Physicists have argued over the meaning of the three laws of thermodynamics since they were written in the nineteenth and early twentieth centuries. The laws say that energy cannot be created or destroyed; that the amount of disorder, or entropy, in an isolated system can never decrease; and that it is impossible to cool an object to absolute zero. But thermo-dynamics is paradoxical. The second law, which also puts limits on how efficiently heat can be converted into work — as happens in a steam engine — is particularly controversial.Physicists do not agree on what the three laws of thermodynamics mean or where they come from. Are they purely the statistical product of trillions of particles interacting, or are they a fundamental part of all physics at any scale? To answer that question you need to understand how they relate to quantum mechanics, which describes the operation of single particles. Consider:
The law says that the production of disorder is irreversible. But some physicists argue that at the microscopic level, this seems to conflict with the laws of mechanics — be they those of Newton or of quantum physics. Mechanical laws, say these researchers, prescribe that all processes can be reversed.I bring this up because it shows again the limits of our physics. It is not just gravity that can't be reconciled with quantum mechanics, a problem that only matters when your are trying to understand black holes or other extreme situations. We cannot even reconcile ordinary thermodynamics, the kind we use to calculate the efficiency of engines, with quantum mechanics. In recent years there has been a great deal of work in this direction, and there have been reports of experiments that confirm our thermodynamic laws operate at the quantum scale. If we can figure this out, it may have all sort of useful applications:
Researchers have come up with different approaches to solving this conundrum, but none has satisfied everyone. “This has always been a bit of a dirty business,” says Christian Gogolin, a physicist at the Institute of Photonic Sciences in Castelldefels, Spain.
Whatever the outcome of these debates, they may have implications for future technologies. Physicists have made ‘quantum heat engines’ — that can turn heat into work at the quantum level. Applications such as quantum computing are moving from the theoretical to the real world, so understanding thermodynamics on a tiny scale could be crucial. “You need to design algorithms that are not just faster,” says Renner, “but also thermodynamically optimized.”