Cosmic VarianceThanks to Charles Tye!
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Well, I actually don't like too much when evil, dishonest, and hypocritical people are treated with pink gloves but Polchinski's text is a very good one despite the gloves because Polchinski clearly demonstrates that he has no problems with his shoes. ;-)
Polchinski tries to re-focus the discussion on physics. He first explains that there is no sense in which Smolin's mysterious "catastrophic predictions of a non-positive cosmological constant by string theory" could have been fully logical.
Supersymmetry breaking & vacua
Polchinski continues with evidence that well-known string theorists have always correctly judged our actual knowledge about the vacuum selection problem, both in the literature as well as in their talks. The moduli stabilization is an example where Smolin interprets a major success as a failure.
Existence of gauge theories & burden of proof
Joe explains that when someone like Smolin is making one of his bizarre statements that gauge theories don't exist, in sharp contradiction with explicit constructions (especially by Wilson), he should have an argument that goes beyond the proclamations that "they are an evil mafia", ideally a rational argument. Well, that's about 123 orders of magnitude above what Lee Smolin can offer at this moment. ;-)
In this context, Polchinski analyzes one of Smolin's hundreds of untrue theses, namely that Horowitz and Polchinski have ignored Smolin's conjectured "non-existence of gauge theory." Polchinski politely explains that Horowitz and himself have thought about it much more profoundly than Lee Smolin and all of his fans and allies combined.
Validity of AdS/CFT, rigor, and background independence
Joe repeats that it seems impossible to define Smolin's "weak form of Maldacena's duality", a nonsensical rhetorical sleight of hand that Smolin has borrowed from the creationists who divide evolution to good microevolution and bad macroevolution. ;-)
Polchinski tries to explain Smolin some basic facts about science, e.g. that scientific results are only as valid as their weakest links. Joe reviews some arguments about the temptation of rigor, especially in the context of the so-called Rehren's holography.
To show a bug in Smolin's "paradox" about causality in AdS/CFT, Polchinski mentions his paper with Nick Toumbas and Lenny Susskind. Joe emphasizes that the translation of imprecise words to precise equations is a crucial step in theoretical physics; being unable to make this step is correlated with the tendency to replace scientific arguments by sociological ones.
AdS/CFT is a major example showing that we know how to describe physics that locally looks like very diverse backgrounds - including black hole mergers, evaporation, graviton scattering, and wormholes - which invalidates Smolin's opinions that we can only describe tiny perturbations of certain fixed backgrounds and that string theory is incompatible with background independence.
Constraints vs physical Hilbert spaces
Polchinski explains that only the physical Hilbert space is physical. A larger space including non-physical states (and constraints) may be useful but it is in no way necessary. The Reference Frame has discussed this topic recently in the context of myths about quantum gravity. Smolin apparently tries to sell his confusion about the "necessary" unphysical space to be a "conventional wisdom".
Assorted technical topics: ion physics, cosmology, and unification of concepts
Joe talks about the successes with cosmology, RHIC and heavy ion physics, and warns that analogies are rarely perfect. He also explains why Smolin dislikes the AdS/CFT correspondence so much: it's because according Smolin's point of view, gauge theory is pursued by mere craftspeople while quantum gravity is studied by the real seers - and the AdS/CFT correspondence seems to be a heretical statement that the seers are equivalent to the craftspeople! ;-)
More precisely and less entertainingly, the distinction between certain concepts has really been erased, much like quantum mechanics has erased the gap between particles and waves. Those seers who don't appreciate this progress may be backward-seers but surely not forward-seers. :-)
Polchinski explains what must be done to replace the S-matrix in time-dependent backgrounds and what problems it inevitably brings.
Ultraviolet finiteness
Concerning the discussions about the UV finiteness, Polchinski settles it with another one-line proof. UV divergences always admit an IR interpretation. Zwiebach's decomposition of the moduli spaces is, according to Joe, the simplest framework to see why it is so.
Final comments about ethics
Polchinski shows why Smolin's claims about his ethical high ground are "ironic", given the poor standards of Smolin's intellectual integrity. He praises the diversity of experiences and perspectives that string theorists have and appreciates the "interdisciplinary" topics as a method to avoid excessive specialization.
