Computation as the Ultimate Metaphor
Rodney Brook, an AI professor at MIT and author of Flesh and Machine, wrote this response "Computation as the Ultimate Metaphor" to a question posed by the Edge Foundation, "What have you changed your mind about during the 2007?"
The Edge Foundation is a site that I have long subscribed to by email. [No RSS feed is available]. The Edge promotes discussion by the "third culture," which, according to its words, consists
of those scientists and other thinkers in the empirical world, who through their work and expository writing, are taking the place of the traditional intellectual in rendering visible the deeper meanings of our lives, redefining who and what we are.
Rodney recently questioned his belief in computation as the ultimate metaphor. Computer scientists, he writes, are ultimately biased towards their discipline when they attempt to explain human behavior in terms of computers, just as molecular biologists see their "their level of mechanistic explanation as being ultimately adequate for high level mechanistic descriptions such as physiology and neuroscience to build on as a foundation."
Those of us who are computer scientists by training, and I'm afraid many collaterally damaged scientists of other stripes, tend to use computation as the mechanistic level of explanation for how living systems behave and "think". I originally gleefully embraced the computational metaphor.
Such a pattern, he argues, in fact recurs regularly at different stages in the history of technological advancements.
If we look back over recent centuries we will see the brain described as a hydrodynamic machine, clockwork, and as a steam engine. When I was a child in the 1950's I read that the human brain was a telephone switching network. Later it became a digital computer, and then a massively parallel digital computer. A few years ago someone put up their hand after a talk I had given at the University of Utah and asked a question I had been waiting for for a couple of years: "Isn't the human brain just like the world wide web?". The brain always seems to be one of the most advanced technologies that we humans currently have.
I must admit that I do subscribe to the view of computation as the ultimate metaphor, at least in its applicability to the human thought process. While I admit that I may be biased as a software developer, I still retain that belief despite his arguments. It may even be true that the both the computer scientist and the molecular biologist are both right in their thinking, but that each one is exploring a different facet of human behavior that is more appropriate to each discipline.
The universe is a computer, and everything that happens in it--everything produced--is the result of a computation. Everything is a program. By the principle of universality, we can construct a functional expression for it all. My static analysis tool, for example, instantly produces a functional expression for every variable in the program. Each expression is basically a program showing how the value could be computed, but the expression can also be viewed as the value itself, possibly unsimplified.
The same applies to our thoughts and all our natural language utterances. My own work focuses on representing and manipulating natural language as little programs or functional expressions rather than using traditional forms of knowledge representation. Words are "evaluated" by applying their definitions. This has the nice benefit of a tighter relationship between syntax and semantics, better handling of ambiguity, and ease of use similar to other primitive data types. I only became aware of other research manipulating natural language in a functional way through this paper entitled "Realization of Natural Language Interfaces Using Lazy Functional Programming" mentioned in Lambda the Ultimate. "Oh, my god! they stole my idea," I thought until I discovered that functional Montague grammars were invented way back in the 1960s.