A couple of weeks ago I was interviewed for the Robots podcast special on on 50 years of robotics, and predictions for the next half century. My brief was nanorobots, and you can hear the podcast here. My pitch was that on the nanoscale we’d be looking to nature for inspiration, exploiting design principles such as self-assembly and macromolecular shape change; as a particularly exciting current development I singled out progress in DNA nanotechnology, and in particular the possibility of using this to do molecular logic. As it happens, last week’s edition of Nature included two very interesting papers reporting further developments in this area – Molecular robots guided by prescriptive landscapes from Erik Winfree’s group in Caltech, and A proximity-based programmable DNA nanoscale assembly line from Ned Seeman’s group in NYU.
The context and significance of these advances is well described in a News and Views article (full text); the references to nanorobots and nanoscale assembly lines have led to considerable publicity. James Hayton (who reads the Daily Mail so the rest of us don’t have to), in his 10e-9 blog comments very pertinently on the misleading use of classical nanobot imagery to illustrate this story. The Daily Mail isn’t the only culprit here – even the venerable Nature uses a still from the film Fantastic Voyage to illustrate their story, with the caption “although such machines are still a fantasy, molecular ‘robots’ made of DNA are under development.”
What’s wrong with these illustrations is that they are graphic representations of bad metaphors. DNA nanotechnology falls squarely in the soft nanotechnology paradigm – it depends on the weak interactions by which complementary sequences are recognised to enable the self-assembly of structures whose design is coded within the component molecules themselves, and macromolecular shape changes under the influence of Brownian motion to effect motion. Soft machines aren’t mechanical engineering shrunk, as I’ve written about at length on this blog and elsewhere.
But there’s another, more subtle point here. Our classical conception of a robot is something with sensors feeding information into a central computer, which responds to this sensory input by a computation, which is then effected by the communication of commands to the actuators that drive the robot’s actions. This separation of the “thinking” function of the robot from its sensing and action is something that we find very appealing; we are irresistibly drawn to the analogy with the way we have come to think about human beings since Descartes – as machines animated by an intelligence largely separate from our bodies.
What is striking about these rudimentary DNA robots is that what “intelligence” they possess – their capacity to sense the environment and process this information to determine which of a limited set of outcomes will be effected – arises from the molecules from which the robot is made and their interaction with a (specially designed) environment. There’s no sense in which the robot’s “program” is loaded into it; the program is implicit in the construction of the robot and its interaction with the environment. In this robot, “thought” and “action” are inseparable; the same molecules both store and process information and drive its motion.
In this, these proto-robots operate on similar general principles to bacteria, whose considerable information processing power arises from the interaction of many individual molecules with each other and with their physical environment (as beautifully described in Dennis Bray’s book Wetware: a computer in every living cell). Is this the only way to build a nanobot with the capacity to process and act on information about the environment? I’m not sure, but for the moment it seems to be the direction we’re moving in.