On 1/22/2012 1:04 AM, Evgenii Rudnyi wrote:
On 21.01.2012 22:03 Evgenii Rudnyi said the following:
On 21.01.2012 21:01 meekerdb said the following:
On 1/21/2012 11:23 AM, Evgenii Rudnyi wrote:
On 21.01.2012 20:00 meekerdb said the following:
On 1/21/2012 4:25 AM, Evgenii Rudnyi wrote:


2) If physicists say that information is the entropy, they
must take it literally and then apply experimental
thermodynamics to measure information. This however seems
not to happen.

It does happen. The number of states, i.e. the information,
available from a black hole is calculated from it's
thermodynamic properties as calculated by Hawking. At a more
conventional level, counting the states available to molecules
in a gas can be used to determine the specific heat of the gas
and vice-verse. The reason the thermodynamic measures and the
information measures are treated separately in engineering
problems is that the information that is important to
engineering is infinitesimal compared to the information stored
in the microscopic states. So the latter is considered only in
terms of a few macroscopic averages, like temperature and


Doesn't this mean that by information engineers means something
different as physicists?

I don't think so. A lot of the work on information theory was done
by communication engineers who were concerned with the effect of
thermal noise on bandwidth. Of course engineers specialize more
narrowly than physics, so within different fields of engineering
there are different terminologies and different measurement
methods for things that are unified in basic physics, e.g. there
are engineers who specialize in magnetism and who seldom need to
reflect that it is part of EM, there are others who specialize in
RF and don't worry about "static" fields.

Do you mean that engineers use experimental thermodynamics to
determine information?
> Evgenii

To be concrete. This is for example a paper from control

J.C. Willems and H.L. Trentelman
H_inf control in a behavioral context: The full information case
IEEE Transactions on Automatic Control
Volume 44, pages 521-536, 1999

The term information is there but the entropy not. Could you please explain why? Or alternatively could you please point out to papers where engineers use the concept of the equivalence between the entropy and information?


In thinking about how to answer this I came across an excellent paper by Roman Frigg and Charlotte Werndl http://www.romanfrigg.org/writings/EntropyGuide.pdf which explicates the relation more comprehensively than I could and which also gives some historical background and extensions: specifically look at section 4.


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