noise begets silence

[Philip Sherburne <philip@xxxxxxxxxxxxx>]

> I came across this article in yesterday's New York Times
> (http://www.nytimes.com/2001/02/06/science/06NOIS.html?pagewanted=2) - the
> headline immediately grabbed my eye, naturally.  On reading the piece,
> it's not quite as literally linked to microsound as it first seems, but
> there are certainly some interesting metaphoric or conceptual
> connections...  Anyway, enjoy-
> 
> Phil
> 
> 	In the Mysterious Microscopic World, Noise Begets Silence
> 
> 
> 	By JAMES GLANZ
> 
> Physicists have a history of finding natural laws that fit elegantly into
> the language of mathematics but that become seeming paradoxes when
> expressed with ordinary words. Now, along with particles that behave as
> waves and vice versa, they have a new paradox to entertain them: noise
> that makes certain systems in nature quieter.
> 
> In a paper titled "Noise Suppression by Noise," which was published
> yesterday in the journal Physical Review Letters, two physicists have
> found that the noise, or random fluctuations, generated by particular
> types of microscopic systems can actually be quieted when more noise is
> added from the outside.
> 
> The practical consequence of the work may be to show that some systems in
> nature, like biological cells, may already be using the effect to operate
> more efficiently and smoothly, since noise of various types is abundant in
> natural environments. The work could also someday help scientists
> understand certain types of advanced circuitry in which noise, or static,
> is unavoidable.
> 
> The finding's immediate effect, however, will be to pull back the veil a
> little further on the strange workings of the microscopic world.
> 
> In everyday experience, said Dr. Jose M. G. Vilar of the molecular biology
> department at Princeton, who is the paper's lead author, "We put more
> noise in and we get more noise out."
> 
> But the systems he studied with his colleague in the research, Prof.
> Miguel Rubí, of the department of fundamental physics at the University of
> Barcelona in Spain, have what mathematicians call "nonlinear" behavior,
> scrambling that direct relation. Some of those systems, Dr. Vilar and Dr.
> Rubí found, reverse ordinary intuition.
> 
> "You put noise in the system and it displays less noise," Dr. Vilar said.
> 
> Prof. Charles Doering, of the mathematics department of the University of
> Michigan, said the findings added to a growing recognition that noise in
> many biological and physical systems could actually make them more
> sensitive and efficient, rather than being only a source of confusion.
> 
> "The bottom line is that noise can be extremely beneficial," Professor
> Doering said. "It can act as a lubricant to make things work better and
> smoother."
> 
> The first collision of mathematics and ordinary language comes in defining
> the "noise" considered in the research. The noise in question mostly
> involves random fluctuations in the flow of particles and electrical
> current in microscopic systems like cell membranes and advanced circuitry.
> 
> Physicists call those fluctuations noise because, like static in a stereo
> system, they add to some steady signal and confuse it. In a cell, the
> noise may consist of fluctuations in the flow of particles through so-
> called ion channels in a membrane, while in advanced circuit elements
> called quantum dots it consists of jumps and dips in an otherwise steady
> and predictable current.
> 
> Each of those systems produces its own intrinsic or internal noise. Ion
> channels, for example, open and close to regulate the flow of electrically
> charged atoms called ions, and because the process is not perfectly
> regular, the steady flow is complicated by noise. The work by Dr. Vilar
> and Dr. Rubí shows that, strangely enough, any additional noise - caused,
> say, by the jostling of other molecules or by externally applied
> electrical fields - can actually quiet the flow of ions, making it
> smoother and more regular.
> 
> Although the findings are largely theoretical, they could have practical
> consequences, since systems like the ion channel often operate in
> configurations that produce large amounts of internal noise - exactly the
> situation in which the new calculations say external noise could quiet the
> flow. Similar conclusions may hold for quantum circuits and other related
> systems. 
> 
> 	Dr. Vilar said that the effect could allow those systems to operate
> more smoothly in configurations with just the right amount of average or
> steady flow, but also with lots of internal noise. Adding external noise
> would not change the average value but would quiet the fluctuations.
> 
> 	"You have a system which in some places displays a lot of noise, but
> you like those places," Dr. Vilar said. "And other places which don't
> display much noise, but you don't like those places."
> 
> 	By adding external noise, he said, "basically, you get the best of
> both parts."
> 
> 	"You get the noise of one and the average of the other," he added.
> 
> 	As always with the verbal "paradoxes" of physics, the hard part is
> explaining in common language how and why the phenomenon works.
> 
> 	It helps to visualize how an ion channel or a quantum dot operates
> normally. Because nature is grainy on the microscopic level, with
> everything made up of particles and lumps of charge, both systems operate
> like a door that lets people through. Since the door cannot open partly
> and let "half a person" through, the flow rate depends only on how
> frequently the door is opened to let whole people through.
> 
> 	That means flow in the ion channel, for instance, can be regulated
> from zero to intermediate values to some maximum depending on whether the
> "door" is always closed, open as often as closed or always open. Not
> surprisingly, the intrinsic noise, or random fluctuations in the flow,
> occur for those intermediate values, where slight variations in the door's
> behavior have the most effect. Constantly closed or open doors permit no
> variation.
> 
> 	But it is exactly in those intermediate regimes that the channel is
> likely to operate most often as it adjusts to the needs of the cell (as,
> for example, when neuron cells take on or expel charge as part of their
> electrical firing). An external jitter of some kind can in a sense knock
> the system away from its noisiest point of operation without affecting the
> average flow, the calculations showed. In a sense, the door becomes pinned
> against a doorjamb briefly enough to still the intrinsic noise and not
> affect the passage of the people.
> 
> 
> 
> 
> 
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