RPM, path of chance, entropy rituals

[malloyd]

[QUOTE=baronopium;1933591]
how does the perpetual motion machine work by keeping heat on two different sides of the same metal bar?

A perpetual motion machine of the first class violates the first law of thermodynamics - it creates energy from nothing. A perpetual motion machine of the second class violates the second law - it doesn't create energy, but it does allow you to turn heat back into higher quality energy.

If you have a bar that is hot on one end and cold on the other you can run a generator on it - you can boil water on the hot end, expand it through a turbine, condense it on the cold end and repeat. In reality, this will eventually bring the two ends to the same temperature (boiling the water will absorb heat, cooling the hot end, condensing the steam will warm the cold end), but if you can force heat to flow from the cold to hot end in the bar (that is, violate the second law) you can counter that, the two ends of the bar remain at different temperatures regardless of how many times you cycle the water.

can someone explain the reversing an irreversible process concept more thoroughly?

These are technical terms in thermodynamics having to do with whether or not entropy changes as some thermodynamic variable does. In a reversible process you can undo the process and everything in the universe is the same as before you started. Imagine for example compressing an ideal spring. Ease off compressing it and it returns to its starting shape, and the energy it releases as it re-expands is exactly as much as the energy you put into compressing it in the first place. In irreversible process does not do that. If you want to return everything to its original condition, you need more energy than the system has left in it. Imagine a non-ideal spring that has set while compressed - ease off of it and it only returns part way to its original length. Some of the energy you used to compress it has turned into something from which you can't get it back.

how does entropy interact with data?

There are definitions of entropy which relate it to the logarithm of the number of microstates the system could be in that would display the same thermodynamic variables. If you have a bit of data, you have at least one microstate that *can't* be in a different state that it currently is, if it were, the data would be erased. Therefore the more data something contains, the lower its entropy has to be. This line of thinking arises from the Maxwell's Demon thought experiment - it's the entropy reduction inherent in the demon *knowing* if a molecule is fast or slow and thus whether or not to open the stopcock that ends up defeating the scheme.

can you explain why this would be true?

If you can unburn a letter, you could burn it as fuel for a steam engine, unburn it, and burn it again.... You can't unburn something by *just* changing the entropy, the unburning needs to reabsorb the heat burning it generated, so you have to supply heat too.