On 14.03.2012 19:58 meekerdb said the following:
On 3/14/2012 11:51 AM, Evgenii Rudnyi wrote:
...
Then the thermodynamic entropy is subjective. Try to convince in this
engineers who develop engines, or chemists who compute equilibria, and
see what happens.
It is relative not just to the information but the use of that
information. Even if you told an engineer designing a steam turbine the
position and momentum of each molecule of steam he would ignore it
because he has no practical way of using it to take advantage of the
lower entropy that is in principle available. He has no way to flex and
deform the turbine blades billions of times per second in order to get
more power from the steam. The experiment I linked to is extremely
simple so that it is possible to use the information.
Brent
I have looked the paper that you have linked
On 13.03.2012 20:09 meekerdb said the following:
> On 3/13/2012 10:28 AM, Evgenii Rudnyi wrote:
...
>> Could you please give one example from physics (yet please not a
>> thought experiment) where information allows us to reduce entropy?
>
> http://www.nature.com/news/2010/101114/full/news.2010.606.html
>
Experimental demonstration of information-to-energy conversion and
validation of the generalized Jarzynski equality
Shoichi Toyabe, Takahiro Sagawa, Masahito Ueda, Eiro Muneyuki & Masaki Sano
Nature Physics, Volume: 6, Pages: 988–992 (2010)
I should say that I am not impressed. One can make a feedback mechanism
indeed (by the way, it is quite common in engineering), but then in my
view we should consider the whole system at once. What is the
information then and what is its relationship with the entropy of the
whole system?
By the way the information about the position of the bead have nothing
to do with its entropy. This is exactly what happens in any feedback
systems. One can introduce information, especially with digital control,
but it has nothing to do with the thermodynamic entropy.
Then I like
"In microscopic systems, thermodynamic quantities such as work, heat and
internal energy do not remain constant".
The authors seem to forget that work and heat are not state functions.
How work and heat could remain constant even in a macroscopic systems?
I also find the assumption at the beginning of the paper
"Note that, in the ideal case, energy to place the block can be
negligible; this implies that the particle can obtain free energy
without any direct energy injection."
funny. After block is there, the particle will jump in the direction of
the block and it will interact with the block. This interaction will
force the particle to jump in the other direction and I would say the
energy is there. The authors should have defined better what they mean
by direct energy injection.
In essence, in my view the title "information-to-energy conversion" is
some word game. It could work when instead of considering the whole
system in question, one concentrates on a small subsystem. Say if I
consider a thermostat then I could also say that information about the
current temperature is transformed to the heater and thus to energy. I
am not sure if this makes sense though.
Evgenii
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