Groups > sci.physics.relativity > #371503

Re: On length contraction

From	wugi <brol@brol.be>
Newsgroups	sci.physics.relativity
Subject	Re: On length contraction
Date	2015-12-06 21:58 +0100
Organization	Aioe.org NNTP Server
Message-ID	<n427jf$922$1@speranza.aioe.org> (permalink)
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Tom Roberts schreef op 6/12/2015 om 19:35:
> On 12/6/15 12/6/15   11:18 AM, wugi wrote:
>> [...]
>> And their differences turn out to be nicely mutual, so yes
>> A=B/gamma and B'=A'/gamma
>> are not contradictary but obvious.
>> http://home.pi.be/~pin12499/MySRT/LorentzObjects.PNG
>
> Yes, this is correct.
>
>
>> Now, if for its measurement a moving object is not affected,
>> "identical" objects
>> moving wrt each other *are* affected in that they could not "instantly
>> become
>> each other".
>
> No. Though you got it right earlier, here you are in error. Simply
> moving an object does not "affect" it (the object itself), though it can
> affect its relationships to other objects (such as clocks and rulers).

What I meant is that moving objects are affected, not when in inertial 
movement but when switching between such.

> If I take two ladders and rotate one, could they "instantly become each
> other"? -- well I don't know what meaning you attach to that rather
> curious phrase (how could ANY pair of objects "instantly become each
> other"????? -- we cannot perform such magic in the world we inhabit). So
> I'll assume you mean that they are not congruent to each other (e.g. as
> they pass each other moving along an East-West line, at some instant
> their Eastern ends are adjacent but their Western ends are not, as seen
> in either object's rest frame).

That's one of the ways I meant, sure...

> The underlying point in SR is that relatively-moving objects are NOT
> parallel to each other. But the rotation is in a space-time plane, which
> most people are not familiar with. But like the ladders, rotations do
> NOT affect the object itself, just its relationship to other objects
> (e.g. its relationship to rulers in some other frame that are used to
> measure its length as seen by that frame).

Well, I see it less as abstract mathematical rotation and more as "real 
gedanken-"physical movement, ...

>> During the acceleration process that makes one object approach the
>> other's frame, a physical change has to happen, which pertains to the
>> physical
>> reality of length contraction (and time dilation).
>
> This is also wrong. In SR, no "physical change" occurs due to
> acceleration, such that it persists after the acceleration stops. BTW
> this also appears to be true to high accuracy in the world we inhabit
> (unless the acceleration is so large that it breaks the object, making
> it no longer the same object).

... and IMO some 'rearrangement' is really going on during relativistic 
acceleration.
When, as you suggested hereabove, their Eastern ends are adjacent then,
1) the Western end, contracted, of the moving object would have to be 
'forced' to its non-contracted non-moving counterpart, (simultaneity at 
rest system) or
2) the Western end, contracted, of the non-moving object would have to 
be forced to its non-contracted, moving counterpart (simultaneity of 
moving system).
That would be forcing things. A "normal" acceleration would try to pass 
along a continous set of instantaneous inertial systems (Born rigid 
acceleration), but other accelerations generating internal forces are 
easily imaginable.

> In SR this OUGHT to be obvious, because the Principle of Relativity
> directly implies that the laws of physics are the same in any inertial
> frame. So for a given object, the intra- and inter-atomic forces,
> relationships, and distances are the same regardless of which inertial
> frame the object happens to be at rest in. That is, when measured in its
> rest frame, the length of an object and the tick rate of a clock are
> ALWAYS equal to their usual values.
>
> So simply accelerating on object to be at rest in some other inertial
> frame does NOT "change" the object itself.

Acceleration description is mostly limited to local, point-like cases. 
But I'm considering acceleration (gradients) "throughout large 
relativistic rigid objects", which of course is multiple gedanken, but 
anyway.

>> Some classical paradoxes use (or abuse:) this feature.
>
> I don't know what you mean here, since your "feature" is wrong.

I think not;-)
I was thinking TP (frequent argument: time dilation, so A keeps younger 
than B, and B keeps younger than A: paradox!);
and recently the rivet paradox was around here (in one system the bug is 
hit first, in the other the wall, so: impossible!??)
http://hyperphysics.phy-astr.gsu.edu/Hbase/Relativ/bugrivet.html
Some approaches for an answer:
http://math.ucr.edu/~jdp/Relativity/Bug_Rivet.html
http://brianclegg.blogspot.fr/2011_11_01_archive.html
https://www.physicsforums.com/threads/what-is-the-resolution-of-the-the-bug-rivet-paradox-paradox-in-special-relativity.57063/
But I decided to draw my own solution. See
http://home.scarlet.be/~pin12499/draaft/RivetParadox1.jpg
Standpoint of opening. The rivet head is stopped in O, then its other 
end in A. The light signals propagating both events meet
in B.
Region OB generates stretch, and BA pressure. From there the ratio OB 
vs. BA is restored, and stresses vanish: "inertial state reached".

http://home.scarlet.be/~pin12499/draaft/RivetParadox2.jpg
Standpoint of rivet. The rivet end is stopped first, in A; then its head 
in O. Both propagation signals meet, again, in B. Same conclusions further.

So, no paradox. Much ado yet, only because the general formulations 
exaggerate the differences and suggest causal links that are not there.

-- 
guido

Thread

On length contraction kenseto <setoken@att.net> - 2015-12-05 07:55 -0800
  Re: On length contraction Maciej Woźniak <mlwozniak@wp.pl> - 2015-12-05 18:40 +0100
  Re: On length contraction kenseto <setoken@att.net> - 2015-12-05 15:49 -0800
  Re: On length contraction Tom Roberts <tjroberts137@sbcglobal.net> - 2015-12-05 22:39 -0600
    Re: On length contraction Maciej Woźniak <mlwozniak@wp.pl> - 2015-12-06 10:28 +0100
    Re: On length contraction alsor@interia.pl - 2015-12-06 05:40 -0800
      Re: On length contraction Tom Roberts <tjroberts137@sbcglobal.net> - 2015-12-06 09:03 -0600
        Re: On length contraction alsor@interia.pl - 2015-12-09 02:37 -0800
      Re: On length contraction fuller.david@hotmail.com - 2015-12-06 08:14 -0800
        Re: On length contraction fuller.david@hotmail.com - 2015-12-06 08:27 -0800
          Re: On length contraction fuller.david@hotmail.com - 2015-12-06 10:37 -0800
    Re: On length contraction kenseto <setoken@att.net> - 2015-12-06 06:21 -0800
      Re: On length contraction rotchm <rotchm@gmail.com> - 2015-12-06 08:19 -0800
        Stephane Baune tries to correct Ken Shito and, in the process, embarrasses himself "Dono," <sa_ge@comcast.net> - 2015-12-07 08:35 -0800
  Re: On length contraction Thomas Heger <ttt_heg@web.de> - 2015-12-06 08:24 +0100
    Re: On length contraction Poutnik <poutnik4nntp@gmail.com> - 2015-12-06 08:41 +0100
    Re: On length contraction kenseto <setoken@att.net> - 2015-12-06 07:06 -0800
    Re: On length contraction Tom Roberts <tjroberts137@sbcglobal.net> - 2015-12-06 09:20 -0600
      Re: On length contraction Thomas Heger <ttt_heg@web.de> - 2015-12-06 21:43 +0100
        Re: On length contraction Tom Roberts <tjroberts137@sbcglobal.net> - 2015-12-07 09:46 -0600
    Re: On length contraction Odd Bodkin <bodkinodd@gmail.com> - 2015-12-06 15:09 -0600
      Re: On length contraction Tom Roberts <tjroberts137@sbcglobal.net> - 2015-12-07 09:49 -0600
  Re: On length contraction rotchm <rotchm@gmail.com> - 2015-12-06 08:10 -0800
    Re: On length contraction Tom Roberts <tjroberts137@sbcglobal.net> - 2015-12-07 10:01 -0600
      Re: On length contraction rotchm <rotchm@gmail.com> - 2015-12-07 08:28 -0800
        Re: On length contraction Odd Bodkin <bodkinodd@gmail.com> - 2015-12-07 10:57 -0600
          Re: On length contraction mlwozniak@wp.pl - 2015-12-07 22:58 -0800
          Re: On length contraction Thomas Heger <ttt_heg@web.de> - 2015-12-08 08:44 +0100
          Re: On length contraction kenseto <setoken@att.net> - 2015-12-08 14:33 -0800
            Re: On length contraction Odd Bodkin <bodkinodd@gmail.com> - 2015-12-08 17:56 -0600
            Re: On length contraction moroney@world.std.spaamtrap.com (Michael Moroney) - 2015-12-10 20:07 +0000
              Re: On length contraction kenseto <setoken@att.net> - 2015-12-10 13:13 -0800
                Re: On length contraction Odd Bodkin <bodkinodd@gmail.com> - 2015-12-10 17:19 -0600
                Re: On length contraction moroney@world.std.spaamtrap.com (Michael Moroney) - 2015-12-11 02:45 +0000
                Re: On length contraction kenseto <setoken@att.net> - 2015-12-10 21:11 -0800
                Re: On length contraction rotchm <rotchm@gmail.com> - 2015-12-11 06:57 -0800
                Re: On length contraction kenseto <setoken@att.net> - 2015-12-11 19:20 -0800
                Re: On length contraction moroney@world.std.spaamtrap.com (Michael Moroney) - 2015-12-11 19:55 +0000
                Re: On length contraction Plexippus Kritikos <plexik@laertesegidio.org> - 2015-12-11 23:25 +0000
                Re: On length contraction kenseto <setoken@att.net> - 2015-12-11 19:25 -0800
                Re: On length contraction pnalsing@gmail.com - 2015-12-11 19:48 -0800
                Re: On length contraction pnalsing@gmail.com - 2015-12-13 14:33 -0800
                Re: On length contraction moroney@world.std.spaamtrap.com (Michael Moroney) - 2015-12-12 17:27 +0000
                Re: On length contraction Odd Bodkin <bodkinodd@gmail.com> - 2015-12-14 10:12 -0600
                Re: On length contraction kenseto <setoken@att.net> - 2015-12-10 21:08 -0800
                Re: On length contraction Odd Bodkin <bodkinodd@gmail.com> - 2015-12-11 08:04 -0600
    Re: On length contraction kenseto <setoken@att.net> - 2015-12-08 14:26 -0800
      Re: On length contraction Plexippus Kritikos <plexik@laertesegidio.org> - 2015-12-08 22:40 +0000
        Re: On length contraction kenseto <setoken@att.net> - 2015-12-09 06:50 -0800
          Re: On length contraction alsor@interia.pl - 2015-12-09 09:06 -0800
      Re: On length contraction rotchm <rotchm@gmail.com> - 2015-12-09 09:47 -0800
        Re: On length contraction Plexippus Kritikos <plexik@laertesegidio.org> - 2015-12-09 18:11 +0000
          Re: On length contraction Sam Wormley <swormley1@gmail.com> - 2015-12-09 12:32 -0600
            Re: On length contraction alsor@interia.pl - 2015-12-09 11:18 -0800
            Re: On length contraction kenseto <setoken@att.net> - 2015-12-10 06:57 -0800
        Re: On length contraction kenseto <setoken@att.net> - 2015-12-10 06:46 -0800
  Re: On length contraction wugi <brol@brol.be> - 2015-12-06 18:18 +0100
    Re: On length contraction Tom Roberts <tjroberts137@sbcglobal.net> - 2015-12-06 12:35 -0600
      Re: On length contraction wugi <brol@brol.be> - 2015-12-06 21:58 +0100
        Re: On length contraction wugi <brol@brol.be> - 2015-12-06 22:31 +0100
        Re: On length contraction Tom Roberts <tjroberts137@sbcglobal.net> - 2015-12-07 10:16 -0600
      Re: On length contraction John Gogo <jfgogo22@yahoo.com> - 2015-12-06 13:08 -0800
        Re: On length contraction John Gogo <jfgogo22@yahoo.com> - 2015-12-06 14:26 -0800
          Re: On length contraction John Gogo <jfgogo22@yahoo.com> - 2015-12-06 14:38 -0800
          Re: On length contraction John Gogo <jfgogo22@yahoo.com> - 2015-12-06 15:39 -0800
  Re: On length contraction Odd Bodkin <bodkinodd@gmail.com> - 2015-12-06 15:07 -0600
    Re: On length contraction benj <none@gmail.com> - 2015-12-14 02:21 -0500
      Re: On length contraction Odd Bodkin <bodkinodd@gmail.com> - 2015-12-14 10:44 -0600
        Re: On length contraction alsor@interia.pl - 2015-12-14 08:59 -0800
        Re: On length contraction kenseto <setoken@att.net> - 2015-12-14 09:05 -0800
          Re: On length contraction alsor@interia.pl - 2015-12-14 09:48 -0800
          Re: On length contraction Odd Bodkin <bodkinodd@gmail.com> - 2015-12-14 12:18 -0600
            Re: On length contraction kenseto <setoken@att.net> - 2015-12-15 05:49 -0800
              Re: On length contraction Odd Bodkin <bodkinodd@gmail.com> - 2015-12-15 08:21 -0600
                Re: On length contraction mlwozniak@wp.pl - 2015-12-15 23:29 -0800
                Re: On length contraction kenseto <setoken@att.net> - 2015-12-16 07:04 -0800
                Re: On length contraction Odd Bodkin <bodkinodd@gmail.com> - 2015-12-16 09:14 -0600

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