Viewing the Universe through 1/f Fluctuations: Solar and Stellar Activity and Unpredictable Change

Nature is full of "fluctuations" that are neither regular periodic motion nor completely random. A representative example is 1/f fluctuation (1/f noise). In this talk, starting from familiar phenomena, I will introduce how fluctuations can be analyzed by decomposing them into frequency components, and then extend the discussion to astrophysical phenomena such as the magnetic activity of the Sun and other stars and magnetic polarity reversals. Furthermore, by comparing these phenomena with models of nonlinear dynamics and synchronization, I will explore what common physics may be hidden behind such complex variability.