The Case For A Thermodynamic Demon - Maxwell's Demon

Some of us think of demons as evil spirits, some think of them as agents of the devil but there are those of us that see them as useful entities to probe our scientific beliefs. In this article we would be looking at one of them.

Source

In 1867, James Clerk Maxwell, a pioneering physicist of the 19th century, introduced a thought experiment that continues to intrigue scientists and philosophers alike. This thought experiment challenges our understanding of the second law of thermodynamics, which states that the total entropy, or disorder, of an isolated system will never decrease over time. The thought experiment is called "Maxwell's Demon", mainly because it introduces a mythical creature with a very special ability and presumed to be a demon. The thought experiment seems to violate the second law of thermodynamic by suggesting that it’s possible to decrease entropy without expending work, leading to a re-examination of thermodynamic laws and information theory.

The second law of thermodynamics states that in an isolated system, entropy tends to increase. Entropy is often understood as a measure of disorder or randomness, and the law implies that natural processes tend to move towards greater disorder. From one interpretation, when the temperature increases, entropy increases. One would like to think that when temperature decreases, entropy should also decrease but that is getting the whole idea wrong, looking at entropy in terms of only temperature is just a piece of the whole process. When you remove a hot pot from the fire and leave it exposed to the environment, naturally it would cool. Because the pot cools (drops in temperature) doesn't mean the entropy decreases, the temperature of the environment is also increasing and entropy comes into play from the overall setup (hot pot + environment). From the overall setup there's a net increase in entropy (increase in random mix of high and cold temperatures) till it gets to a maximum - the equilibrium point where the temperatures have been evenly distributed.

Maxwell’s Demon challenges this principle because it seems to allow for the spontaneous creation of order from disorder, a clear decrease in entropy without any work done.

The Thought Experiment

Maxwell's Demon envisions a container of gas divided into two parts by a partition/wall with a small door controlled by a hypothetical entity — the "demon". This demon operates the door such that it only allows fast-moving molecules pass to one side of the containe, while slow-moving molecules are kept on the other side. Over time, this results in one side of the container becoming warmer (the faster molecules) and the other side cooler (slower molecules). From our pot scenario, there's a wall between the pot and it's environment (when both are in equilibrium), the environment in this case would be air and the wall has a door that is operated by this demon. The demon can observe which of the air molecules has high or low temperature (something we macroscopic entities can't do), the ones with high temperatures it sends them to the pot and those with low temperatures remains in or are sent back (after interacting with the pot) to the environment. This separation seems to decrease the entropy of the system because it creates a temperature gradient without any apparent work/energy input and this temperature gradient can be used to perform external work, thus contradicting the second law of thermodynamics.

One of the consequences of the second law of thermodynamics is that you can never observe a pot in equilibrium with it's environment spontaneously become hot. For the pot to get hot or environment get cooler from our everyday experiences, some form of work needs to be done (possibly by an external agent) to extract heat from the environment. This doesn't mean that the entropy would decrease, in fact, the introduction of extra work through the external agent merely extends the system (pot + environment + external agent), the agent interacts directly with one of them (pot or environment). For example, the external agent can be a fire that heats the air and the air in turn heats the pot. In Maxwell's demon thought experiment, the demon isn't interacting directly with any of the components, it's just controlling the door. If the demon were to carry the molecules to the desired destinations with it's body, then we can say that the extra work/energy came from the demon's motion but that wasn't the case. The paradox/contradiction here from another perspective is that the demon somehow was able to create extra energy (through temperature gradient) out of nothing.

The Resolution: Information Theory

This paradox baffled physicists for years until the advent of information theory in the 20th century by Claude Shannon, it was from here that the link between information and entropy was first spotted. The resolution to Maxwell's Demon’s paradox lies in understanding the role of information and computation, and it's link with entropy/thermodynamics. The later work of physicists and information theorists, notably including figures like Léon Brillouin, Rolf Landauer, and Charles Bennett, has demonstrated that while the demon appears to create order without work, it (the demon) actually requires information processing.

Landauer’s principle, established in the 1960s, provides a crucial insight: the act of erasing or making decisions involves an increase in entropy. The demon, to operate its door, must gather and process information about the molecule's velocities, and the act of recording and erasing this information (to create space for more records) inevitably leads to an increase in entropy. Thus, the demon’s operations are not a violation of the second law of thermodynamics but rather an example of how information processing and entropy are interrelated. These theories seems to be suggesting information is actually a physical thing, experiments have shown that information can be converted to energy (heat) and it would imply that the extra energy came not from nothing but from the demon's computation or information processing.

Implications for Modern Physics

Maxwell's Demon has profound implications beyond thermodynamics, extending into fields such as information theory and quantum mechanics. It underscores the concept that information itself has physical significance. For example, the link between information processing and thermodynamics has influenced the development of quantum computing and nanotechnology. Understanding the thermodynamic cost of information processing is crucial in designing efficient computational systems and advanced technologies.

The Broader Impact

Maxwell's Demon also serves as a philosophical and educational tool, stimulating discussions about the nature of physical laws and the concept of equilibrium. It prompts us to question how we understand and define concepts such as work, energy, and entropy. By dissecting this thought experiment, scientists and engineers are pushed to refine their theoretical frameworks and develop new technologies that account for the subtleties of thermodynamics and information.

Conclusion

Maxwell's Demon remains a seminal thought experiment in the study of thermodynamics and information theory. Although it initially seemed to challenge the inviolable second law of thermodynamics, the resolution through information theory highlights the deep connection between entropy and information. The demon's paradox not only enriches our understanding of physical laws but also drives advancements in technology and theoretical physics. As we continue to explore the interplay between information and physical systems, Maxwell’s Demon will undoubtedly remain a cornerstone in the discussion of entropy and the fundamental principles governing our universe.

For further reading

Maxwell's demon

How Maxwell’s Demon Continues to Startle Scientists

Second law of thermodynamics

Thank you all once again for stopping by to read my jargons and also thank you @stemng, @lemouth and the @Steemstem team for your valuable supports.

Source

Lastly, please don't forget to do the needful
Upvote
Comment
Reblog
If you enjoyed my jargons.

Background image source by @doze