Thursday, December 15, 2005

Susskind's Sophie's Choice

Susskind’s new book The Cosmic Landscape: String Theory and the Illusion of Intelligent Design is generating a lot of interest. Recently he gave a fascinating interview to Amanda Gefter at NewScientist.

I especially enjoyed the last question and answer:
If we do not accept the landscape idea are we stuck with intelligent design?

I doubt that physicists will see it that way. If, for some unforeseen reason, the landscape turns out to be inconsistent - maybe for mathematical reasons, or because it disagrees with observation - I am pretty sure that physicists will go on searching for natural explanations of the world. But I have to say that if that happens, as things stand now we will be in a very awkward position. Without any explanation of nature's fine-tunings we will be hard pressed to answer the ID critics. One might argue that the hope that a mathematically unique solution will emerge is as faith-based as ID.
The landscape to which he refers is an estimated 10500 environments consisting of different values for the physical constants, i.e., different laws of physics. At the risk of oversimplifying, possible universes exist as local minima in this vast megaverse. Our universe is one with the “just right” fine-tuning that we observe.

Susskind’s answer shows that his book should be subtitled String Theory and the Possible Illusion of Intelligent Design. He has done nothing whatsoever to disprove fine-tuning. Nothing. He has only countered it with a religious speculation in scientific language, a God of the Landscape. Snatching victory from the jaws of defeat, he tells us that we should embrace the String Theory landscape, not in spite of its ugliness, but rather because of it. Physics should change its paradigm and sing praises to inelegance. Out with Occam’s razor, in with Rube Goldberg. Out with reductionism, in with lots of free parameters. Why? Because if we don’t (according to Suskind) there really is no way to explain the fine-tuning, except by Intelligent Design. He even likens, in his last sentence quoted above, those physicists who search for the antithesis of his landscape, a simple, beautiful fundamental theory, to IDers.

I think he is correct. For a fundamental theory that predicted all the constants would be a “win” for ID—it would destroy the only real threat to cosmological ID: multiple universes with varying laws of physics.

The subtext (at times explicit) in Susskind’s book is that fine-tuning is real, in the sense that our universe really does exist on a knife’s edge, so much so that it demands attention. The only possible way that it is an illusion is if our universe is but one of many. To save materialism, Susskind argues that we must explain this fine-tuning, and his landscape has the best chance of playing the role of a white knight.

What about falsifiability, that inconvenient scientific requirement that critics like to bring up when discussing ID? How does Susskind answer attacks on the landscape’s falsifiablity? Well, he suggests that maybe, though not likely, the one landscape prediction: a negative curvature to the universe, might be detected through more precise measurements of the cosmic background. Presently, our universe appears to be flat, corresponding to a value of the total density Ω0 equal to 1. In his review of Susskind’s book, cosmologist George Ellis looks at the possibility:
The particular multiverse version proposed by Susskind, however, has the great virtue of being testable in one respect. It is supposed to have started out by quantum tunnelling, resulting in a spatially homogenous and isotropic universe with negative spatial curvature, and hence with a total density parameter Ω0<1. The best observationally determined value for this parameter, taking all the data into account, is Ω0=1.02+/-0.02. Taken at face value, this seems to contradict the proposed theory. But given the statistical uncertainties, the observations do not definitively exclude Ω0<1, so the theory survives; nevertheless, the observed value should be taken seriously in this era of 'precision cosmology'. These data are not discussed in the book — a symptom of some present-day cosmology, where faith in theory tends to trump evidence. Presumably the hope is that this observational result will go away as more evidence is collected. (Nature 438, 739-740, 8 December 2005)
Ouch. (It should also be noted that a detection of a slight negative curvature would be consistent with the landscape, but it wouldn’t prove it.)

Susskind seems to recognize that falsifiability is a weakness in his theory, so (you just have to give him credit for moxie) he simply goes right to the source. In the same NewScientist interview, he states:
There is a philosophical objection called Popperism that people raise against the landscape idea. Popperism [after the philosopher Karl Popper] is the assertion that a scientific hypothesis has to be falsifiable, otherwise it's just metaphysics. Other worlds, alternative universes, things we can't see because they are beyond horizons, are in principle unfalsifiable and therefore metaphysical - that's the objection. But the belief that the universe beyond our causal horizon is homogeneous is just as speculative and just as susceptible to the Popperazzi.
In other words—the routine assumption that the part of the universe that we cannot see is the same (has the same physical laws) as what we do see is just as unfalsifiable. Chutzpah!

Susskind has presented the physics community with what is, for some (not this writer), a Sophie's Choice: a hidious, complictated, unfalsifiable String-Theory Landscape, or Intelligent Design.

Susskind rocks.

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