Re: TIME, you old gipsy man

From: PD (pdraper_at_yahoo.com)
Date: 02/11/05 

Date: 11 Feb 2005 08:41:22 -0800

Van wrote:
> PD wrote:
> > Van wrote:
> > > PD wrote:
> > > > Van wrote:
> > > > > Alex wrote:
> > > > > > The theory is quite clear that the seconds are not the same
> > > length
> > > > on
> > > > > > the two clocks.
> > > > >
> > > > > Exactly this is what I am trying to point out. If the seconds
> are
> > > of
> > > > > the same length on the two clocks then it is absolutely
absurd
> to
> > > > prove
> > > > > time dilation of SR.
> > > >
> > > > And again you are missing the point. If you have two meter
sticks
> > > > moving relatively with respect to each other, the centimeter
> > markings
> > > > on each ruler are physically identical, yet the length of each
> > stick
> > > > will be shorter when measured by an observer riding on the
other
> > > stick.
> > >
> > > Well, clearly I do not get it pal. If the lenght of each stick
will
> > be
> > > shorter measured by the observer riding on the other stick then
of
> > > course the centimetre markings on each ruler cannot be physically
> > > identical to that observer.
> >
> >
> > Not so, and here's a nutshell reason.
> >
> > Length is not a property of an object, it is the result of a
> procedure.
> > One sensible procedure to measure an object's (call it A) length is
> to
> > mark the location of one end of A against a ruler (R) held by the
> > observer, and the location of the other end of A against the ruler
R,
> > and subtract the values of the marks on R. Because A might be
moving
> at
> > the time, it's essential to stipulate that the marking of the two
> > locations on R be done at the same time.
> >
> > And here is where the rub is. What is "at the same time" for this
> > observer will not be at the same time for any other inertial
> observer.
>
> In that case how is the length contraction confirmed? Because we can
> never ascertain two events at two different internal frame of
reference
> as simultaneous.
>
> >
> > Furthermore, there is no way to define length to avoid this or
> similar
> > ambiguities. Therefore, length is not an intrinsic property of A.
> > Though nothing happens physically to A by measuring it in a
different
> > inertial frame, the length BY DEFINITION changes.
>
> The length "by definition" changes? I am not able to understand this.

That is the whole point. The definition of length requires that the
endpoints be compared to a ruler simultaneously. Take two observers, O1
and O2, measuring a rod A. O1 measures A according to the procedure and
announces a result. O2 objects, saying "You didn't follow the
procedure, O1, you didn't mark the ends simultaneously!" O1 says, "Did
too!" O2 says, "Did not!" O1 says, "Ok, then, you measure A." O2
follows the procedure and announces a result. O1 screams, "Now YOU
didn't follow the procedure!" O2 yells back, "Did too!" and O1 shouts,
"Did not!"

And there is NO WAY to resolve this, because simultaneity depends on
the frame of reference. Moreover, there is no way to define length that
gets around dependence on simultaneity. Therefore, because simultaneity
is inescapably dependent on the observer, so is length.

This may seem unsatisfying or counterintuitive, but it is nonetheless
true.

And just to pound it in further, there is no "right frame" to establish
true simultaneity or true length.

The good news is that, as a result of abandoning length and time as
inherent and nonmixable properties, we get to replace them with a
single, mixed property, the spacetime interval, which is indeed an
inherent property between two events (independent of observer), and it
simplifies the units that we measure time and space in as well as all
quantities that depend on them.

Getting the content of this highly abbreviated *nutshell* of special
relativity under your belt is the key step toward understanding the
rest of it. To do this, however, will take several passes of reading a
more deliberate account and the working through of several examples on
just this one point before it cements in. I highly recommend the first
three chapters of Spacetime Physics, by Taylor and Wheeler, to aid in
this masonry work.

PD

>
> >
> > PD
> >
> >
> >
> > >
> > >
> > > > If you can't understand that either, then you don't understand
> what
> > > it
> > > > means to measure length.
> > >
> > > May be.
> > > Come mothers and fathers
> > > Throughout the land
> > > And don't criticize
> > > What you can't understand
> > > SR and GR
> > > Are beyond your command
> > > Your old road is
> > > Rapidly agin'.
> > > Please get out of the new one
> > > If you can't lend your hand
> > > For the times they are a-changin'.
> > >
> > > >If you do understand and accept length
> > > > contraction, then I would ask why you have a problem with time
> > > > dilation.
> > >
> > > I do not have a problem with time dilation. I just want to know
how
> > it
> > > happens.
> > >
> > > >
> > > > PD
> > > >
> > > > >
> > > > > >Time is gained or lost in similar way to how length on
> > > > > > a 2D plane is lost if you rotate a rod out of the plane.
Only
> > > > > 'similar'
> > > > > > however, because as Weyl put it, time is thought to be a
> > negative
> > > > > > dimension.
> > > > > >
> > > > > >
> > > > > > for a summary of why see:
> > > > > > http://www.users.globalnet.co.uk/~lka/conz2b.htm
> > > > > >
> > > > > > Best Wishes
> > > > > >
> > > > > > Alex Green
> > > > >
> > > > > Thanks,
> > > > >
> > > > > Van.
> > >
> > >
> > > Thanks,
> > > Van.
>
> Thanks,
> Van.

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