Drexler more recently conceded that there is no need to build anything that even resembles a potential runaway replicator. This would avoid the problem entirely. In a paper in the journal Nanotechnology, he argues that self-replicating machines are needlessly complex and inefficient. His 1992 technical book on advanced nanotechnologies Nanosystems: Molecular Machinery, Manufacturing, and Computation describes manufacturing systems that are desktop-scale factories with specialized machines in fixed locations and conveyor belts to move parts from place to place. Popular culture, however, remains focused on imagined scenarios derived from his older ideas. None of these measures would prevent a party creating a weaponized grey goo, were such a thing possible.
In Britain, Prince Charles called upon the Royal Society to investigate the "enormous environmental and social risks" of nanotechnology in a planned report, leading to much delighted media commentary on grey goo. The Royal Society's report on nanoscience was released on 29 July 2004, and dismisses the idea as impossible.
More recent analysis has shown that the danger of grey goo is far less likely than originally thought.However, other long-term major risks to society and the environment from nanotechnology have been identified. Drexler has made a somewhat public effort to retract his grey goo hypothesis, in an effort to focus the debate on more realistic threats associated with knowledge-enabled nanoterrorism and other misuses.