There are two questions: Is it possible for man to design a machine that can not only reproduce itself but also to be conscious and know it is doing so? The word "possible" has two possible meanings: is it technically possible and is it rationally possible based on what really grants us consciousness?
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Source: http://www.brunel.ac.uk/depts/AI/alife/al-vonca.htm
| Von Neumann's Self-Reproducing Cellular Automaton |
This is the problem of infinite regress in the "blueprint". Living organisms are finite and reproduce in a finite time. Any machine, whether in the real world, von Neumann's cellular space, or Life's cellular space, is likewise finite. If self-reproduction involves infinities, then it is pointless to look for self- reproducing machines.
The problem with machine reproduction is that the universal constructor is a mindless robot. It has to be told very explicitly what to do. If such a machine were given a description of an alleged self-reproducing machine, this constructor needs to understand that it is supposed to be reproducing the machine, including its description.
Von Neumann's solution was to append a "supervisory unit" to the machine to handle precisely such tasks (while enlarging the blueprint to include the supervisory unit as well as the universal constructor). Self-Reproduction can now occur in two phases. Firstly, under the guidance of the supervisory unit, the universal constructor builds a new universal constructor-plus-supervisory unit. When this construction is complete, the supervisory unit copies the blueprint and transfers the copy to the new machine.
Infinities are avoided because the blueprint does not try to encapsulate itself, but is interpreted in two ways. It is first interpreted literally, as a set of directions to be followed in order to make a certain type of machine. Once the self-reproduction has entered the second phase, the instructions in the Blueprint are ignored, and the blueprint is treated merely as data for the copying process.
Von Neumann began with a horizonless grid, with each cell in an inactive state. An organism was then introduced, covering two hundred thousand cells. the details of this creature were represented by different states of individual cells - there were 29 possible states. The different combinations of these states governed the behaviour of the organism, and defined the organism Itself.
It was shaped like a box with a very long tail; the box, about eighty cells long by four hundred cells wide, contained suborganisms:
A factory, (gathering 'materials' from the environment and arranging them according to instructions from another suborganism),
A duplicator (reading informational instructions and copying them),
A computer (the control apparatus);
These took up only a quarter of the creature's total number of cells. The rest of the cells were in a single-file line of 150,000 cells, acting as a blueprint for the instructions to construct the entire organism.
Once this automaton was embedded in the grid, each cell, as an individual finite state machine, began to follow the rule that applied to it. The effect of these local behaviours caused a global behaviour to emerge: the self-reproducing structure interacted with neighbouring cells and changed some of their states. It transformed them into the materials - in terms of cell states - that made up the original organism. The tail of the cell contained instructions for the body of the creature. Eventually, by following rules of transition (drawn up by Von Neumann), the organism made a duplicate of its main body; information was passed through an 'umbilical cord', from parent to child. The last step in the process was the duplication of the tail, and the detachment of the 'umbilical cord'. Two identical creatures, both capable of self-reproduction, were now on the grid.
"The Recursive Universe: Cosmic Complexity and the Limits of Scientific Knowledge" - William Poundstone
"Artificial Life : The Quest for a New Creation" - Steven Levy