[PEN-L:28230] RE: 2nd Law gone?

["Devine, James" <jdevine@xxxxxxx>]

Title: RE: [PEN-L:28229] 2nd Law gone?

 interesting article, but I think that the idea that the 2nd law of thermodynamics could be "gone" is misled. Rather, the research says that the 2nd law is limited, like Newtonian physics, to certain -- highly relevant -- frames. We knew that physics worked differently at the microcosmic level already (though of course we don't know exactly how enough to satisfy the experts). The fact that the 2nd law kicks in again if the time-frame is long enough (2 seconds, the article says) suggests that its violation for shorter time periods is a lot like friction.

JD

-----Original Message-----
From: Ian Murray
To: pen-l
Sent: 7/19/2002 5:03 PM
Subject: [PEN-L:28229] 2nd Law gone?

Second law of thermodynamics "broken"
09:21 19 July 02
NewScientist.com news service

One of the most fundamental rules of physics, the second law of
thermodynamics, has
for the first time been shown not to hold for microscopic systems.

The demonstration, by chemical physicists in Australia, could place a
fundamental
limit on miniaturisation, because it suggests that the micro-scale
devices envisaged
by nanotechnologists will not behave like simple scaled-down versions of
their larger
counterparts - they could sometimes run backwards.

The second law states that a closed system will remain the same or
become more
disordered over time, i.e. its entropy will always increase. It is the
reason a cup
of tea loses heat to its surroundings, rather than being heated by the
air around it.

"In a typical room, for example, the air molecules are most likely to be
distributed
evenly, which is the overall result of their individual random motion",
says
theoretical physicist Andrew Davies of Glasgow University. "But because
of this
randomness there is always a probability that suddenly all the air will
bunch up in
one corner." Thankfully this probability is so small it never happens on
human
timescales.

To the limit

Physicists knew that at atomic scales over very short periods of time,
statistical
mechanics is pushed beyond its limit, and the second law does not apply.
Put another
way, situations that break the second law become much more probable.

But the new experiment probed the uncertain middle ground between
extremely
small-scale systems and macroscopic systems and showed that the second
law can also
be consistently broken at micron scale, over time periods of up to two
seconds.

Researchers led by Denis Evans at the Australian National University in
Canberra
measured changes in the entropy of latex beads, each a few micrometres
across and
suspended in water.

By using a precise laser beam to trap the beads, the team were able to
measure the
movement of the beads very frequently, and hence repeatedly calculate
the entropy of
the system at short time intervals.

Running in reverse

They found that the change in entropy was negative over time intervals
of a few
tenths of a second, revealing nature running in reverse. In this case,
the bead was
gaining energy from the random motion of the water molecule - the
small-scale
equivalent of the cup of tea getting hotter. But over time intervals of
more than two
seconds, on overall positive entropy change was measured and normality
restored.

The team say their experiment provides the first evidence that the
second law of
thermodynamics is violated at appreciable time and length scales.

Their results are also in good agreement with predictions of the
"fluctuation
theorem", a theory developed at ANU 10 years ago to reconcile the second
law with the
behaviour of particles at microscopic scales.

"The results imply that the fluctuation theorem has important
ramifications for
nanotechnology and indeed for how life itself functions", claim the
researchers.

Journal reference: Physical Review Letters (vol 89, 050601)