Re: Some Contradictory Claims in SR:

From: Gregory L. Hansen (glhansen_at_steel.ucs.indiana.edu)
Date: 02/10/05 

Date: Thu, 10 Feb 2005 21:58:12 +0000 (UTC)

In article <5bQOd.24708$i42.6590@fe1.columbus.rr.com>,
kenseto <kenseto@erinet.com> wrote:
>
>"Gregory L. Hansen" <glhansen@steel.ucs.indiana.edu> wrote in message
>news:cugi16$pv9$1@rainier.uits.indiana.edu...
>> In article <VoOOd.1326$Cs5.174@fe2.columbus.rr.com>,
>> kenseto <kenseto@erinet.com> wrote:
>> >
>> >"Gregory L. Hansen" <glhansen@steel.ucs.indiana.edu> wrote in message
>> >news:cugatn$nan$1@rainier.uits.indiana.edu...
>> >> In article <lRMOd.24678$i42.2948@fe1.columbus.rr.com>,
>> >> kenseto <kenseto@erinet.com> wrote:
>> >> >
>> >> >"Gregory L. Hansen" <glhansen@steel.ucs.indiana.edu> wrote in message
>> >> >news:cug17p$k78$1@rainier.uits.indiana.edu...
>> >> >> In article <QrLOd.24664$i42.1244@fe1.columbus.rr.com>,
>> >> >> kenseto <kenseto@erinet.com> wrote:
>> >> >> >
>> >> >> >"Gregory L. Hansen" <glhansen@steel.ucs.indiana.edu> wrote in
>message
>> >> >> >news:cudl3h$keg$1@rainier.uits.indiana.edu...
>> >> >> >> In article
><1107972609.661893.315380@f14g2000cwb.googlegroups.com>,
>> >> >> >> PD <pdraper@yahoo.com> wrote:
>> >> >> >> >
>> >> >> >> >kenseto wrote:
>> >> >> >>
>> >> >> >> >> > length of a stick flying by at 20 m/s? Be careful here. I'm
>> >asking
>> >> >> >> >you
>> >> >> >> >> > do define length measurement.
>> >> >> >> >>
>> >> >> >> >> Sigh....you don't and can't *measure* the length of a moving
>> >ruler.
>> >> >> >> >You
>> >> >> >> >> *predict* its length using IRT or LT. In the case of IRT it
>> >posits
>> >> >> >> [...]
>> >> >> >>
>> >> >> >> >If all you can do is *predict* the length of a moving ruler, but
>> >you
>> >> >> >> >can't measure it, then you can't test the prediction, and it
>> >becomes
>> >> >an
>> >> >> >> >empty theory.
>> >> >> >> >There MUST be a way to measure a moving ruler, to test the
>theory.
>> >> >What
>> >> >> >> >is that way?
>> >> >> >>
>> >> >> >> He can't even predict it if he can't define length measurement.
>> >> >Whatever
>> >> >> >> he predicts, he can't say that it is length if there is no
>> >definition
>> >> >of
>> >> >> >> length to satisfy.
>> >> >> >
>> >> >> >Hummm...I wonder how Einstein do physics before the light-second wa
>s
>> >> >> >invented to measure length.
>> >> >>
>> >> >> According to his 1905 paper, he used a ruler to measure length.
>> >> >
>> >> >Ah...so why did you say that I can't define length measurement??/
>> >>
>> >> I didn't say that, you did. You said the length of a moving ruler can
>> >> only be predicted, not measured. If you can't define a procedure to
>> >> measure the length, what in the world do you think is being predicted?
>> >
>> >So give me some reference where the length of a moving rod is measured
>> >physically.
>>
>> That is not a necessary condition to defining the meaning of the length of
>> a moving rod.
>
>PD said that he can measure the length of a moving rod and I said you can't
>do that then you came in and said that if you can't measure the length of a
>moving rod then you don't know what is it that you are predicting. So I
>asked you to give me some reference where the length of a moving rod is
>measured.

I said you can't say you're predicting a length if you don't have a
*definition* of length. I'll quote me to spare you the trouble of
scrolling up the unsnipped text.

"He can't even predict it if he can't define length measurement.
Whatever he predicts, he can't say that it is length if there is no
definition of length to satisfy."

It seemed pretty clear to me that PD wasn't asking for more than a thought
experiment that illustrates your definition of length when he said

"For example, how would you measure with a physical non-rubber ruler
the length of a stick flying by at 20 m/s? Be careful here. I'm asking
you do define length measurement."

>
>>You said you can predict the length, but what is it that
>> you're predicting? Whatever it is, why should it be called a length?
>
>Why shouldn't it be call a length if it is measured by a ruler.???

There's more than one way to measure something with a ruler. For
instance, you can lay the ruler along the object to be measured with
"zero" at one end, then slide the ruler along the object, bring it to
rest, and then read the number that corresponds to the other end.

I would not consider that a satisfactory measurement of length. Can I
assume we agree on that? 

-- 
"Beer is living proof that God loves us and wants us to be happy."
 -- Benjamin Franklin

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