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The Grey Goo ScenarioThe threat from nanotechnologyNew technologies give rise to new forms of old fears. Just as people were once anxious about the possibility of robots taking over the world the fear is now that their nanotech equivalents could reduce the world to one big sticky mess. One feature of nanotechnology will be that the nano-structures replicate themselves. They are so small and they are needed on such a large scale (billions of nano-hairs to cover the area of a gecko toe, for instance) that it is just not feasible for people to make them individually. The gecko hairs will either have to build themselves or be built by other nano-devices, in the same way that strands of DNA are able to construct new protein molecules. Like little engines, to do their nano-construction work they need fuel. One plan is for them to use organic compounds like carbohydrates in much the same way as living organisms do to get their energy. In the beginning the whole process of nano-production might be perfectly controllable in the lab, but the fear is that once out in the environment things could change. Unpredictable reactions could lead to a mutation and a new form of nano-reproduction that could not be countered. The result would be a huge sticky or gooey mess spreading over the face of the planet, consuming all organic compounds in its path. It would eat everything and effectively turn the earth into one big desert. This worst-case scenario has been termed global ecophagy (the total consumption of the world�s ecosystems), but it is known more widely as the grey goo scenario. Defenders of nanotechnology try to assuage these fears by pointing out that smaller objects are more susceptible to damage from radiation and heat (due to greater surface area-to-volume ratios), so nanomachines would quickly fail when exposed to harsh climates. There is now a consensus amongst scientists that the grey goo scenario is highly unlikely. However, other risks have been identified. Critics of nanotechnology point to the potential toxicity of new classes of nanosubstances that could adversely affect the stability of cell walls or disturb the immune system when inhaled or digested. These new substances could be as toxic as the microscopic asbestos fibres that can cause so much damage to the lungs. There is also a possibility that nanoparticles in drinking water could be dangerous to humans and/or other animals. Intestine cells exposed to nano titanium dioxide particles have been found to decay at a quicker than normal rate. (Disturbingly, these particles are already used in some sunscreens to make them transparent.)
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