First Principles of LO LO11984

Thu, 16 Jan 1997 11:50:48 GMT+2

Replying to LO11925 --

Rol said
"But in reality, we not only have solar system 'first principles'
which operate very well, but we can predict with great accuracy the
movements of the planets in the solar system."

On reading this I reflected on attempts by man to predict the
movements of the planets.
Ptolomy did so using a model consisting of 80 circles.
Copernicus did the same thing using 34 circles. Both models
predicted movements well but both are fundamentally wrong. Ptolomy
saw the sun as the centre of the universe and everything moving in
circular orbits around it. Copernicus used a model with the earth as
the centre - he spent some time in irons for this heresy! Years
later Kepler entered the debate with a new systems model - he pointed
out that planets move in elliptical (not circular) orbits.
The interesting feature for me in these examples is the systems
thinking aspect.
Please allow me to go on a little, and then make a statement.

An erroneous systems view which intriques me is that of Aristotle.
He said that force produces motion. And for thousands of years
nobody took this argument further. Enter Galileo (and Newton), with
a more correct systems view: Force produces ACCELERATION which changes
motion. And a whole new world opened up. For years now every
University on earth has taught Newton's laws of motion to
undergraduates in engineering and physics etc.
Now, using Newton's model assume that you are walking up the isle of a
Boeing with velocity v1 and the Boeing is travelling with velocity v2
then to an observer on earth you will be moving with velocity V =
v1+v2. Wrong! Because if v1 and v2 are the speed of light how can
you travel at twice that speed? Einstein showed us that the correct
expression is:
V = (v1+v2)/(1+(v1v2/c**2)) where c is the speed of light.
Furthermore, whereas Newton viewed time as a constant, Einstein saw
it as a variable and that as a body approaches c time approaches zero.

Now for my statement. In systems engineering we need to distinguish
between Validity and Truth (with acknowledgement to Thomas Saaty).
Ptolomy's model was cumbersome and neither valid or true. But
Newton's models although they can be refuted (they are not
TRUE models of the real world), are most certainly valid for all
practical purposes.
In the real world we constantly make use of systems models, but it is
essential to realise that they are usually not TRUE models of reality.
The point is: Are they valid?
One of the first principles of systems engineering for LO development
is (IMHO) to establish the degrees to which our models are VALID.
This knowledge will enable us to decide how far we can stretch them.
And if we can establish neither their Truth or Validity we should
scrap them - or use extreme caution.


KeithKeith Sandrock Systems/Johannesburg Technology (JOHANTEC)
FAX 27-11-339-7997



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