Latest revision as of 19:25, 15 September 2024

Up: Intuitive feel

(wiki-TODO: Add a scaling square illustration with all four combinations of space and time scaling)

Speeds of motion in nanorobotics

Today it's general education that temperature is equivalent to the speed of motion of particles at the atomic scale. If you unfamiliar with this "thermal motion" also known as "brownian motion" I suggest you read up on this elsewhere (e.g. wikipedia) before continuing here.

The incredible rate things zap past their surroundings (just driven by temperature)

Thermal motion at the nanoscale is pretty incredible.
Small single molecules zip around at thermal speeds of a few hundred meters per second. That's about the speed of sound. When we scale up size by our usual magnification factor of 500.000 to make model atoms (say water molecules) have the diameter of a human hair and when we keep the flow of time unchanged then those hair sized molecules zip around with more than half the speed of light.

But since those water molecules are densely packed they do not move in long straight lines.

• In liquid phase (e.g. water) they move in twisty paths with curve radii of about their own size.
• In one atmosphere gas phase (e.g. air) they move about 250 times their size (the mean free path length) before colliding and making a more or less U turn. In the 500,000 times scaled up model those U-turns are executed at near the speed of light every 2.5 centimeters (250 x 0.1mm).

Note that molecules in a liquid or gas that are not bond to a crystal run apart quantum-blurrily quite quickly (more on that later). So a "soup" of a superposition of all possible collision-histories is a better picture for fluids and gasses.

Assembly by mindlessly throwing parts together at ridiculous rates

Given this situation it becomes very obvious that in a liquid environment that is densely packed with other solvent molecules (e.g. water) solvated molecules meet a lot of other solvated molecules in a very short amount of time. Bigger more massive molecules like proteins ("puzzle piece molecules") move slower but collision rates are still very very high.

This is why puzzle piece shaped proteins molecules in biological systems can "assemble themselves" into their intended products. Via their random collisions they just mindlessly try all possible places they could bond to in very very fast succession. It's mindless trying like having toddlers that do not yet grasp that cubes do not fit through round holes do the assembly job but since it's done so fast (like brute force computer algorithms) useful things can be assembled nonetheless.

The technical term for this method of assembly is "self assembly" but here we'll call it "thermally driven assembly" which captures the meaning better. On the day to day macroscale this method of assembly is usually not applied for practical purposes due to its ridiculous slowness and requirement of parts fitting together like a sticky puzzle. Fully grasping the process how it happens at the nanoscale at an intuitive level may be impossible due to the vast number of trials until the final successful bonding reaction. (TODO: investigate better visualization methods) There are beautiful CG videos of molecular biology that use fake motions mo make it comprehensible (wiki-TODO: add link).

Use of thermally driven assembly to get away from thermally driven assembly ASAP

Thermally driven assembly is the predominant form of assembly in biological systems. Thermally driven assembly of increasingly artificial molecules will be (and already is!!) a very useful tool for walking the initial steps of the path to advanced nanofactories. But as it turns out in an advanced nanofactory (the far term goal) it makes much more sense to actually constrain / suppress thermal vibrations and take care of the transport oneself in a fully controlled and less mindless fashion.

The idea of working towards a point where we deny the help of thermal motion (shunning the teachings of nature) but doing assembly tightly controlled and guided instead has received harsh criticism in the past. It was and still is often misunderstood as a misunderstading of the real nature of the nanocosm.

But there actually is an example where we already succeeded with the suppression of thermal noise. Nanoelectronics. In microchips we've already learned to suppress thermally caused electrical noise without even noticing it since it just gradually got more difficult.

The two necessary requirements for thermal noise suppression are the same that we used to get away from analog technology namely:

• error margins and
• error correction

Now we use mostly digital electronics.

Given that electrons start to behave strongly quantum-mechanically in the nanoscale (quantum blurriness and thermal motion can often be treated in a common fashion) -- which stands is in stark contrast to nanomechanical nanomachines -- this is even more of a feat. We where not forced to switch some sort of probabilistic electronics (whatever that would be). Since much less quantum mechanical in behavior advanced nanomechanical systems will have even less reason to work in a purely probabilistic fashion.

The smaller the more productive

Main article: "Higher productivity of smaller machinery"

While size goes down speed goes up. A good example in nature is the increasing wing flapping rate seen in birds and insects.

By naively scaling down a current day 3D-printer by a factor of 500.000 (just for illustration - not a serious proposal) it becomes 500.000 times faster. A typically time for 3D printers to print parts that have about the mass of the printer itself is on the order of 10 hours. This shrinks down to just 0.72 seconds.

Now a single shrunk down printer won't produce much but imagine the whole volume of the original non-shrunk printer filled up with shrunk down printers. This would then produce the macroscale printers own mass in less than a second.

In a serious advanced nanofactory design the time to produce the production machinery's own mass can become even smaller due to better materials, lower friction, smaller size steps, to name a few reasons. For a good intuitive feel about the production rate imagine products shooting out like rifle bullets.

I fact the time to produce production machinery's own mass can become so short that the products that can be produced at the nanoscale cannot be fed out fast enough at the macroscale anymore. Getting even remotely near there would require impractical levels of cooling.

Solution: One humbly accepts not to get the full crazy level potential of nanoscale production machinery and is content with just more than practical levels of productivity.

To do this one does not fill up the whole volume with productive nanosystems. One abandons the concept of clouds of molecular assemblers. Instead one integrates everything in a thin chip. A nanofactory. For details check the main article: Macroscale slowness bottleneck

Even in the case when one really wants to push the limits (there's likely military interest here) its likely that a highly advanced fractal nanofactory that is a little thicker is the best solution. For a continuously running device the cooling facilities then are likely much bigger than the productive device itself. The production becomes highly inefficient and turns a lot of energy into heat. Still there is the fundamental specific acceleration limit which cannot be exceeded. This is the point where no known material would not break from the acceleration loads.

Motions in the far term goal of advanced nanofactories

Assembly in an advanced nanofactory will resemble more of a factory assembly line far away from any similarity to biological systems. All the machinery will usually run much slower than the thermal motions (about at least a factor of 1000 but more like a factor of 100000) but since every try is a hit (for all practical purposes) the production throughput can be the same or higher than the one of natural bio-systems that work with thermally driven assembly.

In rare occasions one might want to let go of molecules or crystolecules in an advanced nanosystem. Thermal motion for bigger crystolecules in a vacuum under gravity are statistically distributed throwing parabolas. Single molecules show significant quantum blurring when released.

• Envelope of throwing trajectories with same speed
• Throwing trajectories with various speed in same direction

Related

• The challenge of high speeds near nanoscale
• Intuitive feel
• Atom placement frequency