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To: js1138
"Think real hard about this. Are the initial positions of the planets required to understand and predict their motions? Take your time on this one."

Your patronizing tone aside, i'll answer it anyway, without hesitation.

OF COURSE THEY ARE! You must define the distance of each of the planets relative to each other and in which plane, you must define their velocities and then define their starting positions at t(0) relative to each other before you "start" your model.

Of course you must know initial conditions. (Hint: for some systems when the force is known and is shown to be constant then you can establish initial conditions from later observations, even when you have incomplete observation. For the life force we know nothing yet. ]

good grief.

678 posted on 09/20/2005 8:40:20 PM PDT by Mark Felton (Those who despise instruction despise their own soul...)
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To: Mark Felton
you must define their velocities and then define their starting positions at t(0) relative to each other

But we have that kind of information for living systems. You were asserting that to study life we need to know the absolute initial conditions.

686 posted on 09/20/2005 9:08:23 PM PDT by js1138 (Great is the power of steady misrepresentation.)
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To: Mark Felton

You do realize, right, that from the point of view of the differential equations that form the mathematical basis of most scientific law, the "initial conditions" need only be a set of conditions known for some arbitrary time, which we call t=0, and not necessarily the condition of the system at its origination. That is, we need only, for example, to know accurately the current position of the plantets to know their positions at all past and future times. That is we can designate the current positions of the planets as the conditions at t=0, and then calculate their positions at any other time, including negative times, which would be past positions and positive times, which would be future times. There's no need to know where the planets were when they were first formed.


786 posted on 09/21/2005 10:02:31 AM PDT by stremba
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