Tuesday, July 5, 2011

Jim Baggott's "The Quantum Story"

This is a fairly exhaustive tour of the history of quantum physics. I appreciated the older bits more than the newer bits. That story has been honed by retelling many times and Baggott does a workmanlike job of retelling it once more. But the twenty chapters on the bits that happened over the last 40 years are much more difficult to enjoy. They are more like a forced march through enemy territory than a stroll through the great story of scientific advance.

I'm willing to admit that more recent science is more complex, more textured, more mathematical, etc. But if you are going to write something for the general reader and not a textbook for academics, you need to work harder to polish the story. Baggott needs to bring out clearer themes. He needs to make his analogies more memorable. He needs to give the reader a better sense of understanding "the unfolding story" and the struggle of the lead actors in the drama. Baggott does toss in some humourous asides but there is not nearly enough focus on "the story", i.e. something memorable that will let the non-insider close the book feeling a sense deep understanding. Instead I come away with an appreciation of complexity and details and false steps and hordes of co-workers making tentative progress. There's nothing satisfying there. If I want to put this book under my arm and go brag about how I "now understand quantum physics" this isn't the book I would feel prepared me for that task.

I appreciate the difficulty of the task that Baggott laid for himself. I feel he has done herculean work in understanding the science. But he hasn't brought the tablets down from the mountaintop. I keep thinking of authors the past who achieved this almost magical goal of making me feel I understood the cutting edge of science. They have a knack of finding a way to cut through the complexity and come up with techniques to get at "the essence" of the science. Sure, I know that nobody can read one book and be an "expert". Worse, in any real science today, you must spend years to master the mathematics since the math is in effect the science. But the authors I admire can draw word pictures that leave the general reader well satisfied that they have "caught the essence" of the subject matter knowing full well that a real understanding takes many, many years of serious study.

I appreciate authors like Baggott trying to bring the mountain to Mohammad. Sadly in this case I got a lot of rock and landfill dumped in my backyard. I didn't get a mountain. (Translation: I don't literally want the mountain. I want a "poetic" sense of having ascended the mountaintop. I want the "experience" without the gritty reality of all that rock and soil and laborious rock scaling and technical "climbing".)

Here's a selection from the book to give you a taste of Baggott's style:
There remained the puzzle of strings vibrating in a ten-dimensional space-time. To a certain extent, the idea of spatial dimensions additional to the familiar right-left, backwards-forwards up-down dimensions had been anticipated by German mathematician Theodor Kaluza in 1919. He sent Einstein a draft paper showing how the two forces then known -- electromagnetism and gravity -- could be unified in a single theoretical framework which required four spatial dimensions. In 1926, Oscar Klein had suggested that the extra dimension might be rolled up so small and tight, with a radius equal to the Planck length, that it would remain forever inscrutable. The resulting framework became known as Kaluza-Klein theory.

But why stop at one hidden dimension? If there could be one such dimension, why couldn't there be two, or three, or nine? The point about superstring theory was that it demanded precisely nine spatial dimensions for the strings to vibrate in, no more and no less. It was necessary to assume that the six additional spaces are curled up in a small bundle so that we can't experience them. Superstring theory had something to say about the shape of these extra dimensions, but it had nothing to say about their size.

In 1985, Princeton physicists Philip Candelas, Gary Horowitz, Andrew Stominger, and Witten published a paper explaining that the topology of the six extra dimensions had already been found as the solution to an abstract problem in mathematics by Eugenio Calabi in 1957 and Shing-tun Yau in 1978. According to this theory, at every point in our familiar three-space, there lies a six-dimensional Calabi-Yau shape, so small that it is beyond the reach of experimental instruments.

Each 'hole' in the Calabi-Yau shape gives rise to a family of low-energy string vibrations. A Calabi-Yau shape would therefore produce three families of vibrational patterns, corresponding to the three generations of particles in the Standard Model.

But this was not plain sailing. Although the theory demands that the extra dimensions curl up into a Calabi-Yau shape, there are potentially hundreds of thousands of such shapes that would satisfy this requirement. Each candidate comes with its own set of free constants which determine its size and shape. Each produces a different version of particle physics.

These were not the only problems. The low-energy vibrational patterns correspond to massless particles, yet the three generations of particles of the Standard Model all have mass. The theory also predicts many more vibrational patterns than there are particles.

Despite the great rush of enthusiasm, it was clear that supersting theory was quickly losing any sense of uniqueness and hence a capacity to make unique predictions. It would have some way to go before it could fulfil its early promise as the theory of everything.
The above shows you that Baggott certainly loads up with prose with lots of details, but as you read through it you wonder "where is all this leading?" and "what am I supposed to remember from this" and "what does all this mean?" Notice he slips 'holes' in Calabi-Yau spaces past you without giving you an idea of what a Calabi-Yau space "looks like" and how you would find a 'hole' in one. It sounds like you've learned something fascinating: 'holes' give rise to low-energy string vibrations. But what does that mean? Notice all the researchers referenced. Details, but why?

I'm not saying "don't read this book". I read it. I found it interesting. But I was left wishing for a better telling of the tale. Even as I sit a few hours after finishing this book I feel the details dissolving away. I have only a tenuous grasp on the 100 year history that Baggott has so painstakingly written with details and names. I fear that in a month almost all will be gone because there was not enough "glue", not enough "story line", not enough "what does it mean?" explained as the text plows through so much history.

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