Developed in the 1980s and 1990s, this theory proposes that dreams arise out of the brain’s editing and organizing of recent memories. This contrasts with the Freudian theory of dreams as the symbolic expression of forbidden desires. 

The chief insight of Chaos theory is that complex, nonlinear systems display exponentially increasing possible outcomes. This means that, for example, the path of a bubble on a stream depends critically on tiny fluctuations of the stream’s surface around the bubble, which cause the number of possible paths for the bubble to rise so rapidly that it becomes essentially impossible to predict its future location. This also explains why it’s so hard to make accurate predictions about the weather, stock prices, political change, and the decisions of individuals over time. 

Simple systems—atoms, molecules—combine to form complex macromolecules whose structures are nearly impossible to predict from their building blocks. These molecules, in turn, combine to form organelles, cells, tissues, organs, organisms, species, and ecosystems, and at each higher level of complexity appear properties and traits quite unexpected from the simpler levels. These surprises are called emergent properties; they also include such phenomena as technological innovation, the rise of civilizations, and the colors of butterfly wings.