String Theory = Intelligent Design?

(This article was originally posted on blogger.com on Oct 27, 2005)

Don’t get me wrong. I don’t think – as Peter Woit seems to be doing – that the scientific status of string theory is in any way comparable to that of the crazy set of ideas called “Intelligent Design”. Basically, Intelligent Design (ID) purports to ‘explain’ the complicated structures seen in life – as the DNA, the structure of a human eye, blood clotting, the immune system etc. by introducing a ‘designer’ (God, aliens, or whatever) clever enough to yield the blueprint of life in all its forms. But in reality, ID does not explain anything at all.

Commenting on Lawrence Krauss’ new book on extra dimensions, Peter Woit says:

The behavior of string theorists that Krauss identifies as most like religion is the argument that “the theory is so beautiful it must be true.” I actually don’t hear many string theorists making this argument these days. If the theory actually were beautiful in the sense of providing some impressive new understanding of physics in terms of some simple, compelling mathematical or physical idea, that actually would be a good reason for believing in it, although not a completely conclusive one. All attempts so far to connect the theory to real physics lead to hideously complicated and ugly constructions.

and,

Some string theorists such as Susskind, argue that one should believe in string theory anyway, and it is this argument which seems to me to be more like religion than science. It’s my impression that Susskind and others are believing something for sociological and psychological reasons, something for which they have no rational, scientific argument. This behavior is not distinguishable from that of many of the intelligent designers, and if it becomes more widespread it ultimately threatens to do real damage to the public perception of science in general and theoretical physics in particular.

Peter’s main argument for comparing string theory with ID is, that

[…] if after a lot of work, there still is no indication that an idea can produce predictions, the continued pursuit of it at some point stops becoming science and starts becoming something more like religion. Susskind and other anthropic landscapeologists have already gone past this point: they have no plausible idea about how to ever get real predictions out of their framework. String theorists who argue that the theory is still too poorly understood, that more work is needed to understand whether there is some way around the radical non-predictivity implied by the landscape, are nominally still doing science.

There are some obvious reasons for which ID is not in any way a scientific theory:

it can in principle not be falsified

it violates Occam’s razor

it is rumored to be supported by a (completely flawed) understanding of the chance of a biological structure like an eye to appear as a result of evolution (typically estimated to be 1 in 10^{150} or less – even though such a ‘calculation’ does not make any sense)

it makes no real predictions for any biological systems

it is like saying, that science should stop trying to find explanations for things, since supporters of ID argue, that everything which as of yet is not explained by evolution must by explained by an ‘intelligent designer’

In comparison, string theory is completely different; some of the reasons are, I think, that in string theory:

the appearance of gravity is inevitable

all interactions are unified

there are no adjustable dimensionless parameters

gauge invariance, supersymmetry and higher dimensions comes out in a very natural way (and moreover, the number of dimensions is not something which is assumed, but something which is determined by mathematics)

the extra dimensions can be ‘large’ (like in the Randall-Sundrum models) and the existence of those dimensions can be tested, for example at the LHC

the Standard Model can be reproduced in a very simple way (for example by intersections of D6-branes wrapping a T^6, or by D3-branes placed at an orbifold singularity – though symmetry breaking remains to be worked out)

the ‘hierarchy problem’ can be solved by the existence of extra large dimensions (Randall-Sundrum)

the entropy of certain classes of black holes can be accounted for (for example in terms of coincident D1- and D5-branes,  a la Strominger-Vafa), which no other theory of quantum gravity has been able to do so far

AdS/CFT can be related to well-established physical theories like QCD (even though the relation is not completely understood yet)

the ‘holographic principle’ can naturally be realized, for example in AdS/CFT, which in turn also implies an ‘IR/UV connection’ (two principles, which seem to be pivotal in the search for a quantum theory of gravity)

So, when I say, that string theory is intelligent design, I mean, that string theory is the result of years of clever research in trying to find the most fundamental theory of physics and actually – in contrast to ID – is trying to solve a problem, namely that of finding a quantum theory of gravity. In opposition to Lubos Motl, I would call string theory “the Apple of quantum gravity” and not the Microsoft of quantum gravity (but only in the sense, that string theory has proven to be extremely fruitful, both for physics and mathematics, and is built on a tower of innovative new ideas, much like Apple is – and not measured by how popular Microsoft vs. Apple is, where Lubos’ analogy of course is completely correct 😉