Thermal Censorship of Ecophagy Study

The drafting of the NanoShield proposal [1] was in part a response to the original suggestion by Drexler [2] of the existential risk of “gray goo” and the subsequent technical analysis by Freitas [3] of the risk of ecophagy (both accidental and purposeful) in which carbon-based artificial mechanical replicators consume natural organic material that comprises the ecosphere of Earth. The existence of this risk is predicated on the assumption that molecular assemblers capable of atomically precise molecular manufacturing would function sufficiently reliably at room temperature to permit error-free multigenerational self-replication.

Freitas proposes a theoretical diamond mechanosynthesis (DMS)-related analysis to examine the temperature-sensitivity of diamondoid mechanosynthetic reactions and to assess the feasibility and reliability of room-temperature diamond-building reactions that might be employed by ecophages. This information is crucial to NanoShield because if diamondoid molecular manufacturing can only be done at liquid nitrogen temperature but not at room temperature, then: (a) ecophages will become much easier to defend against and (b) the world will become a measurably safer place. The NanoShield proposal could then be revised and extended to incorporate these new research results.

Proposal

Recent research by Freitas [4] (using the methods of computational chemistry including Density Functional Theory) examining specific reaction pathways for diamond mechanosynthesis (DMS) has hinted at the possibility that this assumption might be unwarranted. DMS appears to be extremely reliable at liquid nitrogen temperatures (~80 K).

However, there appear to be a number of competing reactions for several of the critical steps in building diamond structures that might become accessible to the tooltip chemistry at room temperature (~300 K) – the temperature at which ecophages would be expected to operate. If any of these competing pathways were taken during a DMS reaction sequence, the result would be the creation of a pathological molecular structure in the partially-completed product object (i.e., the daughter ecophage). That is, an irreversible structural error would be created during fabrication that could not be corrected, thus ruining the product object.

The operation of rigid diamondoid machinery such as bearings or gears inside an ecophage requires that almost every atom is in the correct place, or else the nanomechanical component will cease to function. During operation of a completed device, total device failure due to single-site errors can easily be avoided by employing a sufficient multiplicity of redundant components – if one subsystem fails, a duplicate backup subsystem can take over and functionality is not lost. However, during the manufacturing phase, an incorrect placement or misbonding of an atom can ruin the entire fabrication effort, since atom-by-atom mechanosynthesis is a sequential process with the placement of each atomic substituent depending critically upon the correct placement of preceding atoms.

A microscopic ecophage is not large enough to contain within itself either a large multiplicity of independent production lines or mechanisms for error-checking at each step, such as might be found inside a desktop nanofactory. Therefore the occurrence of a sufficient number of unrecoverable fabrication errors during the replication cycle of an ecophage would force the device to halt replication at some intermediate fabrication step. At that point the replication cycle could not be completed successfully and the attempt by the ecophage to replicate would fail.

Freitas’ research [4] has found that a number of DMS reactions (involving carbon structures) may develop significant reliability problems during high-temperature operation. A more focused study of the temperature sensitivity of DMS reactions is urgently needed and is strongly relevant to the risk we may face from future ecophages. If room temperature DMS cannot be made sufficiently reliable, this could impose a “Thermal Censorship” on nanomechanical ecophagy in which the ambient-temperature self-replication of diamond-based ecophages that acquire feedstock from natural organic matter might be prevented by the unreliability of the required foundational mechanosynthetic reactions.

Note that the unreliability of DMS at higher temperatures would not rule out the feasibility of diamondoid manufacturing [5] or desktop personal nanofactories [6]. Desktop nanofactories would incorporate small internal refrigeration units to create localized regions of low temperature where DMS could reliably take place. After the initial small feedstock atoms had been incorporated into larger nanoparts or nanoblocks, these larger components could then be reliably assembled into useful macroscale product objects at room temperature in the unrefrigerated spaces inside the nanofactory. Similarly, medical nanorobots [7–12] that employed no onboard DMS would still be able to function perfectly well as therapeutic devices at or near room temperature.

Budget

$10,000 in Fall of current year. $20,000 the following year ($10,000 in Spring and $10,000 in Fall).

Notes and References

1. Michael Vassar, Robert A. Freitas Jr., Lifeboat Foundation NanoShield Proposal, Lifeboat Foundation, 2006.
2. K. Eric Drexler, Engines of Creation: The Coming Era of Nanotechnology, Anchor Press/Doubleday, New York, 1986.
3. Robert A. Freitas Jr., Some Limits to Global Ecophagy by Biovorous Nanoreplicators, with Public Policy Recommendations, Zyvex preprint, April 2000.
4. Robert A. Freitas Jr., Ralph C. Merkle, A Minimal Toolset for Positional Diamond Mechanosynthesis, J. Comput. Theor. Nanosci. 4 (2007). In preparation.
5. Nanofactory Collaboration website.
6. Robert A. Freitas Jr., Economic Impact of the Personal Nanofactory, Nanotechnology Perceptions: A Review of Ultraprecision Engineering and Nanotechnology 2 (May 2006):111–126.
7. Robert A. Freitas Jr., Exploratory Design in Medical Nanotechnology: A Mechanical Artificial Red Cell (Respirocytes), Artificial Cells, Blood Substitutes, and Immobil. Biotech. 26 (1998):411–430.
8. Robert A. Freitas Jr., Clottocytes: Artificial Mechanical Platelets, Foresight Update No. 41, 30 June 2000, pp. 9–11.
9. Robert A. Freitas Jr., Nanodentistry, J. Amer. Dent. Assoc. 131 (November 2000):1559–1566.
10. Robert A. Freitas Jr., Christopher J. Phoenix, Vasculoid: A personal nanomedical appliance to replace human blood, J. Evol. Technol. 11 (April 2002):1–139.
11. Robert A. Freitas Jr., Microbivores: Artificial Mechanical Phagocytes using Digest and Discharge Protocol, J. Evol. Technol. 14 (April 2005):1–52.
12. Robert A. Freitas Jr., Pharmacytes: An Ideal Vehicle for Targeted Drug Delivery, J. Nanosci. Nanotechnol. 6 (September/October 2006):2769–2775.