What does the concept of entropy mean?
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Imagine you tidy up your room, over time it gets messy. It will never go back to it’s initial tidy state on it’s own. It will always get more messy. So you have to clean it to bring it back to its tidy state.
Same applies to physical systems. Assume you have a perfectly ordered system, over time, it loses it’s order slowly. It will never move itself back to the perfectly ordered state. It will always drift towards no order.
That’s entropy.
At a high level, entropy is a measure of randomness. What it really means is how many different ways can the parts of something be arranged while still looking the same as a whole.
For example, if you have a ball pit, but sort all of the balls into clumps of each color, ie all the red ones in the top left, all the blue ones in the top right etc. there are only so many ways you can rearrange the balls in that pit until a casual observer can tell that someone came by and changed the arrangement in the ball pit.
If you have the balls all mixed together, there are more ways you can shuffle the balls before an observer can tell that the arrangement was changed, meaning it has a higher entropy.
In the field of thermodynamics, we would be talking about the arrangement of atoms and molecules, and what we would be observing would be things like temperature, and density. Even though the molecules in a glass of water are constantly moving around and breaking apart and coming together, from our perspective all of these different arrangements are effectively the same overall system to us since bulk properties like the temperature and density are still the same.
They explain this well in “tenet”. I would recomend you to watch it. Or maybe I misunderstood the question.
So. This is from my viewpoint.
It’s the karmatic wheel. What goes around comes around.
There is order and chaos. Good and evil.
Fate and fortune along with misguided and mislead.
Imagine you’re telling me what your room looked like so I can perfectly replicate it. Entropy is roughly the number of words it’ll take for you to describe your room, in all details, to me. If your room is clean, it takes fewer words to describe. If your room is messy, more words. That’s a very technical definition of entropy that’s nonetheless eli5 hopefully.
I would like to re-ask this question to get an answer that could be explained to a five-year-old. One of the responses mentions that this is likely not possible. If that’s true, so be it.
I was taught the answer is, “The center does not hold.” Everything gets a little more complicated the further in time we go. None of the answers sound anything like this, so I’m assuming what I was taught was wrong.
Sooo, can someone actually ELI5?
Several good examples here from the perspective of orderliness. But is it possible to describe entropy from the perspective of energy states before and after a natural phenomenon?
It depends on who you ask. Ask an engineer who deals with thermodynamics you get a totally different answer to a physicist. When I had a thermodynamics course as part of my engineering degree we had one lesson dedicated ONLY to the concept of the term and discussion of it. Afterwards he had a rule about not talking about it, and just going with the terms of the equation.
In engineering entropy means that the potential difference changes. A bucket of ice in a room. As the ice melts it “takes energy” from the room. The entropy of the room decreased, but the entropy of the bucket has increased. If you consider the room and everything in it as one system, there has been no change in entropy.
While a physicist might say that increase in entropy means that structured or ordered system becomes more random.
If you ask an IT person, to them entropy means the amount of information a message is missing.
Others have pointed out that it is a measure of the order/disorder in a system. But I think that is not quite getting to the point.
The point is that it is a way to know how much work can be done in a closed system.
First, it is easy to misunderstand “closed system”. This is a concept of an isolated hunk of stuff where nothing comes in, and nothing goes out. Well, there is no such thing other than (arguably) the entire universe.
For example, the Earth is sitting in space, not touching anything, but is not closed because energy comes from the sun as radiation particles. And the Earth radiates lower heat energy, and has particles stripped away.
So this is more of a thought experiment, and in practice, a way to find inputs to a system when those inputs may not be obvious.
So… As a thought experiment: if you make a closed system out of the earth, then the plant life will all die from lack of light, then everything else will die in a chain reaction. That is not the interesting bit. Over time, the crust of the Earth would heat up and melt. Why? In Earth’s current state, the core is the hottest due to several processes, and the crust is cool because it is able to radiate heat to space. In a “closed system Earth”, Earth can no longer radiate out heat, so the entire Earth becomes the same temperature over time. And that temperature is high enough to melt the crust.
This is more interesting than it might seem at first. Most power generation has to do with temperature differences. The simple example is a steam engine. It is the concentrated heat on one side that provides the energy. In our “closed system Earth”, one the heat has equalized, there is much less opportunity to create such engines. The Earth would be in a higher entropy state. Less work can be accomplished.
In the real world, we can literally dump water into a deep hole, have earth heat the water to steam, and use the steam to run a generator. This is a lower entropy state. More work can be accomplished.
I think Brian Cox has good explanation in one of his shows.
If you build a sand castle is a desert it as highly ordered structure (low entropy) but over time it will revert back to just grains of sand (high entropy).
However over the the time the desert has existed the sand has never been randomly arranged as a sand castle. It is not impossible just very unlikely that would happen because naturally thing seems to go from low to high entropy.
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