[ExI] The subjectivity of entropy, the role of the observer...==> Rational metaethics

Bryan Bishop kanzure at gmail.com
Thu Feb 28 16:06:02 UTC 2008

On Thursday 28 February 2008, Jef Allbright wrote:
> <http://www.overcomingbias.com/2008/02/second-law.html>

A good post, it's making me wonder where he's getting his material. 

> The connection in the other direction is less obvious.  Suppose there
> was a glass of water, about which, initially, you knew only that its 
> temperature was 72 degrees.  Then, suddenly, Saint Laplace reveals to 
> you the exact locations and velocities of all the atoms in the water.  
> You now know perfectly the state of the water, so, by the 
> information-theoretic definition of entropy, its entropy is zero.  
> Does that make its thermodynamic entropy zero?  Is the water colder, 
> because we know more about it? Ignoring quantumness for the moment,
> the answer is:  Yes!  Yes it is! 

Saint Laplace, supposedly being a mystical being able to reveal this 
information to you, would have to directly measure all of these pieces 
of information -- otherwise I would have to argue that it is _not_ 
colder. In other words, whether it is St. Laplace or yourself that does 
the measurements: the measurements must be within this universe, else I 
would have to debate the point that it is colder. But this is just 
nit-picking, since the basic point that anything that you know more 
about gets colder. (That's why programmers hate documentation: it's 

> Which is to say:  To form accurate beliefs about something, you really
> do have to observe it.  It's a very physical, very real process: any 
> rational mind does "work" in the thermodynamic sense, not just the 
> sense of mental effort.   

I wonder what the correlation is between thermodynamic 'work' (heat 
cycles?) and mental effort. I know that it's not one-to-one, but still.

- Bryan
Bryan Bishop

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