This is a beautiful book authored by Dennis Overbye. It is full of lovely biographical stories, which are nicely interwoven into the central story that is the history of cosmology in the last century, and even has some satisfying non-technical descriptions of cosmological physics. I only wish that it was published after the dark energy paradigm.

# Monthly Archives: February 2013

# Book review: The Constants of Nature

I picked up this book, which is authored by Cambridge’s John Barrow, from a second-hand bookshop in a wonderful little Vietnamese city called Hoi An. It was one of only two popular science books that I found and bought in Randy’s Book Xchange, but this bookshop-cum-house and its equally interesting American expatriate owner would have made the hazardous bike ride to get there worthwhile even without my two purchases.

As for the book, I suspect that its key points could be summarised in a terse two-page discussion article. The unnecessary repetitiveness of particular ideas and analogies made it more of a struggle to finish than it should have been. Also, the abundance of errors in this book, detailed in another review http://www.ams.org/notices/200410/rev-blank.pdf, were a further source of irritation.

The basic idea is interesting: what are the constants of nature and are they actually constant? However, for its lack of breadth, I think that there could have been more depth either in biographical or physical details. Alas, popular science books are designed for mass, spoon-fed consumption and perhaps therein lies the source of this criticism.

Near the end of the book Barrow spends some time discussing his research related to measuring variations in the fine structure constant through astrophysical observations. He claims to have measured, with Victor Flambaum and other collaborators, a statistically significant nonzero variation in the fine structure constant that is equal to, if I recall correctly, a few parts in a million over the lifetime of the universe. I’m not sure if these measurements have found an alternative explanation in the 11 years since the book was published–I spoke to Flambaum at the University of New South Wales last year and he seemed to still be very much interested in this line of research–but from an aesthetic point of view I find such tiny variations to be ugly and I predict (or possibly retrodict) them to be due to some form of bias. Such aesthetic considerations aren’t always the most important–the ‘unnatural’ smallness of the observed cosmological constant being an apt example–and so this research might be something to keep half-an-eye on.

# Still Looking

Behind it all is surely an idea so simple, so beautiful, that when we grasp it — in a decade, a century, or a millennium — we will all say to each other, how could it have been otherwise? How could we have been so stupid for so long?

-John Archibald Wheeler

# Oxford bound!

I got an acceptance letter today for my application to the Oxford D.Phil program in Theoretical physics. Yay! I haven’t got a definite supervisor or project yet, but this means that I can now worry about those details when I begin studying this October. I’ve had some contact with Pedro Ferreira and Jo Dunkley, whilst still waiting for other potential supervisors to reply to my emails…

# CMB anisotropy effects

I want to sort out the names of various effects and what-not related to the cosmic microwave background (CMB) radiation, which probably makes for boring reading material. Oh well. In particular, I’m going to summarise four *effects* that *affect *the density fluctuations in the CMB:

- The Sunyaev-Zel’dovich effect
- The Sachs-Wolfe effect
- Diffusion damping
- Baryon Acoustic Oscillation

The Sunyaev-Zel’dovich effect is when CMB photons gain a boost in energy via their inverse Compton scattering from electrons in the hot gas surrounding galaxy clusters.

The Sachs-Wolfe effect is the gravitational redshift of photons either **at** the surface of last scattering, this is called the “non-integrated Sachs-Wolfe effect”, or **not at **the surface of last scattering, in which case it is called (you guessed it) the “integrated Sachs-Wolfe effect”.

Diffusion damping is the redshifting of photons as they escape gravitational wells caused by density anisotropies in the CMB plasma. Note that this has the effect of* flattening out* density anisotropies.

Lastly, the Baryon Acoustic Oscillation (BAO) is the imprint of acoustic vibrations in the primordial plasma caused by the opposing forces of pressure and gravitational attraction. Measuring the angular peaks of the BAO tells cosmologists lots of useful information about the universe and helps us constrain cosmological parameters .

# Asymptotic safety

Something I’ve been trying to get my head around lately is ‘Asymptotic safety’. This is a reasonably in depth idea in Quantum Field Theory (QFT) but, since I’m too lazy to sit down and work through a book on QFT, I’m trying to glean the basic ideas from papers and Wikipedia. Some of the things I’ve been reading are: this and this.

So, Asymptotic safety has something to do with a QFT reaching a non-trivial fixed point in the space of physical couplings as the theory undergoes scale transformations. Apparently this implies that we can non-perturbatively renormalize a QFT, which is, of course, a good thing. Clearly I need to keep reading about this before I can explain it to someone else, so hold on for a more in-depth/better explanation.

## Firewalls

### Aside

I’ve been following the firewall debate from a layman’s spectator perspective via other physics blogs. I haven’t gotten around to reading some of the meaty details in the literature, but such papers are on the aforementioned list! I hope to read this one: http://arxiv.org/abs/1207.3123. There is at least one other paper by Susskind on the topic that I hope to read: http://arxiv.org/abs/1301.4505.

A part of this whole issue is the black-hole information paradox, which is also something that I understand only superficially. What I do know comes from Susskind’s popular science book “The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics”, which I read late last year. It’s a very gentle introduction to the concepts of entropy and information and does a good job of explaining the important concepts related to the black-hole information paradox and the ‘resolution’ proposed by complementarity. My (limited) understanding is that the firewall idea challenges some of the accepted wisdom on complementarity and general relativity’s equivalence principle. Maybe I can be less vague after carefully reading some of the literature on this stuff…