Originally an email written on July 29, 2010 :

Hello,

I’ve just finished reading Lisa Randall’s "Warped Passages (Unraveling the mysteries of the universe’s hidden dimensions)" published in 2005. Unlike some authors, she’s really recognized for her contributions to particle physics. She was said to be "the first tenured woman in the Princeton University physics department and the first tenured female theoretical physicist at MIT and Harvard University".

Her most famous Randall-Sundrum (RS) models (papers published in 1999) is unknown to me before I read her book. I’ve just checked, for example, Brian Greene in his "The Fabric of the Cosmos" only mentions this model in a footnote. To me, this book of hers has promoted her models to me. I guess these days, the brane/braneworld ideas are almost ubiquitous … but it might not be so popular before 1999.

I’ve really found this book to be (possibly the most) genuinely comprehensible to the general public as she has explained everything from the basics and she doesn’t suddenly jumped to a difficult level somewhere in her book. At times, she seems to be teaching junior school children and describes to you the main theme a couple times in somewhat different ways and even "warn" you about what you’d learn after this chapter, before she really goes into the topic. Nevertheless, her book is well-structured and she could tell you to skip a part if you don’t want to know this as it’s not necessary for the latter understanding.

Since I’ve heard/learnt about (or even worked with) the Standard Model for so many years and I’ve read quite a few of this kind of "popular" books, I’ve found only the last 1/3 is the most interesting where Randall really talks about the RS model and beyond. Nevertheless, I’ve felt that she has explained the hierarchy problem/mystery in the Standard Model very well. The RS1 model has two branes sandwiching the finite (and actually short) and warped 5th dimension solves the hierarchy problem. So, supersymmetry is not the only "elegant" way to solve the hierarchy problem. The RS2 model makes the 5th dimension infinite but still is hidden from us in the 4-dimensional space (brane). But in fact, if RS2 is to

avoid the hierarchy problem, a 2nd brane is needed but just that the 5th dimension still goes beyond the 2nd brane and the 2nd brane doesn’t end the 5th dimension. ( RS1 is just the model in their 1st paper and RS2 is the model in their 2nd paper. )

I like her joking adage that a new theory needs to go through 3 stages before being accepted: "1) it’s wrong; 2) it’s obvious; 3) it’s been done before". It sounds right to me The most benefit that I’ve gained is perhaps that after reading this book, I feel that I’m familiar (though it may be an illusion) with the extra-dimension concept. Of course, this probably builds on my learning process in the many years before … I remember that when I was a postdoc at Fermilab (~1997-2000), my colleagues have analyzed our data to see whether there was any trace of extra-dimension. Extra-dimension in string theory has been there for a long time but RS probably has shown the usefulness of extra-dimension outside the string theory.

At the end, she also has given a good account of the duality with quite a few practical examples. But her last comment that the duality (like 10-dimension superstring being dual/equivalent to 11-dimension supergravity) has blurred the definition of dimension is something that I haven’t heard people talk about. … Hmm … there is a point …

There are a couple topics in her book that I might be even be more familiar with than she is. I may be able to tell a bit better story about the precision measurements of the beam energies of LEP and the tidal corrections … and probably also about the Tevatron experiments at Fermilab …

I think typically, experimentalists have used missing energy in detectors to search for the evidence of extra-dimension. But her explaining the abundance of Kaluza-Klein particles if they’re around the 1 TeV scale will give more interesting and prominent evidence.

I like this book. It’s a long read (500 pages including everything) but towards the end, it’s worth it. I can highly recommend it to you if you’re curious about particle physics and physics in general. She doesn’t seem to be a string theorist but she’s not hostile to the string theory and seems to even work with the string theorists …. She calls herself model-builder (from bottom-up), different from the string theorists (from top to bottom).

Kin

PS: Just in case, you don’t need to rush to read it now …maybe after your summer internship … Hahaha ….

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