On the impossibility of grey goo

 The proposition is that it is possible to create swarms of self-replicating “nanobots” that will pose a threat to mankind and the earth. We can examine it under a few headings:


Small particles inhabit a physical world that is dominated by viscosity (for the technically minded low Reynold’s Number and Stokes’ Law). Virtually their only mode of motion is in currents of air or water, like motes in a sunbeam. In the living world there are no examples of micro-organisms making significant automotive progress in air. In water some organisms move by means of cilia, flagella or the more curious amoebic motion. Even a plant (chlamydomonas) is capable of movement towards light by means of cilia. Speeds of protozoa range from about 5 micrometres a second for amoebae to about 1000 micrometres a second for the slipper animalcule (paramecium). Less than four metres an hour seems hardly a good basis for invading humanity. Of course, a protozoon can bring down a man with, say, amoebic dysentery, but this is by a process of ingestion and reproduction. For progress across dry surfaces you have to go to higher life forms such as mites.

 Logical problems

Assume you set out to design a self-replicating entity and you decide to add a feature. You then have the following logical problem:

1.      Add a feature

2.      Add the ability to manufacture this feature

3.      But in doing so you have now added another feature

4.      So, back to 1.

You now have a feedback process with exponential instability. The problems grow and grow without a means of termination.

 Material problems

The first choice you have to make is what materials you are going to exploit. In manufacture, materials have to be either synthetised or mined, refined and manipulated. These materials have got to be available at all times or the self-replication will come to a halt. The processes all require large amounts of energy. Silicon is the most abundant material on the surface of the Earth and, as it happens, it is the basis of all existing micro- and nano-technology, if only as a substrate. However, its purification and processing require vast plants of equipment and copious amounts of energy. Zone refining demands high temperatures and refractory materials, while etching involves highly reactive chemicals under carefully controlled conditions. The original startling demonstration of nanotechnology, the delineation of the letters IBM in individual atoms, needed the vast technical resources of scanning force microscopy. No one has yet seriously suggested the possibility of a small-scale replacement. Nano-scale integrated circuits and electromechanical devices may well be in the offing, but that is a long, long way from self-replication.


A robot of any kind needs a source of energy and a means of storing it. Life works on solar energy. Chlamydomonas traps it by photosynthesis. Amoebae and paramecia rely on smaller plants, known as diatoms, to gather it before they are harvested. The proponents of grey goo do not offer a solution to the problem of the energy source.

The suggestion of solar energy as a direct solution of the problem is simply a repetition of the solar fraud. We are not told how big a nanobot is, but assuming it is a square of 100 micrometres side the solar power available would be considerably less than a microwatt (when the sun shines). Now you could possibly run a digital processor and memory on such a restricted source of power (in fact I did so in my own laboratory with optically powered sensors) but turning it into mechanical power is a different kettle of clichés. Of course, the nanobots might get their energy from eating human beings, but there is a substantial problem of chemical processing involved, which would be a trifle difficult to realise in such a restricted volume (yes, I know bacteria manage it, but we are not talking about life) and there is the problem of storing the energy between meals of humans. Compact energy storage is one of the great unsolved technological problems, which is why we don’t have roads crowded with electric cars.


Micro-electronics has made enormous strides in miniaturisation but it is still far short of what evolution has achieved. Darwin described the brain of the lowly ant as the most remarkable speck of matter in the world. The ant, which is orders of magnitude bigger than the posited nanobots, has about 250,000 brain cells. A human brain has 10,000 million, so a colony of 40,000 ants has collectively the same size brain as a human. Humans solve problems by reason, while ants solve them by trial and error. If you have ever had your house invaded by ants you come to realise that the question of which is better is a close run thing.

The nanobots are supposed not only to store the information they require for their day to day tasks, such as destroying the human race, but also the whole blue print for manufacturing their own kind. Living things do not work this way. The strand of DNA contains a program to control a development process in the egg or womb that rehearses the whole evolutionary process. The human embryo has gill clefts and a post anal tail. If the human brain had to contain the information to build a human it would be the size of a planet. You would have to add to this the contents of a brain the size of a planet and you would have to add to this the contents of a brain the size of a planet plus the contents of a brain the size of a planet and so on. Of course, it can be claimed that the nanobots will replicate the evolutionary process, but how? Will they have nano-wombs?

The counter argument

The obvious analogy for the nanobot proponents to pursue is that of flight by heavier than air machines. Many great scientists of the preflight era contended that it was a fantasy. Perhaps the most famous was Lord Kelvin, president, Royal Society, 1895  "Heavier-than-air flying machines are impossible."  Another was Simon Newcomb, a noted American astronomer, who wrote copiously on the matter, with cogent arguments that were consistent with the science of the time. However, he did in fact  concede that human flight might one day be possible, but only by the discovery of some completely new material or force of nature, which  is just what happened. The Wright Brothers employed principles of Aerodynamics and Fluid Mechanics that were completely unknown to Physics at the time and which they did not understand. 

There are a number of differences. Kelvin and Newcomb were writing in an age of  invention, daring and aspiration. Many people died to prove them wrong. We now live in a post-scientific age of religiosity, scares and the precautionary principle. Mathematical physics was then primitive and inadequate. It is now relatively powerful and complete. We do not yet have the theory of everything, but most physical phenomena are readily explicable. Science fiction is a  a genre that offers great entertainment. It usually works by suspending at least one established scientific principle and we suspend disbelief for the sake of the enjoyment. The relativistic limitations of the vastness of time and space, for example,  are overcome by the fictional invention of hyperspace, so that Captain Kirk and company can voyage through space and time to encounter other life forms who conveniently speak American. One of the problems of our age is that science fact and science fiction have merged in the popular consciousness. This is exploited by the neo-Luddites, who find reasons for opposing every scientific advance and urge a return to the values of the New Stone Age. Nanotechnology, primitive and over-hyped as it is, has joined genetic modification, mobile phones and all the other manifestations of the the technologically advanced society as the epitome of evil, only to be obviated by embracing the new  eco-theology.

What is the alternative?

 Recipe – take one atmosphere of nitrogen, carbon dioxide and other trace materials. Subject it to copious electric discharges to encourage ionisation and agglomeration. Add the product to a quantity of water containing various salts – an ocean would be a convenient container. Wait for a few million years for the soup to mature.

December 03 

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