Revision as of 20:41, 30 April 2014

Self replication is of interest for attempts to attain atomically precise manufacturing (APM) because it is one of the methods that allows for massively parallel assembly.

Putting together an macroscopic object (consising out of some 10²³ atoms) almost atom by atom is a goal of AP Technology. It would take unfathomable amounts of time if it where done with only one robotic device. Massively parallel assembly is thus a necessity.

Classification based on base-structur size

Exponential assembly

First few steps of partial structural replication via so called "exponential assembly". SVG

Exponential assembly is a method of structural copying with exponential speedup.

It has the following defining traits:

• The un-assembled robotic units must be massively parallel pre-produced without self replication. (photo lithograpy / self assembly)
• The un-assembled robotic units must be layed out in a perfectly orderly fashion over great relative distances.
• The robotic units must be just complex enough to fulfill their task.
• All robotic units must share a part of the movement mechanism and their hole control system (note the productivity issue here).

To attain technology level I such systems could be used to assemble smaller systems of the same exponential assembly design but possibly (and probably) of very different structure. Maybe: top level: MEMS system; bottom level: structural DNA nanotechnology. In that case the components for exponential assembly at the self assembled bottom-up side will look very different than the MEMS on the top down side since they are built with very different constructuion methods.

Exponential assembly is claimed to not be true self replication since the units on their own lack functional completeness and the posible range of structural replication is thus limited to the size of the topmost exponential assembly level. It was believed that to gain AP control over matter self replication is impossible to circumvent. This method should deliver a counterexample.

Videos: [1]; Paper: [2]

Note: Do not mix up exponential assembly with convergent assembly. Convergent assembly in contrast:

• works the other way around (bottom-up)
• is used for efficient product production not technology attainment
• has potentially more layers in the mesoscale that only differ in size not material.

Paper about exponential assembly: [3]

Block based self replication

A less top down alternative for exponential assembly would be block based self replication (using e.g. structural DNA nanotechnology). traits:

• The robotic units consist out of simple basic blocks that can bind together. (complementary shape?)
• The robotic units as a whole must be complex enough to fulfill their task.
• A proto-robotic-unit (mechanism/linkage) must be assembled "manually" from the blocks.
• Steering could be done e.g. by local broadcasting electrostatically from a chips surface.
• There must be a method to feed the units with new blocks. (bulldozing & shape checking??)

Diamondoid self replication

Nanofactories of technology level III will be capable of doing diamondoid self replication as a whole.

The original idea to make APM a reality was to build a diamondoid nanomachine of technology level III capable of self replication also known as molecular assembler. The attempt to directly build a proto-assembler with just a single AFM/STM microscope forces one to pack the whole replicative functionality into a very small package. This would make the unit inefficient. Furthermore the direct mechanosynthetisation of bigger structures necessary for a proto-assembler turned out to be a too steep slope without stepping stones (at least till the point of this writing 2014). There seem to be much more starting points for incremental technology improvement instead.

The idea of Assemblers blown up by the SciFi writers movies & co raised rather uninformed public concerns about runaway assemblers wreaking havoc. For the science community the "nano" tag meant/means(2014) funding money. But nano came with the meaning of APM embedded which they had nothing to do with. Then APM became linked with the (actually bogus) killer-nano-bugs. It seems some wanted to get rid of that (publicly as direct perceived) association. The prejudice of infeasability from focused technical expertise may have played a role too. This culminated in the removal of anything APM related from the american national nanotechnology initiative NNI and drastic funding drop for APM development [TODO: check this].
See: history page for more details

General

For the attainment of technology level I either exponential assembly or block based self replication will be needed. Modular molecular composite nanosystems (MMCS) might be employed to organize self assembled structures of the upper size edge. The usage of standard blocks or other prebuilt AP structures for structural replication has the advantages that:

• the needed accuracy is lower (click to place)
• contrary to diamond mechanosynthesis no vacuum is needed
• contrary to molecular moieties prebuild structures can be stuck to a surface by drying and possibly cooling.

The other two methods for massively parallel assembly (or construction) known today are:

• photo lithography for MEMS (not scalable to arbitrary small size scales; used in exponential assembly)
• self-assembly (not scalable to arbitrary big size scales; used in block based self replication and possibly in exponential assembly)

For a more broad definition of self replication there is already a lot of literature to consult:
Wikipedia: Self-replicating_machine; The "Bunny Book": Kinematic_Self-Replicating_Machines; In general: Self-replication