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When meaningful predictions cannot be made, the system appears random. This means, in practice, a meaningful prediction cannot be made over an interval of more than two or three times the Lyapunov time.

Hence, mathematically, doubling the forecast time more than squares the proportional uncertainty in the forecast. In chaotic systems, the uncertainty in a forecast increases exponentially with elapsed time. Some examples of Lyapunov times are: chaotic electrical circuits, about 1 millisecond weather systems, a few days (unproven) the inner solar system, 4 to 5 million years. The amount of time for which the behavior of a chaotic system can be effectively predicted depends on three things: how much uncertainty can be tolerated in the forecast, how accurately its current state can be measured, and a time scale depending on the dynamics of the system, called the Lyapunov time. Chaotic systems are predictable for a while and then 'appear' to become random.

A metaphor for this behavior is that a butterfly flapping its wings in Brazil can cause a tornado in Texas. The butterfly effect, an underlying principle of chaos, describes how a small change in one state of a deterministic nonlinear system can result in large differences in a later state (meaning that there is sensitive dependence on initial conditions).
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Chaos theory states that within the apparent randomness of chaotic complex systems, there are underlying patterns, interconnectedness, constant feedback loops, repetition, self-similarity, fractals, and self-organization. The double-rod pendulum is one of the simplest dynamical systems with chaotic solutions.Ĭhaos theory is an interdisciplinary scientific theory and branch of mathematics focused on underlying patterns and deterministic laws, of dynamical systems, that are highly sensitive to initial conditions, that were once thought to have completely random states of disorder and irregularities. Starting the pendulum from a slightly different initial condition would result in a vastly different trajectory. An animation of a double-rod pendulum at an intermediate energy showing chaotic behavior.
