ELI5: What is entropy?

Entropy is a measure of how messy or disordered something is.

Imagine your toys scattered all over your room: that's high entropy. Now, imagine all your toys neatly put away in their boxes: that's low entropy. Entropy in science is similar; it describes how spread out energy and matter are in a system.

Think about it like this:

• Imagine you have a hot cup of cocoa. The heat from the cocoa is concentrated in the cup. That's low entropy for the heat energy.
• Now, if you leave the cocoa out, the heat will spread out into the cooler air of the room. The heat energy is now more spread out and less organized. That's high entropy.

Here's another example:

• You build a perfect sandcastle on the beach. That's a very ordered, low entropy state.
• But the wind and waves will eventually break it down, scattering the sand. The sand is now more spread out and less organized. That's higher entropy.