As far as I interpret it, the law of ever increasing entropy states that "a system...

As far as I interpret it, the law of ever increasing entropy states that "a system will always move towards the most disordered state, never in the other direction".

Now, I understand why it would be virtually impossible for a system to decrease it's entropy, just as it is virtually impossible for me to solve a Rubik's cube by making random twists. However the (ever so small) probability remains.

Why does this law underpin so much of modern physics? Why is a theory that breaks this law useless, and why was Maxwell's demon such a problem? Does this law not just describe what is most likely to happen in complex systems, not what has to happen in all systems?

Solutions

Expert Solution

Hannesh, you are correct that the second law of thermodynamics only describes what is most likely to happen in macroscopic systems, rather than what has to happen. It is true that a system may spontaneously decrease its entropy over some time period, with a small but non-zero probability. However, the probability of this happening over and over again tends to zero over long times, so is completely impossible in the limit of very long times.

This is quite different from Maxwell's demon. Maxwell's demon was a significant problem because it seemed that an intelligent being (or more generally any computer) capable of making very precise measurements could continuously decrease the entropy of, say, a box containing gas molecules. For anyone who doesn't know the problem, this entropy decrease could be produced via a partitioning wall with a small window that the demon can open or close with negligible work input. The demon allows only fast-moving molecules to pass one way, and slow-moving ones the other way. This effectively causes heat to flow from a cold body of gas on one side of the partition to a hot body of gas on the other side. Since this demon could be a macroscopic system, you then have a closed thermodynamical system that can deterministically decrease its entropy to as little as possible, and maintain it there for as long as it likes. This is a clear violation of the second law, because the system does not ever tend to thermodynamic equilibrium.

The resolution, as you may know, is that the demon has to temporarily store information about the gas particles' positions and velocities in order to perform its fiendish work. If the demon is not infinite, then it must eventually delete this information to make room for more, so it can continue decreasing the entropy of the gas. Deleting this information increases the entropy of the system by just enough to counteract the cooling action of the demon, by Landauer's principle. This was first shown by Charles Bennett, I believe. The point is that even though living beings may appear to temporarily decrease the entropy of the universe, the second law always catches up with you in the end.

genius_generous answered 1 year ago

Next > < Previous

Related Solutions

The law of entropy can also be called the law of increasing disorder; but this law...

The law of entropy can also be called the law of increasing disorder; but this law seems to contradict the existence of living organisms that are able to organize chemicals into organic molecules. Explain how living things seem to be able to defy the laws of thermodynamics in terms of the universe's entropy due to life processes and the entropy within a living organism. Comment just says "a"...?

So the 3rd Law of Thermodynamics states: the entropy of a system approaches a constant value...

So the 3rd Law of Thermodynamics states: the entropy of a system approaches a constant value as the temperature approaches absolute zero. My question is: What is the constant value?

Does the change in entropy in a system depends on initial and final states of the...

Does the change in entropy in a system depends on initial and final states of the system and the path taken from one state to another

Explain what entropy is and how the entropy of the universe is always increasing and how...

Explain what entropy is and how the entropy of the universe is always increasing and how it takes energy to decrease the entropy of a system.

Interpret the role that common law has played in health care in the United States. Assess...

Interpret the role that common law has played in health care in the United States. Assess the level at which common law has impacted overall decisions related to healthcare policy. Provide two (2) specific examples to support your rationale. Differentiate between checks and balances in the separation of power. Specify two (2) examples related to health care from your state government in Georgia.

Qualitative Predictions about Entropy Entropy is the randomness of a system. At the molecular level, entropy...

Qualitative Predictions about Entropy Entropy is the randomness of a system. At the molecular level, entropy can be described in terms of the possible number of different arrangements of particle positions and energies, called microstates. The more microstates the system has, the greater its entropy. Microstates depend on molecular motion. Molecules may undergo three different types of motion: translational motion, vibrational motion, and rotational motion. During translational motion, the entire molecule moves in one direction. During vibrational motion, atoms in...

Question