Published online 23 July 2002 | Nature | doi:10.1038/news020722-2

News

Second law broken

Small-scale energy fluctuations could limit minaturization.

You might win a couple of games, but you can't beat the house.You might win a couple of games, but you can't beat the house.

Researchers have shown for the first time that, on the level of thousands of atoms and molecules, fleeting energy increases violate the second law of thermodynamics1. This is the tenet that some energy will always be lost when converting from one type to another.

The breach may mean there is a limit to miniaturization and to our understanding of the living world. It suggests that at scales of millionths of a millimetre - where machines may one day operate, and where cells already do - the mechanics of large systems cannot simply be scaled down.

In some ways thermodynamics is like gambling. The first law - that energy cannot be created - tells us 'you can't win'. The second says 'you can't even break even'.

In other words, there is nothing unusual about winning a single game of blackjack, but over many games the house always wins. If a player keeps playing, they must eventually lose. And in thermodynamics, you're not allowed to leave the casino - hence the robustness of the second law.

Denis J. Evans and colleagues have discovered, not how to beat the house, but what happens in the realm between a single coin toss and a weekend in Las Vegas. To do so they measured water molecules' influence the motion of tiny latex beads held between lasers.

They found that over periods of time less than two seconds, variations in the random thermal motion of water molecules occasionally gave individual beads a kick. This increased the beads' kinetic energy by a small but significant amount, in apparent violation of the second law.

The gain is short-lived, and so could never amount to a source of free energy or perpetual motion. But it is big enough to confirm what physicists have long suspected.

Law enforcement

The first and second laws of thermodynamics are considered so fundamental that the United States Patent and Trademark Office will not consider patent applications that claim to violate them - unless a working model is provided with the application.

But violation of the second law of thermodynamics by small ensembles of particles within larger systems is not a new idea. Evans's team predicted it formally a decade ago2. And in 1878, the physicist James Clerk Maxwell wrote in a book review for Nature:

The truth of the second law is ... a statistical, not a mathematical, truth, for it depends on the fact that the bodies we deal with consist of millions of molecules... Hence the second law of thermodynamics is continually being violated, and that to a considerable extent, in any sufficiently small group of molecules belonging to a real body.

For larger systems over normal periods of time, however, the second law of thermodynamics is absolutely rock solid.

Ed Gerstner is the Editor of Nature 's Physics and Materials Portals  

  • References

    1. Wang, G. M. , Sevick, E. M. , Mittag, E. , Searles, D.J. & Evans, D.J. Experimental Demonstration of Violations of the Second Law of Thermodynamics for Small Systems and Short Time Scales. Physical Review Letters 89, 050601, (2002).  | Article | ChemPort |
    2. Evans, D. J. , Cohen, E. G. D. , & Morriss, G. P. Probability of Second Law Violations in Shearing Steady States. Physical Review Letters 71, 2401 - 2404 (1993).  | Article | ISI |