What Is Entropy?
Entropy is a measure of disorder or randomness in a system. It's one of the most profound concepts in physics, explaining everything from why ice melts to why we age.
The Second Law of Thermodynamics
The second law states that in any isolated system, entropy always increases or stays the same — it never decreases on its own.
- Hot coffee cools down (never spontaneously heats up)
- Rooms get messy (never spontaneously clean themselves)
- Eggs break but don't unbreak
Entropy and Probability
Imagine a box of gas molecules. There are vastly more ways for molecules to be spread out randomly than clumped in one corner.
High entropy = many possible arrangements (likely)
Low entropy = few possible arrangements (unlikely)
Systems naturally evolve toward more probable states — higher entropy.
The Arrow of Time
Entropy gives time its direction. The past has lower entropy than the future. This is why we remember yesterday but not tomorrow.
The Big Bang started with extremely low entropy. Ever since, the universe has been "running down" toward higher entropy — this process defines time's flow.
Entropy in Daily Life
Your body constantly fights entropy by consuming food (low entropy) and releasing heat (high entropy). Death is when this fight ends.
Refrigerators decrease entropy locally by pumping heat outside — but total entropy still increases.
Information has entropy too. A shuffled deck has higher entropy than a sorted one.
Heat Death of the Universe
If entropy always increases, the universe will eventually reach maximum entropy — a state called "heat death" where nothing interesting can happen. No stars, no life, just uniform temperature everywhere.
This won't occur for 10^100 years or more.
Why It Matters
- Why perpetual motion machines are impossible
- Why energy efficiency has limits
- Why time flows one direction
- Why the universe had a beginning
Entropy isn't just about physics — it's about the fundamental nature of change itself.
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