Carnal Reason

Seedmagazine has a fascinating new article that begins like this:

In the basement of a university in Lausanne, Switzerland sit four black boxes, each about the size of a refrigerator, and filled with 2,000 IBM microchips stacked in repeating rows. Together they form the processing core of a machine that can handle 22.8 trillion operations per second. It contains no moving parts and is eerily silent. When the computer is turned on, the only thing you can hear is the continuous sigh of the massive air conditioner. This is Blue Brain.

The name of the supercomputer is literal: Each of its microchips has been programmed to act just like a real neuron in a real brain. The behavior of the computer replicates, with shocking precision, the cellular events unfolding inside a mind. “This is the first model of the brain that has been built from the bottom-up,” says Henry Markram, a neuroscientist at Ecole Polytechnique Fédérale de Lausanne (EPFL) and the director of the Blue Brain project. “There are lots of models out there, but this is the only one that is totally biologically accurate. We began with the most basic facts about the brain and just worked from there.”

Before the Blue Brain project launched, Markram had likened it to the Human Genome Project, a comparison that some found ridiculous and others dismissed as mere self-promotion. When he launched the project in the summer of 2005, as a joint venture with IBM, there was still no shortage of skepticism. Scientists criticized the project as an expensive pipedream, a blatant waste of money and talent. Neuroscience didn’t need a supercomputer, they argued; it needed more molecular biologists. Terry Sejnowski, an eminent computational neuroscientist at the Salk Institute, declared that Blue Brain was “bound to fail,” for the mind remained too mysterious to model. But Markram’s attitude was very different. “I wanted to model the brain because we didn’t understand it,” he says. “The best way to figure out how something works is to try to build it from scratch.”

Markram believes a computer can become conscious. Eventually we’ll find out, but I don’t think so. It is easy to be seduced by the mystique of the supercomputer, but maybe a little less so if you understand how simple a system can perform any possible computation (assuming the truth of the Church-Turing thesis). Anything Markram’s banks of IBM microchips can compute can be computed by (among other systems) an SK combinator system. Here is how Wikipedia describes such a system.

K, when applied to any argument x, yields a one-argument constant function Kx , which, when applied to any argument, returns x:
Kxy → x
S is a substitution operator. It takes three arguments and then returns the first argument applied to the third, which is then applied to the result of the second argument applied to the third. More clearly:
Sxyz → xz(yz)
Example computation: SKSK evaluates to KK(SK) by the S-rule. Then if we evaluate KK(SK), we get K by the K-rule. As no further rule can be applied, the computation halts here.

That’s it. Two rules. Imagine a black box. Give it two terms, it returns the first. That is the K rule. The S rule is a bit more subtle, but still very simple. A system that can apply the S and K rules can perform any possible computation. I cannot believe an SK system could be conscious, and so do not believe a computer can be conscious. We’ll see.

Posted on March 4th, 2008 by pwyll
Filed under: science