[MCMP] Re: Winter Term 2014/5 Philosophy of Physics Reading Group

[Erik Curiel]

Dear philosophers-physicists,

As it turns out, I will not be able to make the first meeting of the 
philphys reading group on Tuesday.  (I should have no problem attending 
future meetings.)  But, since I read Wilson's article, I figured I would 
go ahead and give y'all some of my comments and questions, which may 
help foster discussion.  (What I say here may give the impression that I 
was not impressed with the article;  that impression would be correct.)

1. I found the discussion of Newton's Second Law in section 2 
particularly disappointing.  Given that Wilson in several places makes 
reference to Newton's own views on various matters, I find it incredible 
that he did not discuss Newton's original formulation of the Second Law, 
which is *quite* different in important conceptual and mathematical ways 
from the more familiar, Eulerian F=ma.  Most importantly, and to speak 
somewhat anachronistically, Newton's formulation is an integral 
equation, relating integrated acceleration to what we would today call 
impulse.  This is particularly important in the context of several 
questions Wilson does discuss, as it allows for the consistent treatment 
of the collision of perfectly inelastic point particles, which F=ma does 
not.  There also should at least have been mention of the issues that 
depend on the class of mathematical functions one will accept as 
representations of possible forces.  If one allows, e.g., distributional 
forces, then one can get discontinuities even in the time-evolution of 
the position of a particle, not just its velocity and acceleration.  And 
yet, for many purposes, it seems difficult to do without distributional 
forces, at least for pragmatic reasons.

2. section 3, p. 6:  Wilson is just wrong that Newton "had no notion 
that energy conservation holds."  The last paragraph of the Scholium to 
the Laws in *Principia* very clearly states a conservation principle for 
energy, though, obviously, Newton does not describe it as such.

3. section 4, p. 8:  I have no idea why Wilson says that, on the 
point-mass approach, "it becomes difficult to see how Newton's laws 
could be shown *false*; at best, they might prove an *inconvenient* 
series of approximations to utilize."  Putting aside the fact that 
Wilson must have meant "at worst" and not "at best", he seems here to be 
doing nothing more than advertising his well known predilection 
for---prejudice in favor of---continuum readings of classical mechanics. 
  He makes no real arguments in favor of the claim, and there seems to 
be an obvious counter-argument:  if finer and finer approximations turn 
out worse and worse, then the most natural reaction would be to reject 
Newton's laws as false.

4. section 5, p. 9: I find his discussion of the supposed 
incompatibility of the point-mass approach and the existence of 
constraints to be, at best, baffling, and, at worst, deeply confused. 
His claim that the wire must be able to "see" the bead's velocity before 
the bead approaches a given point, in order to know the force needed to 
keep the bead on the wire as it passes that point, is just the deeply 
mistaken teleological reading of Newton's Second Law.  The wire doesn't 
"know" or "see" anything.  If the bead stays on the wire as it passes a 
given point with a given velocity, then we know the force the wire 
exerted on the bead at that point.  That's all there is to say.  And, in 
any event, even if one were to be able to make sense of what the hell 
Wilson is talking about here, *nothing* in the discussion indicates that 
it is in any way peculiar to the behavior of *point-masses*.  If there 
is a real problem here, it arises for extended bodies as well.  This is 
just, once again, Wilson's irrational prejudice against pointilliste 
readings of classical mechanics.  (It's not that I'm a particular fan of 
pointilliste readings of classical mechanics---it's just that nothing 
Wilson says against them seems cogent or relevant.)

5. section 5, p. 11: "once the basic 'particles' of mechanics are 
granted any spatial extension at all, they are likely to lose their 
postulated rigidity"---Wilson seems to assume without argument or remark 
that this is a bad thing for the 'basic-particle' view.  The only reason 
I can see for his thinking so is, again, his prejudice in favor of 
continuum-interpretations of classical mechanics.

6. section 5, p. 12: he says that, infinitesimal readings of F=ma, 
though common in textbooks, are a mistake, and that "the considered 
modern opinion" is that F=ma should apply only to extended parts of a 
continuous body.  I have *no fucking idea* what he is talking about. 
First, I have read many works on classical mechanics, and I have never 
once seen that view expressed, by a physicist, by a mathematician, or by 
a philosopher---with the exception of Mark Wilson.  I know he thinks 
highly of himself, but surely even he doesn't think that his saying so 
by itself automatically transforms a statement into "the considered 
modern opinion".  Second, I don't even know what the view means.  The 
only way I can begin to try to make sense of it is to interpret F and a 
in not obvious and highly unorthodox ways, and even then it seems highly 
likely that it just won't hold true most of the time, no matter what one 
does.

7. section 7, p. 14: The question that opens section 7 is silly. 
Nothing else.  Why would any serious philosopher, historian or physicist 
think it is even a well posed question in the first place, much more one 
with an answer?

E

-- 
Erik Curiel

Postdoctoral Fellow
Munich Center for Mathematical Philosophy
Lehrstuhl für Wissenschaftstheorie
Fakultät für Philosophie, Wissenschaftstheorie und Religionswissenschaft
Ludwig-Maximilians-Universität
Ludwigstraße 31
80539 München, Deutschland

http://strangebeautiful.com