Second Law of Thermodynamics Violated

[Dave Monroe]

July 24, 2002 
Second Law of Thermodynamics Violated

It seems that something odd happens to the second law
of thermodynamics when systems get sufficiently small.
The law states that the entropy, or disorder, of the
universe increases over time and it holds steadfast
for large-scale systems. For instance, whereas a hot
beverage will spontaneously dissipate heat to the
surrounding air (an increase in disorder), the air
cannot heat the liquid without added energy. Nearly a
decade ago, scientists predicted that small
assemblages of molecules inside larger systems may not
always abide by the principle. Now Australian
researchers writing in the July 29 issue of Physical
Review Letters report that even larger systems of
thousands of molecules can also undergo fleeting
energy increases that seem to violate the venerable
law.

Genmiao M. Wang of the Australian National University
and colleagues discovered the anomaly when they
dragged a micron-sized bead through a container of
water using optical tweezers. The team found that, on
occasion, the water molecules interacted with the bead
in such a way that energy was transferred from the
liquid to the bead. These additional kicks used the
random thermal motion of the water to do the work of
moving the bead, in effect yielding something for
nothing. For periods of movement lasting less than two
seconds, the bead was almost as likely to gain energy
from the water as it was to add energy to the
reservoir, the investigators say. No useful amounts of
energy could be extracted from the set-up, however,
because the effect disappeared if the bead was moved
for time intervals greater than two seconds. 

The findings suggest that the miniaturization of
machines may have inherent limitations. Noting that
nanomachines are not simply "rescaled versions of
their larger counterparts," the researchers conclude
that "as they become smaller, the probability that
they will run in reverse inescapably becomes greater."
--Sarah Graham 

http://www.scientificamerican.com/article.cfm?articleID=00003AEF-D7A6-1D3D-90FB809EC5880000

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