Re: On the "contraction" of a rod in SR

In sci.physics.relativity, PD
<TheDraperFamily@xxxxxxxxx>
wrote
on 12 Dec 2005 07:49:34 -0800
<1134402574.016382.151370@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>:
>
> The Ghost In The Machine wrote:
>> OK, color me slightly annoyed at an irrelevancy, but it's clear
>> that most of the lay press, which doesn't have a clue anyway,
>> is of the opinion that things contract in SR, relative to
>> a moving observer.
>>
>> This is far from the case. All one can say here is that they
>> are *observed* to contract, and even then, one has to be very
>> careful what one is observing, and how the observations are done.
>>
>
> [nice article snipped]
>
> I think there is a simpler way to say this.
> The change in length of an object *does* happen in moving from one
> observing frame to another. However, length is not an intrinsic
> property of an object, and so the change does not imply that something
> *physically happens* to the rod to change one of its properties. Length
> is a result of a procedure that is inherently observer-dependent.
>
> PD
>

It's certainly measurement-method-dependent. :-) I'd otherwise
have to agree, inasmuch that one has to move around in one's
observation-space in order to measure something (with a standard
ruler), fire off something to do a measurement (light beams are
traditional but electrons also work, or simply observe using
the aforementioned Instamatic(tm) and external reference points.

And the last is very hard to do in the dark. :-)

--
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