First of all, it is a very insightful and extremely useful book by Lisa Randall
Warped Passages : Unraveling the Mysteries of the Universe's Hidden Dimensions
by Lisa Randall
Be sure that I will write much more about this book as the date of publishing is getting closer. Yes, I've read this book, and it certainly deserves your attention! On the other hand, I have not seen Lenny's book
An Introduction To Black Holes, Information And The String Theory Revolution: The Holographic Universe
by Leonard Susskind
Well, Lenny Susskind is a character, and it is very natural that he writes a book about all these wonderful ideas - many of them are his ideas. But I can't tell you anything about the book.
The information about these books scared Peter Woit - because every time the public learns more about particle physics and string theory, Peter Woit's struggle to kill string theory becomes more hopeless. And therefore Peter wrote an article "More hype on its way" on his blog "Not even wrong":
http://www.math.columbia.edu/ ... 000109.html
The section with comments was pretty illuminating because we could learn that it is not just string theory and the anthropic principle that Peter Woit hates. He also informed us that he does not like
- The research of the hierarchy problem. In his opinion, it is enough to believe that there is no grand unification, and therefore there is no GUT scale, and therefore we don't have to worry about the hierarchy problem - it does not really exist.
- You might think that I am twisting and trying to humiliate Peter, and he could not write something like that, but you can check yourself! Just to be sure, unless we postulate very new physics, such as large or warped extra dimensions, quantum corrections to gravity only become important at the Planck scale about 10^{19} GeV - which can be calculated without any assumptions of grand unification. If we want to claim that there is any field-theoretical description at energies below the Planck scale, we must explain the parameters, including the obvious gap between the electroweak scale and the Planck scale, a gap that is vulnerable to quantum corrections in the Standard Model.
- Extra dimensions. Obviously, Peter states that the ideas related to extra dimensions are even more ridiculous than string theory itself, and this is not anything new.
- But we also learned some time ago that he is totally unimpressed by gauge coupling unification - and of course by the very idea of supersymmetry.
That's a good place to say a couple of words about these cultural differences.
In the 1980s, the gap between the theorists and phenomenologists - or, alternatively, between the top-bottom and bottom-up approaches - was huge. String theory and conventional particle physics were two different cultures, and this also affected the separation to two arXivs in the early 1990s.
There has been at least one revolution - the second superstring revolution - in the stringy camp, but virtually no progress in the non-stringy camp. That's one of the reasons that brought these two camps much closer to each other. The other reason is less pragmatic and more important scientifically: namely the specific new discoveries.
In phenomenology, the large and warped extra dimensions were proposed as the new ways to solve the hierarchy problem. These approaches are clearly rooted in string theory; without the influence of string theory, it would seem unlikely that any approach based on extra dimensions would be studied seriously.
The case of extra dimensions in phenomenology was not the first example in which string theory gave bottom-up model builders new ideas and mantinels to probe possible new physics beyond the Standard Model - supersymmetry was another example - and most phenomenologists started to realize that there there is something about string theory if it's able to generate viable paradigms for their own field.
Of course, many phenomenologists don't care about the rest of string theory, besides these stringy-inspired ideas, and it's their legitimate attitude. On the other hand, it is conceivable that the future will show them that they should have taken many more details from string theory than just these general ideas such as extra dimensions and braneworlds. Well, in reality, many phenomenologists are trying to apply other ideas from string theory, too.
The concepts of holography and the AdS/CFT correspondence were very important for convergence of the phenomenological and stringy communities, too. The renormalization group flow looks like an extra dimension - the holographic dimension whose existence seems to be a general feature of quantum gravity. Most string theorists were trained as quantum field theorists anyway, and therefore it is not too surprising that the two communities overlap significantly in their investigation of holography - in the context of Randall-Sundrum models or the AdS/CFT correspondence.
The stringy and particle camps are still working independently most of the time, but there is a significant amount of interactions. Harvard is one of the places where the interactions are very strong, and I was explained that the gap between these two cultures is slightly bigger at some places in California, for example.
One may also consider a third culture, namely loop quantum gravity. From the Harvard perspective, the gap between the hep-** cultures on one side, and loop quantum gravity on the other side is virtually infinite. There is a wide consensus between all visible parties at Harvard - string theorists as well as particle physicists - that the precise proposals of the loop quantum gravity to modify the rules of physics (and to ignore the lessons of quantum field theory) is simply rubbish.
That's Harvard, but the people from the Perimeter Institute can tell you stories about their peaceful co-existence with the loop quantum gravity people over there. Of course, it is extremely hard for me to imagine how the string theorists can live so happily with so much anti-physical nonsense around, but it's probably just a matter of mutual brain-washing.
