 $$ Now the only problem is to bring this, term by term, in agreement with the PPP equation: $$ \frac{dN}{dT} = q - r\,N^2 $$ And yes, of course that is going to succeed if you assume that $q$ and $r$ are not constants but vary with $N$.
Since I'm playing the role of a pure mathematician here, I cannot judge if such is correct or not, so I'll give you the avantage of the doubt.
The mathematics could have been done in a more concise way, but this time I've found no errors in it. Well done!

Kind regards,

Han


The "Well done!" at the end must be regarded as a slip of the pen; I very much regret it. Indeed, strictly speaking, there are no errors in the mathematics anymore. But I happen to be a theoretical physicist by education as well. And when adopting that role, I can tell that the physical argument too is, let's say: not quite according to the rules of the discipline.
  1. Assume that the solution of the differential equation is the one that you want
  2. Then derive the differential equation that should supply the desired solution
  3. Make up some new laws of physics on the fly, in order to motivate the equation
Instead of trying to be impressive with "Appendix A: The ZPE and the redshift equation derivation" - which still is no derivation at all - it would have been more honest to simply declare the so much celebrated redshift equation as being a Hypothesis. Which is perfectly legal. No Appendix A. No fake proofs. Period.
Barry's "new derivation" of the redshift equation seems to be in concordance with the following entries on his website: