Final answer:
Chaos requires systems to be highly sensitive to initial conditions, which leads to unpredictable long-term behavior in various scientific fields.
Step-by-step explanation:
A necessary condition for a system to be chaotic is high sensitivity to initial conditions. This means a very small change in the starting point can lead to drastically different outcomes, making long-term prediction almost impossible.
Numerous systems demonstrate this behavior, including fluid dynamics, planetary orbits, and biological phenomena such as the human heartbeat in certain conditions.