In Which Maxwell's Demon Plays a Starring Role and Takes on Entropy: Physicists Convert Information Into Energy

[Mark Kohut]

Pynchon has always known it is about information, yes?


Thursday, September 30, 2010
Physicists Convert Information  Into Energy
The first demonstration of an information-heat engine could  revolutionise the 
way nanomachines get their power.
Here's a fascinating piece of work. Build a tiny staircase and place a small  
polystyrene bead on the bottom step (a staircase is fairly straightforward to  
construct using electric fields). 

It's easy to see the bead being jostled around by the random motion of  
molecules in the surrounding air, the well-known phenomenon of Brownian motion. 

Most of the time, the Brownian motion tends to knock the bead down the stairs  
but sometimes the jostling is powerful enough to push the bead up a step. 

Keep a close eye on the bead using a video camera and every time you see it  go 
up a step, change the electric field so that it cannot drop back down again.  
This is like placing a barrier behind the bead.
As you repeat this process, the bead will move up the staircase, driven by  
Brownian motion. 

This is exactly the experiment that Shoichi Toyabe at Chuo University in  Tokyo 
and a few buddies have successfully carried out. The implication is that  the 
bead is somehow able to extract energy from the environment, which at first  
sight, looks like a blatant violation of the 2nd law of thermodynamics .
Of course, there's more to this than first appears. Toyabe and co's work is  an 
experimental version of the famous Maxwell's demon. Imagine a box filled with  
air but divided in half by a barrier. Maxwell's demon is an imaginary being  
capable of opening the barrier to allow fast moving molecules through while  
closing it for slower ones. 

Eventually, the fast moving molecules end up on one side of the barrier which  
becomes hotter than the other side, even though no energy has been added to the  
system. 

The question is whether or not Maxwell's demon violates the 2nd law of  
thermodynamics which is that heat cannot flow from a cool to a hot system by  
itself.
The most recent thinking is that Maxwell's demon does not violate the 2nd law  
of thermodynamics because it has to measure the velocity of all the molecules  
before deciding which to let through and this requires energy. When this is  
taken into account, there is no violation.
But here's the curious thing. There is no conventional transfer of energy  into 
the system: no heating or accelerating of molecules or some such. Instead,  
information itself seems to be the medium through which energy is transferred. 

That kind of thinking has been a theoretical curiosity, until now. Toyabe and  
friends' have actually done it, the first experimental demonstration of this  
kind of energy transmission. In effect they've converted information into energy  
in this system. 

There's no violation of thermodynamics here. These guys use a video camera to  
determine the position of the bead so when the camera's energy budget is taken  
into account, everything works out as the laws of thermodynamics predict.
It's hard to overstate the significance of what they've done: they've been  able 
to operate a nanomachine--a stair-climbing bead--using nothing more than  
information as the power supply. 

This, they say, is an entirely new type of engine which they call an  
information-heat engine, and it's not hard to imagine its potential.
It means that it's now possible to power nanomachines using information as  the 
medium to transfer energy, even if there is no direct contact with the  
nanomachine.
The task now will be to shrink the sensing system. A video camera is a hefty  
thing to cart around. It would clearly be handy to find some microscopic way of  
sensing the environment and using the information gathered to power a  
nanodevice. 

It's not yet clear how this can be done but you can bet your bottom dollar  that 
Toyabe and pals are working on it. The idea might even generate a little  
interest elsewhere.
Ref: arxiv.org/abs/1009.5287: Information Heat Engine: Converting  Information 
To Energy By Feedback Control 



-- 
Mark Kohut (& Associates)
646-519-1956

Redburn Press
P.O. Box 8452
Pittsburgh, Pa. 15220
412-937-0906
646-519-1956



      
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