ELI5-What is entropy?
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It’s the number of ways to arrange the components of something to get the same end result.
An end result that can only be achieved with relatively few combinations of individual pieces is low entropy. An end result that can be achieved with many different combinations of individual pieces is high entropy.
If the end result is that a collection of particles have a certain total energy, then that’s a high entropy state because there are many ways to assign positions and velocities to the particles to get the same total energy.
If the end result is that a collection of particles form an ice cube, that’s a lower entropy state because there are far fewer ways to arrange particles in an ice cube than in a puddle of water.
High entropy states tend to occur in nature because, by definition, there are more ways for them to occur.
entropy measures the video quality of a television
the higher the definition the lower the entropy
4k: low entropy
SD: mid entropy
barely visible midnight cable movies in the 90’s: high entropy
Here is a simple way to understand it. If you have a pair of dice, there are six combinations that give a total roll of seven, but only one combination gives a twelve. If you imagine that you can only observe the sum of the two dice and not the numbers on the individual dice, you have a nice approximation of macrostates, which are observable, and microstates, which contain hidden information that, together, nonetheless are ultimately responsible for the observation you make. Entropy in thermodynamics is kind of a measure of hidden information. The total roll is the macrostate, the numbers on the individual dice are microstates. Seven has the highest entropy, since a roll of seven doesn’t tell you as much about the individual dice, two and twelve have the lowest entropy, since these configurations are very informative about the individual dice.
You know how when you drop a flower vase and it breaks? and if you drop the big pieces, they break. But, if you pick it all up and drop it, it never turns back into a vase? That’s entropy. The universal desire for things to become more and more unorganized.
Many of the analogies people provide are misleading. The example of cleaning a room requires input energy to get it to an “organized” state. However you could spend the same amount of energy to trash a room. What we as humans consider organized or not is completely arbitrary as far as the universe is concerned.
Entropy is inversely related to the energy in a system. High entropy therefore means low energy. Low energy equals low heat. As the universe moves toward increasing entropy, it will eventually suffer a heat death, meaning no heat will exist.
A good way to describe Entropy is with Dice.
If you have a pair of six sided dice, there is only one way you can get a sum of two: by rolling a one on each die.
Conversely, there are 35 ways to not roll a two.
Entropy is the ability for a pair of dice to roll any number available to it, in contrast to its ability to roll a select number.
A coin flip has two outcomes. It has one bit of entropy, as the result can go one of two ways.
Spaghetti on a plate though? Bazillion ways for it to sit there. Such a system has much higher entropy.
I can’t believe no one answered in song:
(Yes, the song literally explains what entropy is. To the tune of OPP by Naughty by Nature. By MC Hawking)
Some of the best lyrics:
*You ever drop an egg, and on the floor you see it break?*
*You go and get a mop so you can clean up your mistake*
*But did you ever stop to ponder why we know it’s true*
*If you drop a broken egg you will not get an egg that’s new?*
Imagine you have a big box of Legos. If all the Legos are the same color and shape, it’s easy to know what you have, right? There isn’t much surprise when you pull out a Lego piece because they’re all the same. This is like having low entropy – everything is very ordered and predictable.
But what if you have a box with many different colors and shapes of Legos? Now, every time you pull out a piece, it could be a surprise! You might get a red block, a blue wheel, or a yellow figure. This box has high entropy – it’s more disordered and unpredictable.
In physics, entropy is kind of like the Lego example. It’s a way to talk about how mixed up or unpredictable things might be in a certain situation. If things are really mixed up (like the box with all different Legos), we say it has high entropy. If things are very orderly and predictable (like the box with all the same Legos), it has low entropy.
And just like you might like to keep mixing up your Lego pieces to build new and different things, in nature, things tend to go from order to disorder. This is often what we mean when we talk about the ‘increase of entropy’ – things naturally get more mixed up over time.
In your childhood home your bedroom has the air conditioner vents open. Your brother in his room has the vents close. There is a door between your two rooms which is shut. The AC system then gives out and stops working
At this point the cold air is in your room and the hot air in your brother’s room. The hot and cold air are orderly separated. The door between your rooms is opened.
Initially your room is still very cold and your brother’s hot. But over time the hot air comes into your room and the cold air goes to brother’s room. The mix of cold air/hot air increases over time.
It does not go back (on its own) to having all the hot air in one room and the cold air in another. This is entropy.
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