Tuesday, February 07, 2006

Book / Warped Passages by Lisa Randall

Last year Harvard President Larry Summers ignited a firestorm when he suggested there might be innate reasons why women were underrepresented in the upper ranks of hard science and math. Presumably Lisa Randall of the Harvard Physics Dept. is the exception, since her papers on theoretical physics have been cited 1,000s of times.

I will not try to summarize this book, which would take too long. I found the first 1/3 to 1/2 rather tedious and sub-par, because she covers a lot of ground that will be familiar to readers of other popular physics books, without adding anything new or doing an especially good job. I found her analogies nebulous, despite having somewhat of a woman's touch. Fortunately it gets much better later on, when she talks about her own work, how it fits in, and where it may lead.

After a refreshing denunciation of string theory, in which she explains how they are all stuck in a tree (with a top down approach) and there is no reason to believe they will ever get anywhere, she outlines her "model building" approach, which is to try and develop notions of how extra dimensions might work, possibly including the concept of branes (which overlap with string theory), and how they can be used to model the "next phase" of particle physics, including predictions that might be testable in the forthcoming Large Hadron Collider (LHC). These are reasonably cool ideas, and it looks like she may be onto something.

The goals of a credible model, we infer, are to (1) reproduce the "Standard Model" of particle physics (quarks and such), (2) not violate cosmology, and (3) shed some light on major riddles, notably the "hierarchy problem," or why is gravity so weak compared to the other three forces, and the Planck Mass so huge? She postulates an extra dimension, or several variations thereof, into which gravity can heavily leak away, while everything else looks the same. The concept of supersymmetry, which has never been proven, is jettisoned.

Useful ideas I got from this book relate to how extra-dimensional objects would look. If you lived in a 2-dimensional "Flatland" and a 3-dimensional sphere passed through your plane, it would look like a circle that expands, contracts, and then disappears. Likewise if a 4-sphere passes through our 3-brane, it will look like a sphere that expands and contracts. Extra-dimensional particles, if we can create them, will "appear" as missing mass/energy in particle traces. A stationary object with momentum in another dimension (even a rolled up one) will seem heavier, and its motion along another dimension (an extended or infinite one) could be modeled as color change.

Randall criticizes the excessive faith in string theory, which has led some universities such as Princeton to focus solely on string theory, to the exclusion of her preferred "model building" at energy levels that have some hope of being tested. However, she makes no reference to loop quantum gravity (LQG). This book is basically a vanity piece to publicize her predictions prior to the LHC coming on stream. Still she should have at least mentioned LQG, which offers a competing theory of gravity with plenty of substance, and not doing so seems cowardly to me.

Net-net: This popular book provides an overview of a "model building" approach to physics (at soon-to-be-achieved energy levels) that is neither string theory nor LQG, and hence is recommended (as an antidote to both of them) for those interested in expanding their views of modern physics.

(See also my related posting on the perils of "Micro Black Holes," based on a quote from this book.)

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