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mathematically.
The second point is based on a very general principle, a form of the Second Law of Thermodynamics,
which is that the entropy of the universe is NEVER decreased by any process. This implies that the
activity of any process, as defined above, can never be negative. This is very satisfactory, since our
intuitive idea of activity is that it should be positive or zero.
Note that it is important to define the activity in terms of the entropy of the universe, since it is possible
for a process to decrease the entropy of one part of the universe, but only at the cost of increasing it at
least as much somewhere else.
The third point is that it is additive. By this I mean that if an organic system is analysed into distinct
subsystems, then the activity of the whole will be the sum of the activity of the parts.
The fourth point is that the concept of entropy can be applied to information as well as to thermodynamic
processes. There is therefore the possibility of using it as a concept which will span the full range of our
subject from the atomic processes involved in the simplest biochemical changes to the complex
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Principles of Hypnotherapy (22) Precise definition of activity in terms of rate of change of entropy of system
information processing characterising our higher thought patterns.
I am not aware at present of work which directly connects the thermodynamic entropy change involved
in, shall we say, a certain neurological process, to the informational entropy change - which is at a
different level. Perhaps it is work which has yet to be done. But at least the possibility is there.
At the thermodynamic level it is possible to define the entropy of a process as being the amount of heat
that it delivers to a thermal reservoir held at an absolute temperature of 1oK. The activity of a process is
therefore measured in watts/oK. Since most biological processes are at temperatures which vary very
little from around 310oK (close to blood temperature) we can compare the activity of different processes
simply by comparing their heat output. Thus for practical purposes we may identify the activity of a part
of the brain (say) with the rate of heat production by the mental processes therein. The activity of a
muscle will similarly be measured by the rate at which it is producing heat. The rate of production of heat
is power, measured in watts. A two megawatt power station is twice as active as a one megawatt station;
a two kilowatt electric fire will be twice as active as a one kilowatt fire; a person climbing stairs twice as
fast as another (with the same weight) will be twice as active; two identical neurons firing will be twice
as active as one neuron firing; and the activity of each of these different systems can be compared to a
good accuracy by comparing their thermal powers, or more precisely by comparing the entropy changes
they are producing. The various brain-scanning techniques give measures of brain activity which
correlate well with the above definition.
Another way of conceptualising the third law of thermodynamics is the following. Every naturally
occurring process results in making energy less available for doing work. Energy, as we know, is
conserved. There is the same amount of energy in the world both before and after petrol has been burned.
But at the earlier time the energy is concentrated and available to power a car, while afterwards the
energy is spread through the atmosphere and is no longer available.
The activity of a process is a measure of the rate at which energy is being made unavailable. In today's
ecologically conscious age it will be seen that activity is not therefore an unequivocally good thing. An
efficient process is one which achieves a given change with the minimum change of entropy: the
minimum loss of available energy.
The dynamics of an ecological system may be charted by measuring the flow of energy through it (e.g.
Green et al. (1984)Bib). It should be clear that the precise definition of activity used here could be used
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