Can change in entropy be negative?
The short answer is yes, but it’s not as simple as flipping a switch. I know it sounds contradictory at first—how can disorder decrease? But here’s what most people miss: entropy isn’t just about messiness in a room. It’s about the hidden dance of molecules, energy, and probability playing out across systems large and small.
The Real Definition of Entropy
Let’s cut through the confusion. Which means entropy isn’t really about chaos or disorder in the everyday sense. But it’s a measure of how spread out energy becomes—or how many ways a system can be arranged while still looking the same overall. Think of it like this: when you mix sugar into tea, the sugar dissolves and spreads evenly. That’s entropy increasing because the energy (and the sugar molecules) are more dispersed.
But here’s the kicker: entropy can go down in certain parts of a system—even as the whole universe keeps getting more disordered.
Why This Matters
Most people learn that entropy always increases. That’s the second law of thermodynamics, right? But that rule applies to isolated systems—like the entire universe. When we talk about entropy change in a closed system or even an open one (like your body or a fridge), things get more interesting.
Understanding this tells us something powerful: we can create local order. We can cool a drink, grow a crystal, or even organize our bookshelf. But doing so requires energy input—and that energy disperses elsewhere, usually as waste heat.
How Entropy Actually Changes
Let’s break down how entropy change works in practice.
The Formula (But Make It Simple)
ΔS = Q/T
This equation tells us the change in entropy (ΔS) equals the heat added to the system (Q) divided by the temperature (T) at which the transfer happens. But if you add heat to something, its entropy goes up. If you remove heat, it goes down. Simple, right?
But again—it depends on whether you're looking at the system alone or the system plus its surroundings.
Local vs. Global Entropy
Imagine freezing water into ice. Plus, as the water molecules slow down and lock into place, the entropy of the water decreases*. But during that process, heat is pumped out into the environment—usually as waste. There are fewer ways for the molecules to move around. That released heat increases the entropy of the surroundings more* than the decrease in the water.
So locally, entropy went down. Globally, it went up.
This distinction is crucial. Even so, it means yes—entropy can decrease in a subsystem. But only if something else compensates by increasing more.
When Entropy Decreases (Yes, Really)
There are plenty of real-world examples where entropy decreases in a controlled way.
Crystallization
When a solution cools and forms crystals, the molecules settle into an ordered structure. The system becomes more predictable, more organized. So that’s a clear drop in entropy. But again, this only happens because energy (heat) was removed and dispersed elsewhere.
Living Organisms
Your body maintains order by constantly taking in energy—food—and using it to stay organized. You’re more ordered now than when you ate that sandwich. But your metabolism also produces heat and waste, increasing entropy in the environment.
Refrigerators
A fridge pulls heat from inside and dumps it into the kitchen. The air inside becomes cooler and more ordered—lower entropy. But the compressor heats up the back coils, increasing entropy outside.
In each case, something special happens: work is done to move energy from a colder place to a hotter one. That violates the “natural flow” of energy, so it requires input—and pays for it with entropy elsewhere.
What Most People Get Wrong
Here’s where the confusion usually starts.
Entropy Isn’t Always Increasing
People hear “entropy always increases” and apply it to everything. But that law only holds for isolated* systems. On top of that, entropy decreases here. Earth isn’t an isolated system—we get energy from the Sun. So locally, life builds complex structures. But the Sun’s radiation spreads out into space, increasing entropy much more.
Continue exploring with our guides on tin indium silver alloy differential scanning calorimeter and how is density affected by temperature.
Disorder ≠ Entropy
This is huge. Just because something looks messier doesn’t mean its entropy is higher. A gas filling a container has high entropy because the molecules can move in many ways. A pile of papers might look messy, but if they’re all the same weight and shape, their arrangement might not be as probable as you think.
Entropy is about possibility*, not appearance.
You Can’t Beat the Second Law
Some folks think that if entropy can decrease locally, maybe we can cheat the second law entirely. The total entropy of an isolated system never decreases. We can’t. You can create order, sure—but only by exporting disorder.
Practical Tips for Working With Entropy
Want to harness or account for entropy changes in real life? Here’s what actually works.
Understand Your System Boundaries
Ask yourself: am I looking at just the system, or the system plus its environment? If you only count part of the picture, you’ll miss the full entropy story.
Look for Energy Flows
Whenever entropy decreases somewhere, trace where the energy went. That’s usually where the compensating increase happens. In business, tech, or biology, this shows up as waste heat, byproducts, or inefficiencies.
Use Refrigeration and Cooling Wisely
If you want to reduce entropy in a space (like preserving food or making electronics efficient), plan for where the heat goes. Don’t trap it. Let it escape.
Think in Terms of Probability
High entropy means lots of microstates—the hidden arrangements that still look the same macroscopically. Low entropy means fewer arrangements. Day to day, when designing processes, ask: am I reducing possibilities? And at what cost?
FAQ
Can entropy decrease in the universe?
No. The total entropy of the universe always increases or stays the same. But parts of it can decrease—as long as other parts increase more.
Does entropy only apply to physics?
Nope. The concept shows up in information theory, biology, economics, and even sociology. Anytime you’re tracking how spread out or organized something is, you’re dealing with entropy-like ideas.
Can life exist if entropy always increases?
Absolutely. Life thrives by locally decreasing entropy—using energy from food or sunlight. But it also expels entropy as waste, keeping the total increase positive.
Is entropy the same as randomness?
Close, but not quite. Entropy measures the number of possible arrangements that look the same overall. Randomness is one way to achieve that—but not the only one.
Why does ice melting increase entropy?
When ice melts, the molecules gain freedom to move. They go from a rigid lattice to a more fluid state. More movement = more possible arrangements = higher entropy.
The Bigger Picture
So yes—entropy can decrease. In fridges, in living cells, in growing crystals. But every time it does, the price is paid somewhere else.
That’s not a flaw in the universe. So it’s the rule. And it’s also what makes complexity possible. Without the ability to locally reverse entropy, there’d be no stars, no planets, no life.
Understanding entropy changes—whether positive or negative—helps us see the hidden mechanics of everything from weather patterns to computer chips to the rhythm of our own breath.
Entropy isn’t just a physics term. It’s a lens. And once you look through it, you start seeing order and chaos not as opposites, but as partners in an endless exchange.
