Nanomaterials, and the nanotechnologies derived from them, are more limited than you might imagine. They’ve also been around a lot longer than you might imagine. A very early example of nanomaterials in use is the Roman manufactured Lycurgus Cup, the glass portion of which contains nanoparticles of gold. The effect is that depending on the direction of light through it (whether you are seeing the light reflected back or transmitted through the cup) it appears to be either green or red.
At one time there was a bit of Millennium Bug style scare around nanomachines – the Grey Goo scenario. This science fiction was based in part on a conflation of nanorobots and Von Neumanns machines (a theoretical self-replicating device). To explore why this is slightly problematic, we need to consider the big picture for a moment.
In the research community, you’d think we could come to some agreement about what nano actually means. Le Système International d’Unités gives an obvious starting point: 1 nm = 1 x 10-9 m, but the application of this can be somewhat more arbitrary. Physicists tend to say that if something is nanoscaled then it must be 100 nm or less in at least one dimension. I’ve always taken a more pragmatic approach: in terms of nanomaterials, it is the surface properties that become dominant, rather than the bulk. Whilst some surface properties are reliant on quantum effects, which do require smaller particle sizes to be observed, some occur simply because of the greatly increased surface area of very finely divided material – if we start with a particle of diameter ~10 μm and divide it into particles of ~10 nm then, whilst the total amount of material remains the same, the surface area will have increased by a factor of 1000. To put it another way, imagine that you and some friends meet up and divide into two groups. Bulk behaviour looks like the group looking mainly inward and holding hands with each other, with one person looking out and holding hands with the other group, whilst surface behaviours look more like the group looking outwards with everybody reaching out a hand to the other group.
Let’s take a look at this from another perspective. Nanoparticles are typically formed from only a few 10s to a few hundreds of atoms. If we want it to actually be active and move about then we need to provide it with some sort of power source. If we want it to carry out some kind of task then it needs to have the tools to be able to do this. If we want it to self-replicate then it not only needs to be able to store and use the information to do this, but it needs to be able to access the material and put it together.
Perhaps we need to be less literal? In the context of satellites, a nanosat weighs between 1 and 10 kg, in comparison to more typically examples massing a few thousand kg. When Iain M Banks talks about nanomissiles in ‘the Culture’ novels, perhaps he’s thinking in these terms. However, the problem remains that any small piece of equipment is likely to have to compromise on what it can achieve in terms of durability, mobility and range.
Or to put it another way the closest we get to life at the nanoscale is the humble virus, a piece of genetic code that can do three things: 1) Protect itself until it can 2) access a host and 3) cause problems by hijacking the host’s cells in order to allow it to replicate itself. Viruses aren’t truly alive though so we need to look to bacteria, which are typically 300-500 nm in size and are (sometimes) equipped to move themselves around their locale. It has been estimated that there are 5,000,000,000,000,000,000,000,000,000,000, (which, given our current knowledge of the universe means that there are more bacteria on Earth than there are stars in the sky). With around 1,000,000,000 in the mouth of someone who doesn’t brush their teeth regularly*, this number starts to make some sort of (frightening sense).
*If you brush, floss and all the rest of it this number can drop as low as 1,000.
Sometimes bacteria can coexist symbiotically with a host – we’d live very different lives if we didn’t have certain bacteria in our gut helping us to digest food. In that kind of scenario you can sort of imagine a nanorobot inside a host doing something – and of course there are all sorts of parasites that can cause changes to a host’s behaviour. But what isn’t credible is a nanorobot, perhaps a pilotless version of Tuck Pendleton’s craft (Inner Space), somehow hacking a human and taking over, or at the very least providing some sort of uplink.
To some extent we’ve got a bit distracted! Bacteria and Viruses don’t really have a part in materials science, although they are important in a couple of situations, and we might be coming back to those later in the month… The key point is that if you are working at the nanoscale then there are consequences, and you can’t take a homeopathic approach materials and just assume that something that works when the material is in the bulk will work the same (or better) when the material is reduced to a few thousands, hundreds of even tens of atoms. Which brings us to Jesson’s Law:
Nanomaterials do not give nanorobots.
Calling it Jesson’s Law, may be a tad grandiose, but it’s my blog, my rules, or in this case Law.