Re: How can I tell if F is a string or if it is a number?

In article <b80891ea-0acf-44ca-a236-c72f80a2fb01@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Pioneer1 <1pioneer1@xxxxxxxxx> wrote:
Maybe I'm misunderstanding you but that force assumed by Newton does not
even enter the orbital formulas.

It *does* enter the formulas, in Newton's formulation of the situation.

I don't know how galaxy collisions work, so you may be right. But I am
not reasoning from an example.

Yes, you *are* reasoning from just an example, namely the simple case of a
two-body problem. Kepler's rules are good enough for such a simple case.
But what happens when you have more than two bodies? What is Kepler's rule
in that case? There is no Kepler law for three bodies. How do you propose
to account for three-body motion with appealing to the concept of force?

I see that Newton's
definition of force adds nothing to Kepler's rule because what Newton
adds, the force term, must always be eliminated to recover Kepler's
rule. And there is no other rule that Newton discovered.

Not true. I think it would help your understanding greatly if you made a
serious attempt to analyze the motion of three bodies of roughly equal size.
You will then see that Kepler's laws don't work. They work in the solar
system only because the sun is so much more massive than any other body, so
you can approximate the situation by assuming that the sun is fixed.

Newton's laws, however, work just fine.

The theory of gravitation that you mention is the consistent system of
units that was developed over many centuries by Laplace, Euler, Gauss,
Lagrange, Hamilton and many others. This system is made of many
algorithms developed to use the Keplerian proportion with units within
physics. These algorithms are independent of the doctrine of causes
and forces invented by Newton. I believe that the general principle
that unifies physics is not the Newtonian force but the unit system.
Do you have any comments about this?

Your comments about "Keplerian proportion with units" are simply false.
Again, try to analyze three bodies.

However, suppose I correct that error for you, and rephrase what you are
saying in a way that is not obviously false. There is a distinction in
the philosophy of science between "realism" and "anti-realism." Roughly
speaking, realism is the doctrine that the objects in our physical theories
correspond to real things in the physical world, and anti-realism is the
doctrine that our physical theories are merely computational algorithms
for predicting observations.

One can, of course, be a realist about some things and an anti-realist about
others. Presumably, you are a realist about concepts like "distance." That
is, the earth really is some distance from the sun in the real world, and
"distance" is not merely a convenient computational concept that we use in
our physical theories, that has no correlate in the real world. On the other
hand, you seem to be arguing for an anti-realist attitude towards Newtonian
forces. That is, according to you, Newtonian forces do not exist in the real
world; they are merely a convenient computational device that we use to
predict our observations.

It can be fruitful, as a thought experiment, to adopt realist and
anti-realist attitudes towards various concepts in physics, to see where that
leads you. Adopting an anti-realist attitude towards Newtonian force might
lead you to think of the principle of equivalence between gravitation and
acceleration and therefore to general relativity. Adopting a realist
attitude towards the wavefunction in quantum mechanics might lead you to the
Everett or "many-worlds" interpretation of quantum mechanics. Adopting an
anti-realist attitude towards motion might lead you to Zeno's paradoxes. So,
I am not discouraging you from exploring these ideas.

However, regardless of your stance on realism versus anti-realism, you still
have to get your calculations right. And to repeat, Kepler won't be good
enough when you go beyond two bodies.
--
Tim Chow tchow-at-alum-dot-mit-dot-edu
The range of our projectiles---even ... the artillery---however great, will
never exceed four of those miles of which as many thousand separate us from
the center of the earth. ---Galileo, Dialogues Concerning Two New Sciences
.

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