Scientists are discovering entire worlds of new information in the field of nanotechnology. The properties of substances at the nanoscale are different to those same substances in bulk. For example, substances that are insulators might become semiconductors at nanoscale, and melting points might vary in the same way. Taking advantage of manipulating atoms at nanoscale, scientists are experimenting with ways to use nanoparticles in various applications to create almost anything.

The gray goo scenario was first articulated by K. Eric Drexler -- an engineer and nanotechnology theorist. The problem goes like this: In order to build objects one molecule at a time, you need a nanomachine called an assembler. This is a device that is made of only a small collection of molecules itself -- it is too tiny to see, and it works with materials on such an infinitesimal scale that it couldn't ever get anything significant done on its own. That's why assemblers would have to be programmed to build other assemblers -- essentially, to self-replicate by building copies of themselves out of surrounding molecules. Once an assembler has enough buddies, it can get some serious work done. From a technological standpoint, this scenario is exciting and productive. However, Drexler's question was, essentially, the following: What if we lose control of these nanomachines? Could they convert all living matter into assemblers, effectively devouring the planet with a mass of gray goo?

Right now, this scenario is impossible, since we're probably decades away from building anything that would resemble an assembler in Drexler's vision. Other futurists feel that as long as we design the right precautionary measures and remain vigilant, the gray goo scenario won't happen. After all, before a mass of molecular assemblers can experience exponential growth and global supremacy, it goes through a long period of weakness and vulnerability in its small numbers, during which it could easily be contained. Other engineers question whether we'll ever be able to build a meaningful device on the nanoscale at all. If we can't, it makes the question moot. In short, the scenario is impossible now and unlikely in the future.