MisAnthropic Me
If you are not a string theorist but nonetheless occasionally cruise string or anti-string blogs, you have probably heard a lot of talk about “the landscape.” Steven Weinberg has the text of a talk called “Living in the Multiverse" (hep-th/0511037) out, and he talks about the landscape, the multiverse, anthropic reasoning, and what it all means. Right up front he has a nice description of how the landscape arises:
The problem this presents is that it means that there are about a kazillion (somewhere between 10^100 and 10^500, say) possible solutions, each, presumably, corresponding to a potentially very different universe. The path that Weinberg hopes might lead us out of this is the so-called Anthropic Principle. The idea is that we can hope to deduce something from the fact that our universe turned out to be habitable, so far. It also means giving up any hope of, say, deriving the masses of the elementary particles and the strengths of their interactions from fundamental principles. It’s not clear to me why it doesn’t include giving up any hope of predictivity at all.
A lot of physicists hate this idea, as do I, but that doesn’t mean it isn’t right. It might have been Max Born who liked to remind Einstein that God might not have designed the universe the way Einstein would have liked him to have.
Lubos Motl has a post on the talk here.
Now we may be at a new turning point, a radical change in what we accept as a legitimate foundation for a physical theory. The current excitement is is of course a consequence of the discovery of a vast number of solutions of string theory, beginning in 2000 with the work of Bousso and Polchinski.1 The compactified six dimensions in Type II string theories typically have a large number (tens or hundreds) of topological fixtures (3-cycles), each of which can be threaded by a variety of fluxes. The logarithm of the number of allowed sets of values of these fluxes is proportional to the number of topological fixtures. Further, for each set of fluxes one obtains a different effective field theory for the modular parameters that describe the compactified 6-manifold, and for each effective field theory the number of local minima of the potential for these parameters is again proportional to the number of topological fixtures. Each local minimum corresponds to the vacuum of a possible stable or metastable universe.
The problem this presents is that it means that there are about a kazillion (somewhere between 10^100 and 10^500, say) possible solutions, each, presumably, corresponding to a potentially very different universe. The path that Weinberg hopes might lead us out of this is the so-called Anthropic Principle. The idea is that we can hope to deduce something from the fact that our universe turned out to be habitable, so far. It also means giving up any hope of, say, deriving the masses of the elementary particles and the strengths of their interactions from fundamental principles. It’s not clear to me why it doesn’t include giving up any hope of predictivity at all.
A lot of physicists hate this idea, as do I, but that doesn’t mean it isn’t right. It might have been Max Born who liked to remind Einstein that God might not have designed the universe the way Einstein would have liked him to have.
Lubos Motl has a post on the talk here.
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