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Re: The Rauber Marlow Chronicles



On Mon, 29 Apr 1996, Rick Tarara wrote:

...
Having actually tried to read all of this 'debate', I want to question
Dr. Marlow on one point. While I'm on the 'they ain't forces' side of
this discussion, the one thing I don't follow (and let me be presumptuous
enough to suggest many others have not followed) is the relegating of
Gravity to a 'fictitious' force.

See paul Camp's recent posting clarifying this. Gravitation is not
fictitious -- it can tear things apart. It's just not very strong through
most of the solar system, and MUCH of what pre-Einstein physics said
about gravitation (instantaneous action-at-a-distance force between
objects) was fiction. In other words, pre-1915 gravitational theory was
a mixed bag of fiction and fact. Einstein swept away what was fiction by
his thought experiments involving falling elevators: if you can transform
a dynamical effect out of existence by a kinematical change of reference
frame, then it must not really be a dynamical effect. Since a uniform
-mg effect acting at each point could be transformed away by changing
reference frames, it must be only a kinematical effect. This left
standing out in sharp contrast the true dynamical gravitation -- the
differential stress from point to point == tidal stress == difference
in inertial frames from one point to neighboring points (small throughout
most of solar system, big near neutron stars or black holes), i. e., the
hard residue that cannot be gotten rid of by kinematical changes of
reference frame, and that will be forever confused and lost if we allow
invention of fictitious dynamics.


... but I have trouble with the inertial or near
inertial > frame analysis where gravity produces an acceleration but no
force! > > For the sake of argument, lets make it simple and assume the
earth IS an > inertial frame of reference (stop all rotations). As I sit
here I still > feel the chair pushing me up (could put a scale under me
and measure the > force--but I won't tell what it reads ;). However, I'm
not > accelerating. Therefore, as a good Newtonian, I must assume the net
force on me is zero.

This is not the only conclusion a good Newtonian can come to. You have TWO
options -- 1) the conclusion you chose above; or 2) since you obviously
feel a force pressing on you, and yet you are not accelerating, you could
come to the good Newtonian conclusion that the frame you are using to measure
accelerations is NONINERTIAL, and therefore Newton's laws need not apply
relative to that frame. The existence of these two logical options (as
Spock would say) should then impel all good Newtonians and other truth
seekers to start carefully checking all forces in the vicinity besides the
one so obviously being felt, so that they can decide which option is
correct. Use all available means, checking infrared and other spectral
regions for signs of any posible dissipation from hidden dynamical
processes, Etc. If in the end you decide, really in all honesty there's
just the one force acting, then you will be impelled in the direction
Einstein took. If you were in a local inertial frame, you would not need
such a force to keep you from accelerating, and so you must not be using a
local inertial frame.


What is the other force if its not gravity

In the second option, there is no other force. Gravitation is the very
slight amount of greater stress your ankles experience over what your
head experiences because your ankles are in a region of slightly greater
gravitational curvature than your head is -- and it doesn't cause any
headaches or footaches because it's so unnoticeably small on the scale
we are talking about.

If
someone suddenly pulls the chair out from under me, I now accelerate >
towards the floor--again needing a force to do so--gravity? What's wrong
with gravity as a force in these situations (or have I misunderstood the
argument).

Again, wouldn't you say we have more than one Newtonian option to check
here? In the end I will say only one can be correct, when all dynamical
evidence has been checked (i. e., stress, energy, work, mass, momentum),
but before we have done the necessary checking, we have the two options:
1) postulate a force; 2) postulate a noninertial reference frame.
When we take all the evidence into account, the second option is forced
on us.
The chair, while acting on you with its real E.M. forces was doing real
work on you, and it comes out of the energy balance of the solar system.
When you are freefalling, the only measurable effects on you (with very,
very refined equipment) would be the tidal effects of the inertial grip
of spacetime on you.

I forgot to add in a previous post that all these ideas are also presented
to a class of undergrad general studies majors twice a year in a general
astronomy class, and there doesn't seem to be any particular difficulty.
Just keep the kinematical notions (kinesis == motion [Gk]): position,
velocity, acceleration, in an airtight compartment separate from the
dynamical notions (dyne == force [Gk]): force, work, energy, mass, until
you are ready to allow them to mix in an inertial reference frame. If
you mix them up in noninertial reference frames you are inevitably going
to come out with incorrect dynamical calculations from your kinematical
data.


A. R. Marlow E-MAIL: marlow@beta.loyno.edu
Department of Physics PHONE: (504) 865 3647 (Office)
Loyola University 865 2245 (Home)
New Orleans, LA 70118 FAX: (504) 865 2453