Re: SR cannot determine Contraction

On Feb 24, 8:45 pm, PD <TheDraperFam...@xxxxxxxxx> wrote:
On Feb 24, 10:31 pm, Dono <sa...@xxxxxxxxxxx> wrote:



On Feb 24, 8:25 pm, PD <TheDraperFam...@xxxxxxxxx> wrote:

On Feb 24, 10:09 pm, Dono <sa...@xxxxxxxxxxx> wrote:

On Feb 24, 7:36 pm, "Artful" <art...@xxxxxxxxxx> wrote:

Nicely put. Now we've just got to convince dono that an object *does*
'physically' have a shorter spatial length (ie take up less physical space;

I had a hunch that you will not get this. This is what happens when
you are more interested in being always right instead of getting it
right <shrug>

Let's put it this way. Length is a result obtained through a
prescription, one that typically involves recording two spatial
locations simulataneously. Length is a physical property. However,
because simultaneity is frame-dependent, the physical property length
is also frame-dependent. There is, however, no physical process or
interaction occurring to or in the rod to change its length.

PD

Correct.
-This is why one can't close the doors simultaneously in the barn
frame without hitting the pole.

In the frame in which the barn is at rest, you can.


No , you can't. This would be equivalent with a physical contraction
of the rod and this is not what is going on.


-This is why the pole in the barn, being a thought experiment, is a
very poor illustration for length contraction.

I don't follow this.

There is a large class of thought experiments (the pole in the barn
being one of them) that rely on the misguided idea that length
contraction allows larger objects (like the pole) to fit inside
smaller enclosures (like the barn) as a byproduct ofrapid relative
motion. This is not the case.


-This is why, to date, we have no experimental test for length
contraction (http://www.edu-observatory.org/physics-faq/Relativity/SR/
experiments.html#Length_Contraction)

I don't follow that, either. What does the frame-dependence of length
do to prohibit measuring that effect, when the frame-dependence of
just about any other frame-dependent quantity has certainly been
measured? (E.g. muon lifetime in g-2, angular distributions of
secondary particles in hadron-hadron collisions, etc.)

Length contraction is a measurement artifact that comes about when we
attempt to measure lengths of moving objects. It is easy to prove that
the effects are of the second order in v/c, something well outside the
current precision of measuring devices.
If, by contrast, length contraction were a physical effect,
compressing objects such that , at relativistic speeds they would fit
into much smaller enclosures (like in the case of the paradox in
discussion) we would have been able to measure it through tension/
stress effects. This is not the case, so we dont' have any tests of
length contraction to date, and probably none for the forseable
future:

http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html#Length_Contraction

.

Relevant Pages

  • Re: SR cannot determine Contraction
    ... because simultaneity is frame-dependent, the physical property length ... In the frame in which the barn is at rest, ... very poor illustration for length contraction. ... do to prohibit measuring that effect, ...
    (sci.physics.relativity)
  • Re: TOM ROBERTS - Dono is confused, please help him out (was SR cannot determine Contraction)
    ... that there are some indirect results that support length contraction. ... He says the pole and barn thought ... "Uniform relative motion cannot make a longer object fit inside ...
    (sci.physics.relativity)
  • Re: The Impossibility of Spacelike Length Contraction
    ... :> THE IMPOSSIBILITY OF SPACELIKE LENGTH CONTRACTION ... :> methods of measuring a length in a moving inertial frame by ... :> 1) A light pulse is sent from one end of the moving length to ... you are - at a fundamental level - comparing waves with waves. ...
    (sci.physics.relativity)
  • Re: Bomb paradox
    ... > was inside the barn at T in Observer SR. ... But it happens in *all* stationary Observer's realms. ... Length contraction is supported by *measurement*. ... David A. Smith ...
    (sci.physics.relativity)
  • Re: What is LET?
    ... and how it refuted the FitzGerald-Lorentz contraction. ... Yes, it happens in the lab frame, but it can't be measured there. ... way as the object you are measuring, ...
    (sci.physics.relativity)