Discussion of the 3 thermodynamic laws

What's the minimum number of particles for thermodynamics to 'work'? Also, are you saying that the smaller number of particles in a system the more likely you can do "something contrary to the laws"?thanx
PM1KPS: When you say 'particle', to what object are you refering?

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What's the minimum number of particles for thermodynamics to 'work'?

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As far as I know, 2.

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Also, are you saying that the smaller number of particles in a system the more likely you can do "something contrary to the laws"?

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From my own knowledge of thermodynamics, nothing contrary could happen, but things could be out of equilibrium. It is similar to gambling where you can beat the house in the short term but lose to the house in the long term. Improbable things can happen with fewer particles, but nothing contrary to the actual rules. For instance, even with 2 particles "coldness" can not move from one particle to the other, it is still heat/energy moving between the particles.

You aren't doing something contrary, but you can have trade offs. For example, take a refridgerator. If the room is at a certain temperature, a refridgerator, through the use of work (in compressor) is able to pump the heat out of the refridgerator (making it cooler than the surroundings). Since systems, according to thermodynamic laws, approach equilibrium, this may seem contrary. However, as you make the refrigerator cooler, you expel heat into the surrounding enviroment (1 law, energy conserved). You also have put work into the system (thermodynamic laws are based on closed systems). Finally, you are also increasing the overall entropy of the system (3rd law), since usable work is converted into heat. Thus, upon closer examination, you can understand the refridgerator violates none of the laws. (actually it operates on understanding these very principles, and using them appropratiley)This message has been edited by Darwin Storm, 08-27-2004 01:22 PM

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Thus, upon closer examination, you can understand the refridgerator violates none of the laws.

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Just a quick observation. As a child using child-like logic, you thought that if someone opened up all of the refridgerators world wide that the temperature would drop. However, the truth of the matter is that given enough open refridgerators the global temperature would actually increase in keeping with the thermodynamic laws. This example helped me to better understand laws of thermo when I first studied them.

yep, temp increases since energy is being put in into the system and converted to waste heat.

I like it! I like it alot!Quick questions - Does the amount of waste heat increase as more and more electronic devices are being used? Will this heat become a potential problem at some point in the future?Just wondering
PM1K

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Quick questions - Does the amount of waste heat increase as more and more electronic devices are being used? Will this heat become a potential problem at some point in the future?

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I really doubt it. I would suspect that the heat put off by electronic devices is dwarfed by the heat released in ongoing volcanic eruptions both on the ocean floor and above the water. Also, it takes a huge ongoing nuclear reactor (the sun) to just maintain our current temps. Probably the greatest effect on global temps is due to mechanisms that trap more heat from our main source of heat, namely the greenhouse effect. Also, the earth has experienced large swings in temps and glaciation that had nothing to do with the use of electronic devices.

Violations of the 2cnd law can occur. As someone stated it is a statistical law. The fundamantal laws of physics are invariant under time reversal.

Peeper I would love an example. I have tried to come up with one for a number of years, and cannot. If you have one please post it.

Consider the free expansion of a gas, initially trapped in a small volume, into a larger volume. At equilibrium the gas will uniformly occupy the larger volume. Now reverse the momentum of each gas particle and time and watch the film run backwards. The gas, uniformly distributed in the larger volume, now spontaneously evolves to occupy a smaller volume thus reducing the entropy.

Peeper: Correct me if I am in error, but the smaller volume was never a closed system, and thus the 2nd law does not apply. Assuming the larger volume is a closed system, the 2nd law applies there. So what is happening inside that larger volume while the gas "spontaneously evolves to occupy a smaller volume?" If the film can be "run backwards," there may well be less entropy in the open subsystem (the smaller volume). But what of the whole closed system (the larger volume)? There is another problem, what caused this reversal of momentum of each gas particle? And if it is a reversal of time directly, then how do we aviod breaking causality?

The entire volume is the closed system. Gas is evacuating most of the volume to occupy a smaller portion. The entropy of a system increases as the number of states increases. Since a state is defined in terms of momentum and position, as the volume occupied decreases so does the entropy. Time reversal. Surely, if time is reversed then so is causality, hence the time invariance of the fundamental laws.If you do not adopt a statistical interpretation of the 2cnd law of thermodynamics, you will run into conflict with the fundamental laws of physics which are invariant under time reversal. If a gas can migrate from a small volume into a larger volume, then it is surely probable (though unlikely) that the gas can migrate from the larger volume into the smaller volume. According to kinetic theory, what would prevent it?

Causality is the basis of science. A reversal of time does not imply a reversal of causality. Consider the one directional melting of an ice cube that is placed in a flame. When time is reversed the ice is reformed into the original cube. Why? What process says that it should freeze at all? Even if it does, what process governs the shape being restored to the original cube? Time reversals are a problem that cannot be swept aside.But regardless of whether or not an example exists, the supposed problems caused by the laws (especially the 2nd law) to the theories of evolution are simply that. Supposed. There is no difficulty with the laws of thermodynamics as they apply to evolution. These laws do not rule out evolution. Indeed many readings I have done concerning the problems stem from the fact that the laws are often misrepresented and oversimplified.

If time were reversed, wouldn't that be super-natural?

No one is trying to "sweep aside" time reversal problems. There are no "time reversal problems". The laws of physics are fairly well understood. In fact, the law of equal probability which is the basis of statistical mechanics is a consequence of time reversal symmetry.