The concept of a tipping point is familiar: A generally stable system evolves to where the stability disappears and the system suddenly and irreversibly switches to a dramatically different, perhaps catastrophic state. The system may be a power grid that experiences a slow rise in demand, leading to a large-scale power outage, or a climate system, subject to increasing greenhouse gases, that has an abrupt shift in mean temperature. For a system with multiple potential outcomes, Takashi Nishikawa (Northwestern University) and Edward Ott (University of Maryland) report that it may be possible to steer the system to a desirable outcome by giving it a small, carefully chosen push. They theoretically consider the evolution of a noisy one-dimensional system: At each iteration, the current position is mapped to a new position, where the mapping depends on a slowly varying parameter plus some random noise. When the parameter reaches a threshold value—a...

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