Entropy is not just disorder, but a measure of information

Science · Published 25 October 2026 Swipe more like this →

In short: We often think of entropy as the universe's slide into chaos, the reason time only moves forward. But modern physics suggests something deeper: entropy is actually tied to information itself. To understand why things fall apart, we have to look at how much data it takes to describe them.

The second law of thermodynamics states that entropy in an isolated system always increases, which provides the primary physical explanation for the forward flow of time. Traditionally, this was visualized as a transition from order to disorder. For example, when gas expands into a larger container, it occupies more possible arrangements. While it is statistically possible for those molecules to spontaneously cluster back into one half of the container, the odds are so infinitesimal—roughly one in 10 followed by 30 sextillion—that it is considered statistically impossible.

This concept was famously challenged by James Clerk Maxwell's 'demon,' a thought experiment where a tiny entity sorts fast and slow molecules to decrease entropy without doing work. For over a century, this seemed to break the laws of physics. However, researchers at IBM eventually resolved the paradox by identifying the missing link: information. They demonstrated that for the demon to sort the molecules, it must gather data about their movements, effectively building a memory record.

Physicists Rolf Landauer and Charles Bennett proved that this accumulation of information is itself an increase in entropy. The decrease in physical disorder is perfectly offset by the growth of information within the demon's 'brain.' Furthermore, they established that erasing this information produces heat, further increasing entropy. Ultimately, entropy serves as a measure of the information required to express a system's microstates; high-entropy systems simply require more data to describe.

This shift in perspective is profound because almost all physical laws are time-reversible. The second law stands out as an exception primarily because it links the physical state of matter to the informational limits of the universe.

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