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> Perhaps a more basic, and more pertinent question related with
> entrophy and information in the context of this list is the relation
> of computability, living beings , the arrow of time and entropy,
> What the paper (http://qi.ethz.ch/edu/qisemFS10/papers/ > 81_Bennett_Thermodynamics_of_computation.pdf) that initiated the
> discussion suggest is that in practical terms it is necessary a
> driving force that avoids random reversibility to execute practical
> computations, this driving force implies dissipation of energy and
> thus an increase of entropy. This is so because most if not all
> practical computations are exponentually branched (Fig 10).
But all computations can been done in a non branched way.
There exists reversible universal machine, and indeed a quantum
computer is such a machine.
From Bennett 73, (Logical reversibility of computation, IBM, J. Res.
Dev., 17, 525).
Energy is dissipated only when information is erased (Landauer
principle), and, as the logicians already knew (Hao Wang, for example)
computations can been done without erasing any information.
Bennett convinced me also that we can extract work from (Shannon)
information, and that energy might be a local measure of information
> And here comes the living beings. As the paper says in the
> introduction, living beings perform computations at the molecular
> level, and it must be said, at the neural level.
I am OK with this, but of course we don't know that.
> Therefore given the
> said above, life must proceed from less to more entrophy and this
> defines the arrow of time.
> Besides the paper concentrates itself in what happens inside a
> computation some concepts can be used to dilucidate what happens with
> the interaction of a living being and its surrounding reality. The
> reality behaves like a form of ballistic computer at the microscopic
> level., with elemental particles ruled by the forces of nature instead
> of ellastic macroscopic collisions. At the macroscopic level,
> however, there is a destruction of information and irreversibility.
> However in the direction of entropy dissipation, it is possible to
> perform calculations in order to predict the future at the macroscopic
> level. That´s a critical function of living beings. An extreme example
> of the difference between macro and micro computation is to "predict"
> the distrubution of water in a water collector after rain. It is not
> necessary to know the position and velocity of every water molecule,
> not even the position and velocity of each drop of water. is this
> erase of information that the increase of entropy perform at the
> macroscopic level (that indeed is the reason of the mere concept of
> macro-state in statistical mechanics) the process that permit
> economically feasible computations. Since computation is expensive
> and the process of discovery of the world by living beings trough
> natural selection very slow, (trough the aggregation of complexity
> and sophistication by natural selection is in the order of magnitude
> of the age of the universe : thousands of millions years) Then the
> macroscopic laws of nature must be simple enough, and there must be a
> privileged direction of easy computation for life to exist.
> The fact that evolution for intelligent life and age of the Universe
> are in the same magnitudes means that this universe is constrained to
> the maximum discoverable-by-evolution complexity in the
> computationally privileged direction of the arrow of time.