Feynman Quotes

Just found a few Richard Feynman quotes (famous physicist for those of you who don't know), they're pretty cool:

"Physics is like sex: sure, it may give some practical results, but that's not why we do it."

"To those who do not know mathematics it is difficult to get across a real feeling as to the beauty, the deepest beauty, of nature. If you want to learn about nature, to appreciate nature, it is necessary to understand the language that she speaks in."


Also: Perpetual Motion Machines.

I've been reading up on these since my thermodynamics lecturer told us about the "Feynman Ratchet", a perpetual motion machine that uses the random collisions of gas molecules on a paddle wheel to turn a shaft, which is allowed to turn only in one direction by a ratchet. Of course it doesn't work, because no perpetual motion machine works, but it's rather tricky to understand why. It took physicists quite a long time to figure out why Feynman's device wouldn't work. From what I've read it mostly involves the ratchet slipping just as frequently as it turns forward.
Its actually quite funny how many people out there on the internet bag out physicists and the academic community for not believing that perpetual motion machines are possible. I suppose it's understandable though, unless you actually understand something about thermodynamics and various other aspects of physics (like the tricky little ways in which energy can be lost from a system) it's kind of hard to see why one can't be clever enough to make such a thing.
Actually I think a lot of the confusion arises from people not understanding the definition of a perpetual motion machine. There are essentially two types; PMM1's, which violate the first law of thermodynamics, and PMM2's, which violate the second. Some violate both :p. It's not a perpetual motion machine if it doesn't violate these laws, by definition.
*aside*
1st Law of Thermodynamics - Essentially conservation of energy, cannot be created or destroyed. Machines which claim to produce more energy than they consume are the most clearly impossible types of perpetual motion machines. Many of the "perpetual motion machines" proposed by people actually claim to draw energy from assorted strange sources, which if they in fact do such a thing means they aren't a perpetual motion machine. Usually they don't though.
2nd Law of Thermodynamics - The entropy of the universe is always increasing. Entropy is a measure of the disorder of a system, ie gases are more disordered than solids and so have higher entropy, hotter things are more disordered than colder things, but also note that more spread out things are more disordered than things all packed in close. This doesn't imply things try to become hotter to increase their entropy, quite the opposite actually. It's a little complicated. Anyway it's basically the law that says heat flows from hotter places to colder places (increases the overall disorder of the system, even if it decreases the disorder of the hotter part) and that solutions don't spontaneously unmix themselves. Such things are perfectly allowed by the 1st law.
The important thing to note for the perpetual motion machines is this: You can transform work (highly ordered energy) to heat (highly disordered energy) with 100% efficiency, no problem (in theory). Electric heaters pretty much do this, they are extremely efficient (though note they produce 1kJ of heat for 1kJ of electrical work, while a heat pump style heater can suck in 10kJ of heat from an external cold place as long as you provide 1kJ of work, giving you a total of 11kJ - wastage of heat for your house. It's not as "efficient" in it's energy conversion but in actual fact you get a lot more energy per joule of electricity you burn. Electric heaters are one of the biggest entropy creators we have in society, even though they are almost 100% energy efficient in their conversion of work to heat.
Anyway, the point is you can't go the other way with 100% efficient, ie you can't turn heat energy into work energy without wasting some of it. The feynman perpetual motion machine is a machine that claims to do this, if it's perfectly insulated it seems that the heat input will speed up the gas molecules, which won't lose energy unless they manage to turn the shaft and create work, with 100% conversion. This therefore violates the second law and is a PMM2.

It's worth noting that pretty much all the laws of thermodynamics can be violated on the quantum scale, since they are classical laws after all. However as you increase the length and time scales then everything tends back to the laws of thermodynamics, so don't think your PMM's are off the hook. Even on the quantum scale you can't violate thermodynamics for very long. The second law is easier to violate than the first since it basically boils down to probabilities that a system will be in a certain configuration. There's always the probability that something stupid like all the water jumping out of your glass will happen, but it's very tiny and the probability of it happening continuously is even more vanishingly tiny. So respect the laws of thermodynamics.

Even the planets orbiting the sun aren't a perpetual motion machine. It's a pretty freakin efficient machine, but still not 100%. There are energy loses due to tidal forces, friction with interstellar dust and gas particles and possibly even gravitational waves.

People should really go and learn about these things before they go and get all upset about the academic community giving them crap for "inventing" a perpetual motion machine. You'd have to have pretty convincing evidence if you want to overthrow thermodynamics. Apparantly the US patent office no longer even accepts patent applications for any kind of perpetual motion machine :p.

One other thing: