Both of my girls ran to me while Tim stood up and waved his hands at the geyser, happily laughing at the sound and feeling the rush of air that followed the water into the air. The next eruption was right on time, and we left Old Faithful enthralled at the beauty of the spectacle we had just seen. Over the long haul, there will be major changes in the geyser's eruptions as the molten rock that generates the steam to fuel the geyser cools and as tectonic activity changes the vent systems. Being faithful carries an air of uncertainty in the physical world. Even the laws of science predict that eventually all things in the cosmos will fail.
Astronomers talk about heat death when they discuss stars.
Chemists talk about entropy and activation energy when they talk about chemical reactions. Physicists talk about the second law of thermodynamics when they discuss the relationships between work and heat. In recent years, we have even come to understand that the building blocks of atoms can decay. Protons, for example, seem to eventually break down into more fundamental building blocks of matter. Even the shape of space itself can be shown to end in the singularity called a black hole.