Hello Dragoljub,

I do not know why technical people are so fond of demons, but let me add a few other demon examples. Schrödinger 's cat, which is used to express the superposition of states, could be considered a demon, though it is not formally given that name. In economics, there is statiscian Maurice Kendall's "Demon of Chance" (circa 1953), which he used to explain the absence of serial correlation as measured by the sliding autocorrelation function of commodity prices such as the time series of weekly wheat or cotton prices. For a discussion of Kendall's Demon, see the following book.

Donald MacKenzie; An Engine, Not a Camera, How Financial Models Shape Markets; MIT Press; 2006; pp. 61-63.

There is also the example of an enormous number of monkeys in a room, each sitting in front of a typewriter and typing furiously. The idea here is that this cohort of simian writers could eventually reproduce the play Hamlet. I believe this demon example, though, again, it is not formally designated as a demon, was supposed to represent Boltzmann's idea, from statistical mechanics, that a possible state of gas molecules in a box would be for them to all colalese into one corner of the box. According to Boltzmann such a trajectory, while unlikely, still has a small but non-zero probability.

My last demon example is Murphy's law, which, and I am paraphrasing here, says that, "Anything that can go wrong will go wrong, and usually at the most inopportune time." As a child, I remember seeing the old Warner Brothers cartoon titled "Falling Hare" (circa 1943) with Bugs Bunny and the Gremlin (a.k.a., demon). This particular demon was the root cause of mechanical and electrical problems at a US Army Air Corps (forerunner of the US Air Force) base during WWII, see https://www.youtube.com/watch?v=ZElJxTCIsJI .

I am sure there are more demon examples out there, somewhere.

Regards,

Tom Cuff

Hello Dragoljub,

I really like your question and since no one else is offering up an opinion, let me try.

Demons are entities with a very limited repertoire of skills, i.e., they are the idiot savants of the scientific, engineering, computer science, economic, psychologic, religious, etc. disciplines. For instance, Maxwell's Demon is only good at separating gas molecules based on their velocity (speed + direction). In computer science, small bit code with very circumscribed duties are called 'daemons' in the UNIX operating system. And, of course, reglions and behaviorists speak of bad demons (the Devil and company) and good demons (God and the angels), when trying to understand the question of why there is evil in the world. That angels have specialized functions, such as the Archangels, who are God's hitmen or is it hitwomen (gender ambiguity), has been part of Biblical lore for a long time.

But do these entities actually help explain the world to us, or are they simply concepts within which to hide our ignorance? Some people say that demons are simply strawpersons, who can be dispatched to oblivion and beyond if we think about the problem they represent long enough, i.e., they are created to be knocked down. Most demons appear to be part and parcel of the classical world view as opposed to the quantum world view. This is true even of Schrödinger 's cat , which is a macroscopic manifestation of the measurement problem. Thus, demons appear to be a holdover from the mechanistic ideas of classical mechanics if you will. One usually does not hear of demons in quantum mechanics because one simply solves the appropriate wave equation and whatever it says - no matter how incomprehensible - is what happens, i.e., there is no causality, hence, there is no need of demons to serve as the antecedent to subsequent behavior.

Regards,

Tom Cuff

Thank you Mr Thomas Cuff for your very useful answers.

Hi Dragoljub,

as a supplement to Tom's answers, I feel that demons like Maxwell's are intended to answer the question:

Is a certain limitation based on a general law of nature or just a consequence of (perhaps temporal) human lack of knowledge or of ability?

A demon has strictly to comply with the laws of nature in order to be useful; but otherwise it can be as small or large, as fast, as strong and as smart as it benefits its inventor, i. e. it has superhuman but no magical skills.

Some decades before the introduction of light quanta, Maxwell's demon can "see" atoms in any dim light. So from Maxwell's point of view, humans might never be able to decrease the entropy of an isolated system but if they could it wouldn't violate a natural law, i. e. the 2nd law of thermodynamics isn't a "general" law.

I seem to remember that Heisenberg once explained his uncertainty principle by illustrating the impossibility of measuring both the position and the momentum of a particle exactly, but I think the general consensus of the Kopenhagen school was (or is) that a particle hasn't exact position and momentum simultaneously. By taking this standpoint, they answered the above question at the outset, rendering all demons in the realm of quantum mechanics unemployed.

I wouldn't count Schrödinger's cat among the demons because it doesn't answer the above question, and it is no agent; its strength, its speed, and its intelligence doesn't matter at all. Indeed (it's just a thought experiment, after all!) one could replace the cat by any human without altering the point of the experiment but this replacement would cause revulsion beyond the group of cat lovers.

PS This last point reminds me of the question whether the human who opens the box must have a physics diploma in order to qualify as "observer". :-) In my opinion, the cat is no worse observer than any human; so the thought experiment fails in any case.

Back to your original question, yes, I think that thought experiments employing demons - as well as those without them - can contribute to a better understanding. While a theory is best tested by experiments, it should be able to withstand any reasonable "attack" by demons, too. A failure indicates a weak point, either in the theory or in the construction of the demon.

Hello Dragoljub,

Joerg has mentioned some interesting points, but there are some things he states with which I have to disagree. The Second Law of thermodynamics is as far as I can tell a general law. It is as universal in its applicability as the First Law of thermodynamics. Quantum mechanics, which borrows very little from classical physics, nevertheless, adheres to the First Law of thermodynamics. In fact, Schrödinger 's wave equation is an explicit statement of the conservation of energy (First Law) in the sense that kinetic plus potential energy equals the total energy of the particle/wave under consideration. As far as the Second Law is concerned, quantum physicists have sought not to violate this law. In fact, it hard to understand how violating the principal laws of thermodynamics at the microscopic scale would not spill into the macroscopic world.

It is ironic that quantum mechanics, which is concerned with the behavior of the very small, such as elementary particles, atoms, molecules, etc. should strive not to violate the principal laws of thermodynamics. Thermodynamics was discovered before scientists knew or widely believed in atoms or molecules. People forget that Max Planck, the Father of quantum physics, was a doyen of thermodynamics, and he only reluctantly adopted Ludwig Boltzman's atomist view of matter.

The reason I believe Schrödinger 's cat is a demon is because the cat is an idealization (thought experiment), just as Maxwell's Demon is an idealization. The cat is assumed to obey the linear wave equation and so its two possible states (dead and alive) are independent solutions, whose linear combination (superposition) is also a solution of the same wave equation. If the flask of HCN gas inside the box housing the cat is broken when the GM tube detects a radioactive decay, a real cat will take an easily measurable time to expire. But quantum mechanics does not speak about the the time it takes for a quantum jump from one state to another or even what is going on during the transition. Therefore, I believe the cat is an idealization meant to illustrate a concept. When the box is opened, the cat must instantaneously assume the position (dead or alive). It must make the transition instantaneously because the very act of observing it collapses its wavefunction to one possible state or the other. Thus, the cat has a very circumscibed set of behaviors. These very limited behaviors might be why Schrödinger 's cat cannot act as its own observer anymore than Maxwell's Demon can act as its own observer.

Regards,

Tom Cuff

Thank you Mr Joerg Fricke for your very inspiration answer.

To Mr. Joerg Fricke and Mr. Thomas Cuff

The Maxwell's demon has shown that under cosmic and microscopic conditions, there are processes that are opposite to the processes in our Earth conditions.

This means that under such conditions it can be reasonably assumed that entropy can decline versus entropy growth in our conditions.Therefore, it can generally be said that under our conditions entropy rise is most probable, entropy constancy is unlikely, and entropy decline is unbelievable.However, the conclusion about the rise of entropy must not be extended to space conditions, as this can lead to absurd conclusions. For example, the conclusion that the entropy of the Universe-which is viewed as a closed system in which irreversible processes take place- tends to its maximum, which will lead to the thermal death of the Universe and the like. Such assumptions ascribe to the Universe our earthly conditions, although today we know that these conditions are not the same, but rather the exact opposite.