The second law of thermodynamics states that in any natural process, the total entropy of an isolated system will either increase or remain the same—it never decreases.

Entropy is a measure of disorder or the number of ways energy can be distributed in a system. As energy spreads out and becomes less organized, entropy increases. This means that over time, systems naturally evolve toward a state of greater randomness or equilibrium.

Examples of this principle include:

• Heat always flows from hotter to cooler objects, not the reverse.
• A broken glass doesn’t spontaneously reassemble—it moves toward a more disordered state.
• In chemical reactions, irreversible processes often increase entropy.

This law explains why perpetual motion machines are impossible and why energy conversions (like in engines) are never 100% efficient—some energy is always lost as unusable heat.

The second law governs everything from thermodynamics and chemistry to the arrow of time in the universe.