Russell,

`I know that many physicists identify the entropy with information.`

`Recently I had a nice discussion on biotaconv and people pointed out`

`that presumably Edwin T. Jaynes was the first to make such a connection`

`(Information theory and statistical mechanics, 1957). Google Scholar`

`shows that his paper has been cited more than 5000 times, that is`

`impressive and it shows indeed that this is in a way mainstream.`

## Advertising

I have studied Jaynes papers but I have been stacked with for example

`“With such an interpretation the expression “irreversible process”`

`represents a semantic confusion; it is not the physical process that is`

`irreversible, but rather our ability to follow it. The second law of`

`thermodynamics then becomes merely the statement that although our`

`information as to the state of a system may be lost in a variety of`

`ways, the only way in which it can be gained is by carrying out further`

`measurements.”`

`“It is important to realize that the tendency of entropy to increase is`

`not a consequence of the laws of physics as such, … . An entropy`

`increase may occur unavoidably, due to our incomplete knowledge of the`

`forces acting on a system, or it may be entirely voluntary act on our part.”`

`This is above of my understanding. As I have mentioned, I do not buy it,`

`I still consider the entropy as it has been defined by for example Gibbs.`

`Basically I do not understand what the term information then brings. One`

`can certainly state that information is the same as the entropy (we are`

`free with definitions after all). Yet I miss the meaning of that. Let me`

`put it this way, we have the thermodynamic entropy and then the`

`informational entropy as defined by Shannon. The first used to designe a`

`motor and the second to design a controller. Now let us suppose that`

`these two entropies are the same. What this changes in a design of a`

`motor and a controller? In my view nothing.`

By the way, have you seen the answer to my question: >> Also remember that at constant volume dS = (Cv/T) dT and dU = >> CvdT. If the entropy is information then its derivative must be >> related to information as well. Hence Cv must be related to >> information. This however means that the energy also somehow >> related to information.

`If the entropy is the same as information, than through the derivatives`

`all thermodynamic properties are related to information as well. I am`

`not sure if this makes sense in respect for example to design a`

`self-driving car.`

`I am aware of works that estimated the thermodynamic limit (kT) to`

`process information. I do not see however, how this proves the`

`equivalence of information and entropy.`

Evgenii

`P.S. For a long time, people have identified the entropy with chaos. I`

`have recently read a nice book to this end, Entropy and Art by Arnheim,`

`1971, it is really nice. One quote:`

`"The absurd consequences of neglecting structure but using the concept`

`of order just the same are evident if one examines the present`

`terminology of information theory. Here order is described as the`

`carrier of information, because information is defined as the opposite`

`of entropy, and entropy is a measure of disorder. To transmit`

`information means to induce order. This sounds reasonable enough. Next,`

`since entropy grows with the probability of a state of affairs,`

`information does the opposite: it increases with its improbability. The`

`less likely an event is to happen, the more information does its`

`occurrence represent. This again seems reasonable. Now what sort of`

`sequence of events will be least predictable and therefore carry a`

`maximum of information? Obviously a totally disordered one, since when`

`we are confronted with chaos we can never predict what will happen next.`

`The conclusion is that total disorder provides a maximum of information;`

`and since information is measured by order, a maximum of order is`

`conveyed by a maximum of disorder. Obviously, this is a Babylonian`

`muddle. Somebody or something has confounded our language."`

-- http://blog.rudnyi.ru On 18.01.2012 23:42 Russell Standish said the following:

On Wed, Jan 18, 2012 at 08:13:07PM +0100, Evgenii Rudnyi wrote:On 18.01.2012 18:47 John Clark said the following:On Sun, Jan 15, 2012 at 3:54 PM, Evgenii Rudnyi<use...@rudnyi.ru> wrote: " Some physicists say that information is related to the entropy"That is incorrect, ALL physicists say that information is related to entropy. There are quite a number of definitions of entropy, one I like, although not as rigorous as some it does convey the basic idea: entropy is a measure of the number of ways the microscopic structure of something can be changed without changing the macroscopic properties. Thus, the living human body has very low entropy because there are relatively few changes that could be made in it without a drastic change in macroscopic properties, like being dead; a bucket of water has a much higher entropy because there are lots of ways you could change the microscopic position of all those water molecules and it would still look like a bucket of water; cool the water and form ice and you have less entropy because the molecules line up into a orderly lattice so there are fewer changes you could make. The ultimate in high entropy objects is a Black Hole because whatever is inside one on the outside any Black Hole can be completely described with just 3 numbers, its mass, spin and electrical charge. John K ClarkIf you look around you may still find species of scientists who still are working with classical thermodynamics (search for example for CALPHAD). Well, if you refer to them as physicists or not, it is your choice. Anyway in experimental thermodynamics people determine entropies, for example from CODATA tables http://www.codata.org/resources/databases/key1.html S ° (298.15 K) J K-1 mol-1 Ag cr 42.55 ą 0.20 Al cr 28.30 ą 0.10 Do you mean that 1 mole of Ag has more information than 1 mole of Al at 298.15 K? Also remember that at constant volume dS = (Cv/T) dT and dU = CvdT. If the entropy is information then its derivative must be related to information as well. Hence Cv must be related to information. This however means that the energy also somehow related to information. Finally, the entropy is defined by the Second Law and the best would be to stick to this definition. Only in this case, it is possible to understand what we are talking about. Evgenii -- http://blog.rudnyi.ruEvgenii, while you may be right that some physicists (mostly experimentalists) work in thermodynamics without recourse to the notion of information, and chemists even more so, it is also true that the modern theoretical understanding of entropy (and indeed thermodynamics) is information-based. This trend really became mainstream with Landauer's work demonstrating thermodynamic limits of information processing in the 1960s, which turned earlier speculations by the likes of Schroedinger and Brillouin into something that couldn't be ignored, even by experimentalists. This trend of an information basis to physics has only accelerated in my professional lifetime - I've seen people like Hawking discuss information processing of black holes, and we've see concepts like the Beckenstein bound linking geometry of space to information capacity. David Deutsch is surely backing a winning horse to point out that algorithmic information theory must be a foundational strand of the "fabric of reality". Cheers

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