Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

So I was eating a plate of food one day and thought of entropy. As I understand the definition of entropy, it is the logarithm of the number of arrangements or states the object in question can be in, where the object is composed of N number of particles/food particles. Please edit my definition if this is wrong.

So, I'm eating a plate of food, and I have diced up chicken, rice and vegetables on the plate all mixed together. I thought, the current system I have, the food is arranged in a state that is of high entropy because this arrangement is common compared to the number of other more rare arrangements, ie 1/3 chicken, 1/3 vegetables, and 1/3 rice in an pie chart looking fashion.

I like to eat neatly, and naturally, I've conditioned myself to pick up the food with my fork such that while I pick up chicken and rice, rice falls off one side of my fork in a certain direction. As I eat, I sometimes end up with a more neater, higher entropy state than what I began with. I didn't spend extra energy making it neater, I just pick up my food in strategic ways because that's how I normally eat.

My question is, how is this possible? I end up with a more neat arrangement on my plate than I started with. I know food gets eaten, so the number of particles decreases with time. So because the number of food particles decreases, the number of arrangements also decrease!! Can someone continue my chain of thought and correct me if I'm wrong? What do I need to think of next? Why is it that it appears that the entropy of my plate of food seems to lower with time?

share|cite|improve this question
If I say my baby daughter eating food, I'm pretty sure the entropy of the universe is increasing... – Fabian May 30 '11 at 15:49
up vote 6 down vote accepted

QEntanglement, the answer is simple.

Your plate of food is not a closed system. For the system to close you need the plate, and the whole of you. with your chewing and digestion. Entropy increases in closed systems. Otherwise, think about it, could DNA exist, and the whole caboodle of organic life? We are factories that defy entropy, until we die, because we are open systems.

In inorganic systems, crystals crystallizing out of a solution are highly ordered, but they are not a closed system. When the solution is considered to close the system, entropy increases.

share|cite|improve this answer
Thanks anna! Your just as cool as Luboš Motl. He's my idol. I hope he sees this compliment of him. Now your my idol too. – QEntanglement May 30 '11 at 10:42
@QEntanglement: Although I discourage idolization... he won't see this comment, unless you '@' him on a post he contributed to or got involved with. – JamalS May 12 '14 at 13:45
@JamalS that comment is from 2011 !!! – anna v May 12 '14 at 13:51
@annav: Oops, I didn't realize :) – JamalS May 12 '14 at 13:53

Entropy is the measure of the disorder or randomness in a system. In other words, if you drop a box of matches on the floor, the matches will fall all over the place, which is an increase in entropy. For an example of decreased entropy, if you build a house you are making order, not chaos, so the entropy-the disorder of a system-is decreased. I hope this was an understandable explanation. :)

share|cite|improve this answer

First: Look at the good answer by anna.

One side note: The second law of thermodynamics (increase of entropy) is a stochastical law. That is: It is like this 99.99…% of the time/system you look at. But there might be instances, where it is decreasing for some short time (but very likely will increase shortly after to the values observed at any time before).

Background: Poincaré recurrence theorem basicly states, that a closed system will get back to a point very close to its current state at a later time. This time might be extremely long (so long, you can basicly summarize it as "never"). Zermelo noted (not the best link, but I did not find a better one) that this contradicts increase in entropy. Boltzmann had a lengthy answer paper in 1896 (doi:10.1002/andp.18962930414, it's in german) explaining this and explaining that this is a stochastical thing.

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.