A write-up by John Schwarz of his Erice lectures from this past summer has now appeared on the arXiv, with the title Status of Superstring and M-theory. In his second lecture, Schwarz provides a good review of the various attempts to do “string phenomenology” by trying to find a “string background” that doesn’t conflict with known particle physics. He devotes particular attention to the newest of these backgrounds, so-called “F-theory local models”, providing a summary of the rather complicated constructions involved. Schwarz doesn’t describe any experimental predictions of such models, just noting:
It will be very interesting to see what predictions can be made before the experimental results pour in and whether they turn out to be correct.
For more discussion of these models and the question of whether they predict anything, see here.
Schwarz begins with an account of his interactions with Sidney Coleman at Aspen and elsewhere:
I recall him once saying that there are three things that he does not like, all of which are becoming popular: supersymmetry, strings, and extra dimensions. Obviously, my views are quite different, but this did not lessen my regard for him, nor did it harm our personal relationship. In fact, I respected his honesty, especially as he did not try to impose his prejudices on the community.
About the anthropic landscape issue, he has this to say:
Perhaps the absurdly large number of flux vacua that typically arise in flux compactifications has discouraged people from trying to construct viable particle physics models. In fact, this large number of vacua has motivated the suggestion that various parameters of Nature (such as the cosmological constant) should be studied statistically on the landscape. I don’t really understand the logic of doing this, since this approach seems to assume implicitly that Nature corresponds to a more or less random vacuum. This in turn is motivated by some vague idea about how Universes are spawned in the Multiverse in a process of eternal inflation. Then the story gets even more entangled when the anthropic principle is brought into the discussion. Some people are enthusiastic about this approach, but I find it fundamentally defeatist. It is not the way I like to think about particle physics.
Meanwhile, public promotion of the Multiverse continues, with the opinion pages of Britain’s The Independent today featuring a piece by Bernard Carr entitled Fifth dimensions, space bubbles and other facets of the multiverse. Carr describes the “growing popularity” of the multiverse proposal, ending with:
But is the “multiverse” a proper scientific proposal or just philosophy? Despite the growing popularity of the proposal, the idea is speculative and currently untestable – and it may always remain so. Astronomers may never be able to observe the other universes with their telescopes and particle physicists may never be able to detect the extra dimensions with their accelerators. So, although some physicists favour the multiverse because it may do away with the need for a creator, others regard the idea as equally metaphysical. What is really at stake is the nature of science itself.
Carr characterizes some multiverse proponents as atheists favoring something that doesn’t seem to fit into the conventional scientific method because it gives an answer to the argument from design for a deity. For more about this all-too-common argument for the multiverse, being promoted by Susskind and others, see here. In answer to such claims about religion being promoted by physicists, New Scientist this week is running a sensible piece by Amanda Gefter entitled Why it’s not as simple as God vs the multiverse. It makes the obvious point about the multiverse-God dichotomy:
Science never boils down to a choice between two alternative explanations. It is always plausible that both are wrong and a third or fourth or fifth will turn out to be correct.
Update: For more multiverse mania, see today’s colloquium at Perimeter here. The intense promotion of this pseudo-science continues, but I don’t think it’s getting any traction.
Update: Yet more media attention to the God vs. Multiverse debate, now from the Guardian.