On 5/16/12 5/16/12 8:46 AM, LaLALa wrote:
> I am shocked that you would say that there is no such thing
> as inertial frame on earth.
This depends on what one means by "inertial frame". As for many terms of the
technical vocabulary, the meaning of this phrase depends on one's theoretical
context:
1) In the context of Newtonian mechanics, an inertial frame is infinite in
extent, and it is implicitly assumed that they exist. Modern observations of the
universe show that assumption to be false.
2) In the context of SR, an inertial frame is also infinite in extent, and there
are indeed no such frames on earth, or anywhere else in the universe.
3) In the context of GR, inertial frames are only local, and their extent
depends on the local curvature of the manifold and upon one's measurement
accuracy (larger curvature or better accuracy implies smaller region of
validity). Extent includes both time and space, and in many interesting cases
the temporal duration is a tighter constraint than spatial size.
Careful authors distinguish among these by never omitting "local" for (3). But
setoken is the antithesis of a careful author, as are many others around here.
Note, please, that Newtonian mechanics includes gravity but SR does not.
One can use a LOCALLY inertial frame here on earth with negligible error, as
long as the measurement errors are larger than the errors due to the assumption
of being an inertial frame. Do that by meeting one of these conditions:
A) one applies Newtonian mechanics in a region no larger than a few
tens of meters, and considers only phenomena on the surface.
B) one applies Newtonian mechanics in a region no larger than a few
radii of Pluto's orbit, and considers only orbital mechanics.
C) one applies SR in a region no larger than a few tens of meters, and
for no longer than a few tens of nanoseconds.
All particle physics experiments, and most tabletop optical experiments, can be
analyzed using SR, because they meet condition (C): at the start of any
measurement, imagine a locally inertial frame at rest relative to the apparatus
but freely falling in earth's gravity; 100 nanoseconds later it will have fallen
a distance that is small compared to the measurement accuracy, so the difference
between this locally inertial frame and the lab frame can be neglected.
Like many/most arguments around here, the actual situation is more nuanced than
either party to the disagreement recognizes.
[I do not address setoken's proposed "experiment", as I have done
so many times before, but he is able to neither read what I write
nor remember anything that was written.]
Tom Roberts