Nanites

Interesting, I wonder how they get around the temperature gradient problem.

This is the problem that these systems usually only work when there is a temperature difference between the receiving object (in this case the quantum dot) and the surrounding environment.

In large scale applications you can use external cooling to resolve this issue but it is a massive issue at the nano scale.

Joat42 wrote:Powering nanites can be done in a couple of different ways

1. Mimic organic cells and use chemical reactions to harvest energy.
2. Fuel-cell type of power, for fuel use the alcohol the body produces naturally (~0.2 mg per 100 ml blood).
3. Use ambient RF for power.
4. Sci-fi, future tech allows the nanites to be powered by cosmic rays
5. Sci-fi, future tech has extremely small capacitors which has extreme energy density.
6. Sci-fi?, powered by body-heat - ie. energy is harvested from molecular vibrations.

Using the same sources of stored chemical energy as the cells in your body would be the obvious way to power medical nanites. This would of course mean you'd have to eat noticeably more while a major injury was being repaired, both for energy and raw materials. Nanites on the surface of your skin could conceivably generate usable power from ambient light. Call them NPVs (nano-photovoltaics). You'd have to figure out how to funnel that power to nanos in your bloodstream and throughout your soft tissue, obviously.

I think chemical energy will probably be the way to go. Which brings up another point, one I rarely see discussed. Energy balance in reactions involving nanites is critical. For example if you wanted medical regeneration to go super-fast, so someone could sit there pumping bullets into you and the wounds would heal up right before your eyes, that's almost certainly not feasible. If for no other reason than the energy balance would have to be exactly zero sum. If the net result of the reactions was even slightly exothermic, you'd spontaneously combust. If it was even slightly endothermic, you'd freeze solid. Healing could only proceed so quickly and still be safe. This is also why you couldn't power med-bots thermally. They'd turn you into a human cold pack, your body temperature would drop to subfreezing levels within a very short time.

Not all "grey goo" scenarios are possible. Again, it depends on whether the reaction in question is exothermic or endothermic. If energy must be supplied from the outside runaway incidents could only happen if those nanites were also designed to scavenge energy from the environment. On the other hand, if energy is liberated by the reaction a runaway replication disaster could happen with much cruder nanos. Methods for neutralizing uncontrolled replicators will have to be developed before self-replicating nanites of any kind are allowed into use.

I think a lot of safeguards will be built into real nanotechnology, especially in the medical area. You'd want to customize them to each person and make sure they were physically unable to survive outside the body of their "host". This would mean they wouldn't pass down from mother to child. The baby would have to be injected with a new batch, prepared especially for them. Much of the work of designing nano-systems will involve safety measures; making sure the tiny machines can only replicate if certain conditions are met, that they can only survive in specific environments and will break down immediately under any other conditions, etc. Enough limitations and the slightest change to a nanite (call them mutations if you like) automatically destroys it. If you want a system that can operate forever in total safety, those are the sort of design standards that need to be met.