Friday, December 10, 2010

On aiming too high

Apropos the final paragraph of my previous post - my purchase of "Cosmology" by Steven Weinberg, Roy Simpson observes:


The expressions are "bitten off more than you can chew" and - perhaps more appropriately - "eyes larger than stomach" (I blame the Amazon science marketing department myself who really need to know your level of expertise and interests - I have looked at the Amazon entry for the book.) The problem here is that Weinberg has already written a book:--

Gravitation and Cosmology (1972)

which introduces gravitation and applies to cosmology.
[Note: costing £120!]

The 1972 book takes about 150 pages to reach Einstein's equations and about 400 pages to reach the Robinson-Walker metric with which your current book begins. So the present book is a "what happened next" - an update 35 years later. So the basics are in the 1972 book which he didn't repeat, although there is an equation summary of that book in Appendix B.

The present book is about things like inertial anisotropy (i.e. irregularities, perturbations from the symmetric Robinson-Walker metric) rather than the core theory. I suspect that this book is for experts in particular contemporary subfields to get hold of specific derivations and data rather than a "read through".

Furthermore I see that the present book (and the 1972 book too I think) are about mainstream Cosmology. This is OK for the purposes above, but if a reader wants some Cosmological excitement in their life, they may have to look elsewhere. One day, for example, in amongst all these Tensors you might learn about something called Torsion.

Torsion is a spin-like property of Tensors which is set = 0 by Einstein (so it is a little bit like the more famous Cosmological Constant Λ, also set = 0 initially). A theory was later developed as a generalisation of Einstein's equations including Torsion, but I cannot see a reference to Torsion in the Index to the 1972 book - when the theory was a live minor alternative to GR.

You can check the present book just in case he refers to it here, but studying what I can of the equations on Amazon I don't see the reference where I would expect it to be.

So I just hope that you have substantially more free bookshelf space than me!



Yes, I wanted something which talked about the topology of the universe as well as the big bang and inflation. "Cosmology" does discuss all these questions, it's not so "bitty" as you imply, but at a sophisticated level. It's billed as a graduate textbook (which is where I take myself to be: beginning-graduate student) but on scanning it last night I don't think Weinberg intended it for self-study.

I intend to treat it as a target, something the other side of all that differential geometry, tensor analysis and GR. I find that quite motivational, actually.