The futurist literature has conjured two different machines related to this idea. The first is a molecular assembler, a machine of nanotechnology which manipulates actual molecules. The other is a Kinematic self-replicator which simply manufactures a copy of itself using macro-scale manufacturing techniques like additive 3D printing. Google, wikipedia and internet slang in general has recently taken up the phrase "clanking replicator" to stand for a Kinematic self-replicator.
- http://en.wikipedia.org/wiki/Assembler_ ... hnology%29
Here is the rub. No one on earth has successfully built a self-replicating machine. Neither have they achieved this feat at the molecular nor the macro-scales. Los Alamos National Laboratories has not succeeded, nor has NASA, nor have the various laboratories of Switzerland, Germany, Austria or France. The Chinese have not succeeded. Erasing all economic factors of profit margin and the like, no such thing has even been shown to exist even in a lab setting. We don't even possess a prototype showing feasibility.
In this article we will investigate why this engineering project has continued to fail. I will do so by brainstorming various plausible reasons and just collecting them in a list. This list should be interpreted as pure speculation. Since no prototype exists in a lab, speculation of this kind can and should play a constructive role in our dialogue.
- Macro-scale self-replication is simply put, mathematically impossible? Only molecular replication near the quantum scales is possible? This may sound silly, but the hypothesis is grounded. The strong magnetic alignment of molecules, and their requisite folding is not something observed in the solids of this large world we occupy. These self-aligning properties are de novo existing in atoms and molecules. The strong linking and breaking of bonds is reproducible for macroscopic objects only under duress of engineering, but comes as natural physics for atoms. Potassium will react strongly with water, not because some clever engineer made it do that, but because the universe just does that naturally.
- Eric Drexler is just wrong about the world at molecular scales. Molecules (and atoms) are not little solid bb bullets connected by strings. Rather they are quantum-mechanical objects which shake rapidly all over when they are at room temperature. (molecular shaking is more rapid than anything you can imagine. It is quantum shaking). Lets enumerate some other reasons why Drexler is wrong about molecules. Many bonds formed between atoms are highly sensitive to heat and pressure. This should be obvious from the plethora of phase-transition diagrams. The difference between gas, solid, and liquid phases of matter are often not even related to chemical bonds at all, but simply the result of van der waals forces. In addition to the sensitivity of crystalization due to temperature and pressure, there is also the issue of solubility. This can take place even when a sample is being bombarded by a gas. That is to say, even the nearby gas surrounding a sample can dissolve a solid. http://en.wikipedia.org/wiki/Phase_transition
- We have to revisit the teleological arguments from the Enlightenment philosophy of the 17th and 18th centuries. This issue may become pressing if we imagine taking a reprap 3D printer, and demanding it replicate a copy of itself without human intervention. Repraps assume the owner has access to a "workstation" PC which is modern and capable of holding the giant 3D mesh data that will be reproduced by the printer. To get true honest-to-god self-replication, we would, in some sense, need to print the workstation -- also. Slowly but surely a nagging problem arises. The workstation that is capable of printing our original workstation would need to be bigger and more complex than the one in which it prints. This logic then cascades into an upward spiral, where each successive workstation would need only a bigger and more complex workstation to print it, up and up. Something has to give.
- The watchmaker argument of William Paley creeps in. Kinematic Self-replication may be impossible because of Paley's "principle". A complex item must infer a designer, who is presumably more complicated than his designed artifact. Living organisms are not subject to the "Paley Principle" because living organisms replicate a molecule in the nucleus of their cells. That is molecular self-replication, not the kinematic manufacturing type we might desire.
- One argument that floating around the philosophical circles is the following. The infinite regress to "larger and larger workstations" actually ends at some point. This is an article of faith. It claims there is some upper limit of complexity, upon which a workstation will possess the needed capacity (processing and RAM) to make a reliable copy of itself. (I don't personally buy into this reasoning).
- So the debate comes to a head. Either self-replication has not been obtained yet because we most seek out for it within the domain of very high complexity -- or self-replication must be found in simplicity of molecules and atoms.