Warped Passages
I finally got around to reading Lisa Randall's Warped Passages: Unraveling the Mysteries of the Universe's Hidden Dimensions. Writing a popular book on advanced physics seems like kind of an unlikely enterprise, on the face of it. It's pretty well extablished that it takes six or eight years of hard post high school study for highly motivated and mathematically talented students to get a sound technical understanding of frontier science, so isn't it pretty absurd to expect to explain the same to people who never learned or promptly forgot the elements of algebra and calculus?
Remarkably enough, many physicists have attempted, and often succeeded in just that daunting task. I guess my favorites among those I know would be Steven Weinberg's The First Three Minutes, Kip Thorne's Black Holes and Time Warps, and Brian Greene's The Elegant Universe. Randall's book is in many ways a worthy successor to these. I don't find her quite as elegant a stylist as Weinberg or Greene, and she doesn't have Thorne's knack for the telling anecdote, but she is tackling what looks to me to be an even more difficult task - explaining branes and their potential relevance to leading problems in particle physics.
Because she has to explain not only the standard model of particle physics but also at least one of its diseases, the hierarchy problem, she sets herself a tougher task than the three authors I mentioned. Since she doesn't use mathematics (except for a few occasionaly useful math endnotes), she is forced to rely heavily on analogies, which she does with a vengence. Of course I had a high fever while reading much of the book, but a lot of the analogies left my head hurting. One that still haunts me is her explanation of color antiscreening in terms of office gossip.
I liked her explanation of the hierarchy problem though, and I liked her explanation of how extradimensional branes might help. Several of the later chapters are devoted to the idea of how a single extra (fifth) dimension might confine gravity if it was an anti-deSitter warped dimension (negative curvature in only the fifth dimension with sections perpendicular to the fifth dimension all being flat).
After a few of these had been exhibited, I started getting impatient. So, what are you telling me here, are these just some subset of infinitely many possible weird worlds or what. Also, at this point the water sprinkler and ducks on a pond gravity analogies started driving me nuts.
The last several chapters had some interesting tidbits. The major theme here was the possible ambiguity of the notion of dimension itself. A few quotes on various notions: From Chapter 24 p. 450 on AdS and duality. Dualities of theories with different numbers of dimensions.
On T-Duality p. 451
She lines up a lot of big guns to agree that something funky is happening at very small scales.
Ed Witten: space and time may be doomed.
Nathan Seiberg: I am almost certain that space and time are illusions.
David Gross: Very likely, space and perhaps even time have constituents; space and time could turn out to be emergent properties of a very different looking theory.
Lisa Randall adds:
This seems a bit too coy. Perhaps the influence of her faithful reader and critic Prof Motl disuaded her from mentioning what many physicists from Heisenberg (at least) on have believed: that space and time, like matter and energy, have an underlying granular structure.
Alain Connes and Carlo Rovelli, for example, think they have some ideas about that.
Branes in extra dimensions and warped branes.
Remarkably enough, many physicists have attempted, and often succeeded in just that daunting task. I guess my favorites among those I know would be Steven Weinberg's The First Three Minutes, Kip Thorne's Black Holes and Time Warps, and Brian Greene's The Elegant Universe. Randall's book is in many ways a worthy successor to these. I don't find her quite as elegant a stylist as Weinberg or Greene, and she doesn't have Thorne's knack for the telling anecdote, but she is tackling what looks to me to be an even more difficult task - explaining branes and their potential relevance to leading problems in particle physics.
Because she has to explain not only the standard model of particle physics but also at least one of its diseases, the hierarchy problem, she sets herself a tougher task than the three authors I mentioned. Since she doesn't use mathematics (except for a few occasionaly useful math endnotes), she is forced to rely heavily on analogies, which she does with a vengence. Of course I had a high fever while reading much of the book, but a lot of the analogies left my head hurting. One that still haunts me is her explanation of color antiscreening in terms of office gossip.
I liked her explanation of the hierarchy problem though, and I liked her explanation of how extradimensional branes might help. Several of the later chapters are devoted to the idea of how a single extra (fifth) dimension might confine gravity if it was an anti-deSitter warped dimension (negative curvature in only the fifth dimension with sections perpendicular to the fifth dimension all being flat).
After a few of these had been exhibited, I started getting impatient. So, what are you telling me here, are these just some subset of infinitely many possible weird worlds or what. Also, at this point the water sprinkler and ducks on a pond gravity analogies started driving me nuts.
The high probability for the graviton to be found near the Gravitybrane, and the corresponding concentration of the gravitational field there, might also be compared to the high likelihood of greedy ducks in a pond being near the shore.I hope that helps somebody. Headpain ouch!
The last several chapters had some interesting tidbits. The major theme here was the possible ambiguity of the notion of dimension itself. A few quotes on various notions: From Chapter 24 p. 450 on AdS and duality. Dualities of theories with different numbers of dimensions.
We know that the number of dimensions should be the number of quantities you need to specify the location of an object. But are we always sure we know which quantities to count.
On T-Duality p. 451
…an infinite dimension in one theory is T-dual to a theory with one dimension fewer (since a zero size circle doesn’t count as a dimension)...
Once again the meaning of dimension is ambiguous.
One of the strongest reasons for believing that our spacetime description is inadequate at the Planck scale length is that we don’t know any way, even in theory, to examine such a short distance.
Facts so bizarre cry out for a deeper explanation.
She lines up a lot of big guns to agree that something funky is happening at very small scales.
Ed Witten: space and time may be doomed.
Nathan Seiberg: I am almost certain that space and time are illusions.
David Gross: Very likely, space and perhaps even time have constituents; space and time could turn out to be emergent properties of a very different looking theory.
Lisa Randall adds:
Unfortunately, no one yet has any idea what this more fundamental description of space and time will turn out to be.
This seems a bit too coy. Perhaps the influence of her faithful reader and critic Prof Motl disuaded her from mentioning what many physicists from Heisenberg (at least) on have believed: that space and time, like matter and energy, have an underlying granular structure.
Alain Connes and Carlo Rovelli, for example, think they have some ideas about that.
Branes in extra dimensions and warped branes.
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