Does the entropy of a closed system always increase

In summary, the question asks if the entropy of a closed system always increases, and the answer is that according to the laws of thermodynamics, it will tend to increase. However, there are rare cases where entropy can decrease, such as with a small enough system or with the help of gravity. This phenomenon is statistically possible but highly unlikely. Additionally, thermodynamics is a subset of statistical mechanics where a large enough sample size is assumed to make the 2nd law true.
  • #1
Jeebus
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Question: Does the entropy of a closed system always increase, or could it possibly decrease?

Answer: The standard answer to your question from the laws of thermodynamics is that entropy (disorder) will increase, but there are at least two ways I believe entropy can decrease in a closed system.


First, you used the word 'possibly'. The laws of probability allow a closed system's entropy to decrease, but with such a low likelihood that the odds would make it very unlikely. Making the system small enough, however, by decreasing the number of its possible states can help improve the odds.


Take, for example, a movie of a billiards game 'break' shot. The ordered arrangement of balls becomes disordered, but running the film in reverse would show each individual collision obeying the usual physical laws. The time reversal would be apparent, however, when all the balls ended up in an ordered collection. Although that result could conceivably occur by chance, it is very unlikely. Reducing the example to just two balls would make the odds of an orderly arrangement occurring more likely.


For a second example of decreasing entropy, start with a closed system large enough to allow significant gravitational forces among its components. Gravity provides a 'negative energy' that can take a completely disordered system and organize it into a radically symmetric arrangement around a common center of gravity.



Follow-up Question to above Answer: Regarding the above example of the 2nd law and gravity "organizing" the balls...In that case, wouldn't the balls be in a non-equilibrium state to begin with, since it allows for seemingly automatic movement of the balls? That would mean that not all the conditions for 2LOT have been fulfilled and it would not be a great surprise to see some end-state of organization, right?
 
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  • #2
You are right staiscally it is possible in any closed system for entropy to increase, indeed on very small scales, over short time periods this has been observed. Note the second law really should say 'tend' to increase rather than 'will' increase' at is a staistcal process.

Gravity is no way to combat entropy, your forgetting the GPE lost by objects as the fall towards mass.
 
  • #4
So first one is right, second is wrong. But hey, that first one was pretty darn good - its essentially a logical proof of the Heisenberg Uncertainty Principle.
 
  • #5
Thermodynamics is a subset of the field Statistical Mechanics. It is implicit in the field that sample sizes will be sufficiently large to essentially disregard that which is statistically insignificant. By applying the 2nd law of thermodynamics, a large enough sample size is assumed to make it true. Otherwise, you really have a "many-body" problem, in which you must solve for each individual body's state.

Njorl
 
  • #6
Originally posted by Njorl
Thermodynamics is a subset of the field Statistical Mechanics. It is implicit in the field that sample sizes will be sufficiently large to essentially disregard that which is statistically insignificant. By applying the 2nd law of thermodynamics, a large enough sample size is assumed to make it true. Otherwise, you really have a "many-body" problem, in which you must solve for each individual body's state.

Njorl


Ok. Thanks for the insight.
 

1. Does the entropy of a closed system always increase?

The second law of thermodynamics states that the total entropy of a closed system will always increase over time. This means that the disorder or randomness within the system will tend to increase, and it is highly unlikely for the entropy to decrease spontaneously.

2. What factors affect the change in entropy of a closed system?

The change in entropy of a closed system is affected by the amount of energy transferred, the temperature, and the physical properties of the system. For example, when energy is added to a system, it can increase the disorder and thus increase the entropy.

3. Can the entropy of a closed system decrease temporarily?

While it is highly unlikely for the entropy of a closed system to decrease spontaneously, it is possible for it to decrease temporarily. This can occur when energy is added to the system and it becomes more ordered, but eventually, the entropy will increase again.

4. Is there a limit to how much the entropy of a closed system can increase?

There is no limit to how much the entropy of a closed system can increase. As long as there is energy being transferred and processes occurring within the system, the entropy will continue to increase. However, there may be limits to how much the entropy can change in a specific amount of time.

5. How is the concept of entropy related to the concept of disorder?

Entropy is a measure of the disorder or randomness within a system. As the disorder increases, so does the entropy. This means that a highly ordered system will have low entropy, while a disordered system will have high entropy. The second law of thermodynamics states that the total entropy of a closed system will always tend to increase over time, meaning that the disorder within the system will also tend to increase.

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