Violations of the second law?


Registered Member
This question involves nanotechnology. We are quickly developing the technology to build mechanical devices on the atomic level. It seems to me, that devices this small should be able to tap latent heat energy to do useful work. Doesn't this violate the second law to thermodynamics?
Any device which can take in heat and output useful work as the only product would violate the 2nd law. It follows, then, that no nanotechnological device could do that.

Did you have something in mind?
Think about photovoltaics. After all, the photons being converted to useful work are just a form of heat (well, typically pretty high heat.) No reason I can see why photovoltaic technology is not possible in infrared domain.

Similarly, I can imagine a nanodevice using thermal vibrations of some crystal to drive some sort of a crankshaft or some such.

So I don't see why it should be impossible to extract useful work from heat. Of course, in order not to violate the second law you can never extract 100% useful work from the heat; you must always lose some of that input energy (e.g. by scattering it into lower-grade forms of heat that you can't take advantage of within the same design.)

I'm not a physicist (I'm an engineer), but within my limited expertise I don't see any problem with heat-driven devices.