Post a Comment On: Backreaction

[Image]The Universe in the Rearview Mirror: How Hidden Symmetries Shape Reality
By Dave Goldberg
Dutton Adult (July 11, 2013)

In his new book “The Universe in the Rearview Mirror,” Dave Goldberg expounds the important role of symmetries in the fundamental laws of physics. He starts with the discrete operations of charge-conjugation, parity, and time inversion, and their combinations. After introducing the reader to Emmy Noether and her work, he discusses continuous symmetries, homogeneity and isotropy, as well as Lorentz-invariance before continuing with gravity. The later chapters deal with gauge symmetries and symmetry breaking. The book finishes with existing proposals for physics beyond the standard model, grand unification, supersymmetry, and the missing theory of quantum gravity.

Goldberg does a remarkably good job conveying a very technical topic in non-technical terms and with only a handful of equations (yes, E=mc2 among them). He works mostly with analogies and writes in an engagingly colloquial way with a large dose of humor, though some readers might find the high density of jokes more distracting than helpful*. The bibliography and the guide to further reading provide helpful references for the readers who wish more details, and the book also has a brief glossary.

Symmetries that “shape reality,” as the subtitle of the book says, are a vast topic of course. Goldberg has focused on these symmetries that (for all we know) shape reality on the most basic level. He does not (except for the purpose of a brief analogy) touch upon the much broader topic of emergent symmetry and order in condensed matter systems, or in other areas of physics and science more generally. This focus has the benefit that the book is relatively lean (291 pages, hardcover) and maintains its momentum, but the blurb could have been more descriptive.

On the downside, the book is confusingly structured and the reader who doesn’t bring prior knowledge might become frustrated in several places. For example the WMAP mission is mentioned in the first chapter, without explanation for what exactly it measures and without an image. The radiation of the cosmic microwave background is again introduced in the third chapter, without referral to the earlier mentioning of WMAP, and temperature anisotropies are briefly mentioned here. Temperature anisotropies are then again introduced at the end of this chapter and here the WMAP image finally appears (low-resolution black-white), alas without the image being mentioned in the text and without explanation for what it shows.

In fact, while the graphics that have specifically been produced to accompany the text are well done and helpful, the book also contains a number of images that are useless and only loosely connected to the text. An image on page 41 I guess shows the Venus transit which is mentioned in the text on this page, or maybe it shows an exercise to find one’s blind spot. On page 109, the reader encounters a Klein bottle and the only reason I can infer is that the next page mentions Emmy Noether “took classes with Hilbert and Klein.” An image on page 118 (no caption) shows Einstein arcs and the explanation in the text amounts to “massive bodies bend light”. The image on page 250 remained a mystery to me until I found it in the Wikipedia entry to “Sisyphus” (mentioned on that page).

The book is also confusing and unstructured in other ways. Goldberg begins to talks about “the elusive dark matter particle” (in itself a questionable phrase) in Chapter 9 without so much as mentioning what dark matter is or what evidence we have for it. He uses the Planck length in chapter 6, but only explains it in Chapter 10. The cosmological constant problem is introduced twice. The elaboration on the twin paradox somehow misses to spell out what the resolution of the paradox is. It is mentioned that inflation was proposed “to get around the horizon problem” but the reader is not actually told how inflation solves the problem. Evidence for inflation amounts to “we’re reasonably certain that it is [correct]”. Goldberg elaborates on the multiverse and later on the compactified dimensions of M-theory, but does not connect the two topics. He speaks about the entropy of matter in the early universe before explaining what happened in the early universe. On page 167/168, I came across the possibly most opaque motivation for quantum gravity that I’ve ever encountered. Luckily there is a considerably better one on page 269. A quotation from Stephen Hawking expressing the opinion that information is not lost in black holes is dumped onto the reader in a description of black holes as “entropy-producing machines” without so much as mentioning the black hole information problem.

I’ll not go down the full list of similar notes that I took while reading; you get the picture.

Goldberg has to be credited for making his text timely by referring to very recent works, for example he mentions Verlinde’s contribution on entropic gravity. This reference (the only reference on the topic) appears in a section on the arrow of time and at least I could not infer the direct connection, besides both having something to do with entropy. Goldberg uses Max Tegmark’s proposed level structure of the multiverse and in the last chapter on physics beyond the standard model we meet Garrett Lisi the surfer without university affiliation who allegedly stunned everybody with proposing his theory of everything. It somehow goes unmentioned that Lisi has PhD in physics. I’m picking at this point not because I don’t think the E8 root diagram is pretty, but because the reader is left with the unfortunate impression that surfing is all you need to understand modern physics. Towards the end of the book the reader can find a very good summary of the recent discovery of the Higgs particle and its relevance.

In summary, the book is valuable for the selection of topics and for conveying the relevance of symmetries in the laws of nature, but the execution leaves wanting. Sean Carroll’s two books for example cover a substantial part of the physics built upon Goldberg’s hidden symmetries, but the reader who does not bring prior knowledge about modern physics will learn a great deal more from Carroll’s more didactic approach. Goldberg however succeeds in inspiring a sense of awe for the power of symmetries, not at least because awesome seems to be one of his favorite words.
*Humor, of course, is always a matter of taste. So let me just say that messages like “science nerds… spend … many nights alone” or physicists don’t know how to dress elegantly and don’t get invited to dinner parties, strike me more as funny-peculiar than funny-ha-ha.