Re: Androcles and Draper resume Einstein 1905

From: PD (pdraper_at_yahoo.com)
Date: 01/15/05 

Date: 15 Jan 2005 04:40:30 -0800

Androcles wrote:
> "Gregory L. Hansen" <glhansen@steel.ucs.indiana.edu> wrote in message

> news:cs9uc5$fcl$2@rainier.uits.indiana.edu...
> > In article <NA_Fd.135846$48.119998@fe1.news.blueyonder.co.uk>,
> > Androcles <dummy@dummy.net> wrote:
> >>
> >>"Gregory L. Hansen" <glhansen@steel.ucs.indiana.edu> wrote in
message
> >>news:cs9rcd$dvn$4@rainier.uits.indiana.edu...
> >>> In article <p3WFd.96280$C8.24495@fe3.news.blueyonder.co.uk>,
> >>> Androcles <dummy@dummy.net> wrote:
> >>>>
> >>>>"Gregory L. Hansen" <glhansen@steel.ucs.indiana.edu> wrote in
> >>>>message
> >>>>news:cs99n4$79r$1@rainier.uits.indiana.edu...
> >>>>> In article <B0VFd.95629$C8.85428@fe3.news.blueyonder.co.uk>,
> >>>>> Androcles <dummy@dummy.net> wrote:
> >>>>>>
> >>>>>>"PD" <pdraper@yahoo.com> wrote in message
> >>>>>>news:1105729764.441171.196420@c13g2000cwb.googlegroups.com...
> >
> >
> >>>>>>> This is all covered in the section in Einstein's paper in the
> >>>>>>> section
> >>>>>>> on the relativity of simultaneity.
> >>>>>>
> >>>>>>Does the K-observer conclude the k-rod is shorter than the
K-rod,
> >>>>>>or not? Yes/No.
> >>>>>>There can be no ambiguity to the question.
> >>>>>>"Neither" is not an acceptable answer.
> >>>>>>I didn't ask you
> >>>>>>"Does the k-observer conclude the K-rod is shorter than the
> >>>>>>k-rod?"
> >>>>>>because I'm not interested in the answer at this time.
> >>>>>>Now, please answer my question unanbiguously with a yes or a
no.
> >>>>>
> >>>>> If I may *** in, I think Draper's point was that when K
watches k
> >>>>> measure
> >>>>> the length, he won't agree that it was a measurement of the
> >>>>> length!
> >>>>> And
> >>>>> vice versa. So when k gives K a measured length, K will say
"Your
> >>>>> number
> >>>>> is smaller than mine, but I don't know what the hell it is. I
> >>>>> watched
> >>>>> you
> >>>>> do it, and that's not how to measure a length."
> >>>>>
> >>>>That's fine, but k is carrying out an illegitimate procedure. I
had
> >>>>previously
> >>>>agreed with Paul that the measurement can only be carried out
when
> >>>>the rod to be measured and the measuring rod were relatively at
> >>>>rest.
> >>>>Observer K will not agree with observer k's guesstimate,
> >>>>as you point out, but observer k himself will be uncertain.
> >>>>Androcles.
> >>>
> >>> That seems like an unnecessary restriction. You didn't really
agree
> >>> with
> >>> Paul that the concept of length has no meaning for a moving
object,
> >>> did
> >>> you? Did I misread?
> >>>
> >>> k measures the length of the rod with a ruler that is stationary
> >>> with
> >>> respect to k. It doesn't have to be stationary with respect to
the
> >>> rod,
> >>> but it has to be stationary with respect to k or else it's not a
> >>> measurement of length in k's frame.
> >>
> >>How do you measure the wheelbase of a moving bus or truck
> >>holding a rod wich is stationary with respect to you at the side
> >>of a highway?
> >>
> >>How do you measure one strip of the dotted white line down
> >>the middle of the road holding a rod while travelling in a car
> >>at 70 mph with a calibrated rod in your hand?
> >
> > I see nothing wrong with Einstein's recipie: simultaneously measure

> > the
> > positions of the front and the back.
>
> Stop right there. You've just said "simultaneously".
> Define simultaneous.
> Androcles.
>
>

Precisely! Better yet: define simultaneous in a way that will give
preference to one observer over another.

>
>
>
> How to do that in practice is not as
> > important as the fact that it gives a definite relation of length
to
> > things that had already been defined. But you might, for example,
> > line
> > the road with a sequence of pressure-sensitive plates which
transmit a
> > status (pressed on or not pressed on) at every time interval. Pick

> > two
> > plates that are pressed on at the same time and measure the
distance
> > between them.
> >
> > Place a ruler alongside the road and take a photograph of the bus
as
> > it
> > passes, making due corrections for light propagation time to
eliminate
> > simple optical effects.
> >
> > Run the bus around a racetrack and adjust pylons with contact
switches
> > until both are triggered simultaneously as determined by signals
that
> > travel through cables of equal length connecting each switch to a
> > coincidence detector. Then measure the distance between the
pylons.
> >
> > If you really want to go old school, build a road through a
> > barn. Then when the bus enters the barn, if you can close both
doors
> > simultaneously without hitting the front or back of the bus, you
can
> > at
> > least say that the bus is shorter than the distance between the
doors.
> > And then you might want to open the front door again in a hurry.
> >
> > If we work together on it, we could probably come up with a dozen
more
> > methods. But I'm sure none of that is novel to you.
> >
> > Is it fair to say that your objections to Einstein's conclusions
about
> > length are based on a definition of length that Einstein didn't
use?
> >
> > --
> > "We don't grow up hearing stories around the camp fire anymore
about
> > cultural figures. Instead we get them from books, TV or movies, so
the
> > characters that today provide us a common language are corporate
> > creatures" -- Rebecca Tushnet

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