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Breaking even
The idea that the second law of thermodynamics could be violated by small ensembles of particles within larger systems is not new. In 1878, James Clerk Maxwell (writing in a book review for Nature) noted:
For larger systems over normal periods of time, however, the second law of thermodynamics is sound. To explain all this apparent paradox, a useful analogy can be drawn to gambling. Although there is nothing unusual about winning a single game of 'black-jack', it is a matter of statistical fact that over many games, the house always wins. Therefore, 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. The interesting question posed by Wang et al., however, is not how to beat the house, but what happens in the realm between a single coin toss and a weekend in Las Vegas? At length scales where nanomachines may one day operate — and indeed, biological systems such as living cells already do — violation of the second law may have important phenomenological implications. In a previous work, one of the authors developed a framework called the fluctuation theorem to quantitatively describe such violations in finite systems (Evans et al. Phys. Rev. Lett. 71, 2401–2404 (1993)). In the new work, Wang et al. experimentally confirm the predictions of this theorem by observing the influence of water molecules on the motion of microsized latex beads held in an optical trap. They find that over timescales of less than 2 s, fluctuations in the random thermal motion of water molecules can occasionally give individual beads a kick, increasing their kinetic energy by a small but measurable amount, in apparent violation of the second law of thermodynamics. The gain is short-lived, and so could never amount to a source of free energy or perpetual motion. But the results do suggest that as technology approaches ever-smaller dimensions, our understanding of statistical mechanics may have to be more sophisticated than a simple scaling down of macroscopic models. For more materials science and nanotechnology highlights, and free full text access (until 31st October) to all materials and nanotech papers published in Nature, go to Materials Update . Experimental demonstration of violations
of the second law of thermodynamics for small systems and
short time scales |
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The first law of thermodynamics states that it is impossible
to create energy from nothing — or in other words, in terms
of energy, you can't win. Furthermore, the second law states
that, in converting energy from one type to another, some
of that energy will be always be lost in a different form
— or in other words, you can't even break even. These two
laws are considered so fundamental that the United States
Patent and Trademark Office will not even consider patent
applications that claim to violate them (that is, unless a
working model is provided with the application). But writing in
Physical Review Letters this week, Genmiao Wang and colleagues
suggest that violations of the second law of thermodynamics,
albeit at small scales and over short periods of time, can
and do occur.