Maxwell's Demon

[steve_bank]

In usage Maxwell's demon can refer to an infinitesimally small hypothetical observer.

Maxwell's demon - Wikipedia

en.wikipedia.org

Maxwell's demon is a thought experiment that appears to disprove the second law of thermodynamics. It was proposed by the physicist James Clerk Maxwell in 1867.[1] In his first letter, Maxwell referred to the entity as a "finite being" or a "being who can play a game of skill with the molecules". Lord Kelvin would later call it a "demon".[2]


In the thought experiment, a demon controls a door between two chambers containing gas. As individual gas molecules (or atoms) approach the door, the demon quickly opens and closes the door to allow only fast-moving molecules to pass through in one direction, and only slow-moving molecules to pass through in the other. Because the kinetic temperature of a gas depends on the velocities of its constituent molecules, the demon's actions cause one chamber to warm up and the other to cool down. This would decrease the total entropy of the system, seemingly without applying any work, thereby violating the second law of thermodynamics.


The concept of Maxwell's demon has provoked substantial debate in the philosophy of science and theoretical physics, which continues to the present day. It stimulated work on the relationship between thermodynamics and information theory. Most scientists argue that, on theoretical grounds, no device can violate the second law in this way. Other researchers have implemented forms of Maxwell's demon in experiments, though they all differ from the thought experiment to some extent and none have been shown to violate the second law.

 

[Spacetime Inhabitant]

In usage Maxwell's demon can refer to an infinitesimally small hypothetical observer.

Maxwell's demon - Wikipedia

en.wikipedia.org

Maxwell's demon is a thought experiment that appears to disprove the second law of thermodynamics. It was proposed by the physicist James Clerk Maxwell in 1867.[1] In his first letter, Maxwell referred to the entity as a "finite being" or a "being who can play a game of skill with the molecules". Lord Kelvin would later call it a "demon".[2]


In the thought experiment, a demon controls a door between two chambers containing gas. As individual gas molecules (or atoms) approach the door, the demon quickly opens and closes the door to allow only fast-moving molecules to pass through in one direction, and only slow-moving molecules to pass through in the other. Because the kinetic temperature of a gas depends on the velocities of its constituent molecules, the demon's actions cause one chamber to warm up and the other to cool down. This would decrease the total entropy of the system, seemingly without applying any work, thereby violating the second law of thermodynamics.


The concept of Maxwell's demon has provoked substantial debate in the philosophy of science and theoretical physics, which continues to the present day. It stimulated work on the relationship between thermodynamics and information theory. Most scientists argue that, on theoretical grounds, no device can violate the second law in this way. Other researchers have implemented forms of Maxwell's demon in experiments, though they all differ from the thought experiment to some extent and none have been shown to violate the second law.

GOOGLE QUOTE:
Maxwell's demon is a thought experiment by physicist James Clerk Maxwell in 1867 involving a hypothetical being that sorts fast and slow-moving gas molecules to create a temperature difference and seemingly violate the second law of thermodynamics. The "demon" operates a trapdoor between two compartments of a gas, allowing fast molecules to pass to one side and slow ones to the other, which lowers the total entropy. Modern understanding shows that the demon's actions, particularly the erasure of information about the molecules it observes, require energy and thus increase entropy, so the second law of thermodynamics is not violated.

There is no modern controversy about Maxwell's Demon. It was a thought experiment that was not meant to be taken too seriously. Similarly, many people miss the point about Zeno's paradoxes. Zeno wasn't stupid, he was provoking thought. Another example is King Canute (Cnut), he did not think he could stop the waves; he was showing that he could not do that.

 

[pood]

The second “law” is not really a law (I don’t believe there any laws of physics) but an observation of probabilities. The “law” could be violated but it is overwhelmingly unlikely.

 

[pood]

What we call “laws,” I think, are just descriptive statements of how reality goes. Descriptions have no coercive power. I think the idea of “laws” is a hangover from the belief in a lawgiver, i.e., God.

 

[bilby]

The Second Law of Thermodynamics is an emergent property of particles in aggregate; No single particle has entropy, it is a statistical property only applicable to large numbers of particles, and boils down to "There are far more ways to arrange particles such that they are mixed, than there are to arrange them such that they are separated by reference to some chosen characteristic".

Emergence is a very important concept for understanding reality, and 2LoT is a very good exemplar for emergence, due to its simplicity and its position as an important and fundamental part of physics.

Systems involving large numbers of similar or identical components have system-level properties and behaviours that are meaningless at the component-level.

A gas has entropy, but a particle does not; A population evolves, but an animal does not; A brain thinks, but a neuron does not.

The properties of large systems are, hypothetically, simply the aggregate of all the properties of their components, plus all of the interactions between those components. But in practical terms, it is impossible to understand large systems in this way - you don't need more than a handful of quarks, before modelling the interactive behaviour of all of your particles using QM requires more processing power than could ever be available.

At every level, there are techniques, theories, and tools that allow us to understand and predict the way that systems behave. These techniques, theories, and tools are specific to their own level of complexity, and while we can demonstrate that a low level theory (eg QM) will approximate very well to a higher level theory (eg classical mechanics) when aggregated, attempting to use the lower level theory to understand the higher level behaviours is futile, and attempting to use high level theory to understand more fundamental behaviours is invalid and often nonsensical.

All of this is a very good thing, because access to fundamental knowledge first requires a solid working knowledge of higher level systems - if we needed to understand QM before we could build a steam engine, or to understand crystallography before we could knap flint, we would still be hanging around Olduvai Gorge eating berries.

Trying to understand human behaviour by reference to QM interactions between molecules in a neuron is a doomed and pointless excercise; It's the wrong tool for the job, and is like trying to use a set a watchmakers tools to build a suspension bridge.