Re: operationally inertial frames

[John Denker <jsd@MONMOUTH.COM>]

At 08:11 AM 10/13/99 -0800, John Mallinckrodt wrote:
> Well... It is certainly possible in some cases to show that you are not in
> a Newtonian inertial frame, but it is *not* possible to show that you are
> even approximately *in* one.

I disagree on operational/philosophical grounds.  I say again that the
operational definition of being *in* one is to do an experiment to detect
violations (with some reasonable level of accuracy).  If you get a null
result (within the chosen accuracy) you are in one.

>  It can be an "appropriate approximation" to
> consider the earth's surface a Newtonian inertial frame even if it is
> *nothing at all* like one.

If it is "nothing at all" like one, the violations should be easy to detect.

> Consider this: To establish that a reference frame is a Newtonian inertial
> frame, you need to demonstrate that it is not accelerating with respect to
> other Newtonian inertial frames, e.g., those that are free floating in
> deep space.

Why does one need to demonstrate that?  Suppose we have two frames
accelerating relative to each other, and relative to the fixed stars.  So
what?  The physics is the same in all of them.  We can have unphysical
discussions about effects are due to gravity and what are due to
acceleration, but who cares?  That would be, as the saying goes, "a
distinction without a difference".  Or as another saying goes, "If you
can't tell the difference, it doesn't matter."  So my suggestion is to call
them all Newtonian frames and be done with it.

For introductory courses it suffices to say that the earth's surface is an
*example* of such a frame (to a useful approximation).  One need not
discuss the existence or nonexistence of other examples.


______________________________________________________________
copyright (C) 1999 John S. Denker             jsd@monmouth.com