Self replication

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

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 robotic units must be complex enough to fulfill their task
• All robotic units must share a part of the movement mechanism and their hole control system (note prductivity issue here).

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.

This method 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 assembly level.

Note: Do not mix this up 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.

Videos: [1]; Paper: [2]

It was believed that self replication is impossible to circumvent. This method should deliver a counterexample.

Block based self replication

A less top down alternative for exponential assembly would be block based self replication. 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. There must be a method to feed the units with new blocks. Steering could be done e.g. by local broadcasting electrostatically from a chips surface.

Diamondoid self replication

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 and raised rather uninformed concerns about runaway assemblers wreaking havoc. Furthermore the direct mechanosynthetisation of bigger structures necessary for a proto-assembler turned out to be a too steep slope without stepping stones. There are much more starting points for incremental technology improvement instead.

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

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 get to the upper edge of self assemblabel structures. 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