Is Length Contraction Physically Real??

On May 20, 9:49*pm, Tom Roberts wrote in
sci.physics.relativity:
kenseto wrote:
Is Length Contraction Physically Real??

This depends CRUCIALLY on what one means by "physically real". Your
basic problem is attempting to use such an AMBIGUOUS phrase.

The SR answers to this question are as follows:

You are not competent to describe SR. You got several important aspects
wrong, and your phrasing is atrocious (excessively ambiguous).

1. Nothing physcially is happening to a moving rod.

Hmmm. If you mean that the rod is unchanged to a co-moving observer,
then OK. But, of course, the rod is PHYSICALLY MOVING -- is that a
"happening" or not? I think most people would say that it is.

2. Length measurement is observer dependent.

Not necessarily, it depends on what you mean. But yes, observers at rest
in different inertial frames that use the standard method of measuring
lengths can obtain different results for the measurement of the length
of a given object.

However there is no
direct measurement of physical length contraction ever been
performed.....in fact it is impossible to do so.

It is not impossible to do so, it's just that so far nobody has
conceived of a technique that has a resolution smaller than the effect
to be measured.

3. The measured length of a moving rod is the geometric projection of
the moving rod unto the observer's frame.

Yes, for the standard method of measuring lengths.

This assertion seems to
imply that length contraction is not physically real. It implies that
it is a perspective effect.

Here comes the crux of your problem: what do you mean by "physically
real"? Perspective in general does not affect the object being observed,
but DOES have real, measurable effects, that can be described as
"physically real". For instance, a long ladder will fit through a narrow
door in some orientations but not others -- this is "physically real" to
someone trying to carry the ladder through the door, but is the very
same perspective effect you are discussing. Rotations of the ladder do
not affect the ladder itself, but they DO affect the relationship
between ladder and door, and this can have physical effects (fits
through or not).

4. Length contraction is physically real in the direction of motion of
the rod.

What do you mean by "physically real"? -- such ambiguous phrasing is
useless.

A thin circular rod will physically contracted to a small
circle at the speed of light.

Such a rod cannot move at the speed of light. Nor can any observer.

5. Length contraction is physically real because a 80 ft long pole can
be physically trapped inside a 40 ft long barn briefly if the pole is
moving fast enough wrt the barn. This conclusion is made from the barn
frame's point of view.

Hmmm. Theoretically I guess so, but nobody has actually performed such a
feat!

Here you focus on one aspect of "physically real" (a different aspect
than you used above). Neither pole nor barn are physically affected by
this, so one can also say that length contraction is NOT physically
real. THAT'S the problem with using ambiguous phrases.

Roberts Roberts when you say that "neither pole nor barn are
physically affected by this", you obviously rely on your criminal
brothers who can reopen the doors of the barn "pretty quickly":

http://www.math.ucr.edu/home/baez/ph...barn_pole.html
"These are the props. You own a barn, 40m long, with automatic doors
at either end, that can be opened and closed simultaneously by a
switch. You also have a pole, 80m long, which of course won't fit in
the barn....So, as the pole passes through the barn, there is an
instant when it is completely within the barn. At that instant, you
close both doors simultaneously, with your switch. Of course, you open
them again pretty quickly, but at least momentarily you had the
contracted pole shut up in your barn."

Assume Roberts Roberts that, in some case, your criminal brothers
forget to reopen the doors "pretty quickly". Would then the effect be
one of perspective, or similar to that of an atomic bomb or somehing
entirely different will happen but always in perfect accodance with
the predictions of Divine Albert's Divine Theory?

Pentcho Valev