Yes, Chris, I am aware that the whole point of the MNT paradigm is to create idealized conditions and work with idealized materials, where it is not needed to know everything that is going on. Models tell you what should be going on, and it is expected that in the eutatic environment there will be little deviation between theory and reality. The sort of devices imagined in the MNT program only can move in a very small number of ways. That is why it’s all about diamond or other covalent solids. Maybe, the MNT program won’t need exotic methods of observation to work in practice. At least we have a theoretical framework for such methods if they are needed.

The role counterfactual measurement might be able play in nanotechnology is unclear. It is still a relatively new field. It will probably be integral to the design of any practical, scaleable quantum computer. If we had a decent quantum computer now, this whole issue of the feasibility of a software-controlled matter compiler would be much easier to settle. We could see rather quickly what is most likely to work and not to work. As an example of where we are with simulations, take proteins. The only simulations of proteins that are practical are ones based on protein design, general folding is still a big problem. This limits you to a set of ones that can be easily designed. If we had a mature form of microscopy based on counterfactual measurement, might we have a better understanding on how proteins fold in sutu?

I admit, Chris, you made a pretty persuasive argument in one you previous essays that mature MNT could be very powerful even with a rather impoverished set of reactions. The analogy of a digital computer is a good one. It only does a handful of things well, but these operations can be combined in a myriad ways to produce a vast array of applications. The same could be true in nanotechnology, but this early in the game let’s try to not limit ourselves to processes that are easily visualized in simulations. The problem with that is, what is easy to model and what is easy to do are totally different things. This is what I think has created so much confusion about Drexler’s ideas. They are simple and easy on one level, but on the construction front they are very hard or impossible with current tools. Hopefully, we will soon be able to test the basic reactions in diamond mechanosynthesis. (Maybe this Ideas Factory will fund such an effort!) That would be a huge achievement in itself, but it would not prove the entire enterprise. And even if you knew for sure an MNT style, neat and clean nanofactory was possible, you would still have to build it. That is daunting task to say the least. We don’t know how many messy processes will be needed to make the first nanofactory.

The point I was making about being able to see like we do at the macroscale is that, at the macroscale, the interference caused by observation does not appreciably change what we are looking at. That is the feature of seeing at the macroscale that I hope quantum interrogation can bring to the nanoscale.

In short, the technology of interaction-free measurement or quantum interrogation is still new. It may or may not be needed in the normal operation of a device that can build through the software control of matter. Indeed, it would be easier to not have to deal with the extra complexity. However, there may be phenomena of interest to nanotechnologists that can only be directly viewed in this manner; as simulations are a rather indirect way to learn about the world around us.

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