Groups > sci.physics.relativity > #363368

Re: Bell's spaceship paradox...

From	wugi <brol@brol.be>
Newsgroups	sci.physics.relativity
Subject	Re: Bell's spaceship paradox...
Date	2015-09-07 18:30 +0200
Organization	Aioe.org NNTP Server
Message-ID	<mske4n$2g4$1@speranza.aioe.org> (permalink)
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Tom Roberts schreef op 3/09/2015 om 19:47:
> On 9/3/15 9/3/15   10:32 AM, alsor@interia.pl wrote:
>> W dniu czwartek, 3 września 2015 05:32:04 UTC+2 użytkownik rotchm:
>>> Any third party whant to clear that up? I maintain my stance in that,
>>> the
>>> distance between the ships (their separation), as measured by different
>>> observers (frames), is frame dependent (has different values). I give
>>> the
>>> example again: in the ground frame, the distance remains D0 as the ships
>>> move. In a ship frame (as measured by this ship), the distance of the
>>> other ship will be different from D0.
>>
>> Indeed. This paradox shows just there must exist preffered frame,
>
> Only for this specific physical situation. The ground frame is
> "preferred" in
> that the inter-ship distance is constant in it.
>
> That preference is merely one of human convenience; in particular, there
> are no
> physical phenomena related to it. -- so that is NOT the usual meaning of
> "preferred frame", which SR does not have, and which no experiment has ever
> observed.
>
>
>> Simply: the distance is invariant, and the time is invariant.

Time and again I see this confusion of distance assessment. To define 
distances according to the moving system, one has to consider event 
positions that are simultaneous in its frame, which implies they are NOT 
simultaneous in the "rest"/"preferred"/"starting" frame. That applies 
for proper lengths (moving with the system) as well as third party 
lengths, eg in the rest frame. So one cannot point at a certain moment 
in the rest frame and state "now the distance between the space ships is 
A, BUT the moving system measures distance B between these events".

> That is simply wrong. There are many experiments that verity the "time
> dilation"
> and "length contraction" of SR, and related phenomena. So neither length
> nor
> time can be invariant.

Some side-tracks of BSP.

First, it makes one realise that, generally, strong (relativistically 
speaking) acceleration will not leave the inner structure of an object 
(spaceship, or rope between spaceships...) unstressed, internally that 
is. Imagine a rod, whose left end starts accelerating to the left, and 
the right end responds accordingly but not before the delay imposed by 
final signal speed. Now imagine the same, but with movement to the 
right. I see different stress patterns there...
I seem to have read that unstressed (co-ordinated) forms of acceleration 
exist, or are studied, but I forgot where. (At any moment the object 
should find itself having constant length L0 in its local inertial frame).

Second, BSP has a nice EM counterpart. Imagine, not 2 spaceships but a 
whole row of them, starting moving simultaneously, and next and parallel 
to it another row remaining at rest. Make those spaceships into electric 
charges, negative for the moving ones and positive for the non-moving. 
Then we are dealing with the example of electromagnetism to show 
(relativistically! for speeds of mm/s!!) that magnetic force in one 
frame = electric force in another.
http://galileo.phys.virginia.edu/classes/252/rel_el_mag.html

-- 
guido
http://home.scarlet.be/~pin12499/paratwin.htm

Thread

Bell's spaceship paradox... rotchm <rotchm@gmail.com> - 2015-09-02 20:32 -0700
  Re: Bell's spaceship paradox... "Paul B. Andersen" <relativity@paulba.no> - 2015-09-03 11:27 +0200
  Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-03 08:32 -0700
    Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-03 09:44 -0700
      Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-03 10:23 -0700
        Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-03 12:07 -0700
          Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-03 12:13 -0700
            Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-03 12:39 -0700
              Re: Bell's spaceship paradox... "Lleyton H. Bellucci" <lleyb@stratospheree.org> - 2015-09-03 19:45 +0000
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-03 12:47 -0700
                Re: Bell's spaceship paradox... "Lleyton H. Bellucci" <lleyb@stratospheree.org> - 2015-09-03 19:52 +0000
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-03 13:58 -0700
                Re: Bell's spaceship paradox... "Lleyton H. Bellucci" <lleyb@stratospheree.org> - 2015-09-03 22:03 +0000
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-03 16:52 -0700
              Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-03 12:55 -0700
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-03 13:59 -0700
                Re: Bell's spaceship paradox... Odd Bodkin <bodkinodd@gmail.com> - 2015-09-03 17:05 -0500
                Re: Bell's spaceship paradox... Tom Roberts <tjroberts137@sbcglobal.net> - 2015-09-04 09:55 -0500
                Re: Bell's spaceship paradox... Odd Bodkin <bodkinodd@gmail.com> - 2015-09-04 10:04 -0500
                Re: Bell's spaceship paradox... Tom Roberts <tjroberts137@sbcglobal.net> - 2015-09-04 12:50 -0500
                Re: Bell's spaceship paradox... Odd Bodkin <bodkinodd@gmail.com> - 2015-09-04 13:48 -0500
                Re: Bell's spaceship paradox... Koobee Wublee <koobee.wublee@gmail.com> - 2015-09-04 12:44 -0700
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-04 13:55 -0700
                Re: Bell's spaceship paradox... Maciej Woźniak <mlwozniak@wp.pl> - 2015-09-05 15:09 +0200
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-05 11:51 -0700
                Re: Bell's spaceship paradox... kefischer <emoneyjoe@iglou.com> - 2015-09-04 16:22 -0400
                Re: Bell's spaceship paradox... Robert Winn <rbwinn3@gmail.com> - 2015-09-06 21:59 -0700
                Re: Bell's spaceship paradox... rotchm <rotchm@gmail.com> - 2015-09-07 05:49 -0700
                Re: Bell's spaceship paradox... Robert Winn <rbwinn3@gmail.com> - 2015-09-07 09:04 -0700
                Re: Bell's spaceship paradox... rotchm <rotchm@gmail.com> - 2015-09-07 09:30 -0700
                Re: Bell's spaceship paradox... Robert Winn <rbwinn3@gmail.com> - 2015-09-09 02:41 -0700
                Re: Bell's spaceship paradox... rotchm <rotchm@gmail.com> - 2015-09-09 04:16 -0700
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-04 12:11 -0700
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-04 12:45 -0700
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-04 13:14 -0700
                Re: Bell's spaceship paradox... Tom Roberts <tjroberts137@sbcglobal.net> - 2015-09-05 10:30 -0500
                Re: Bell's spaceship paradox... "Lleyton H. Bellucci" <lleyb@stratospheree.org> - 2015-09-05 15:47 +0000
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-05 09:48 -0700
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-05 09:30 -0700
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-05 11:50 -0700
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-05 12:05 -0700
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-05 12:14 -0700
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-05 12:36 -0700
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-05 14:11 -0700
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-06 09:35 -0700
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-06 11:04 -0700
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-06 18:07 -0700
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-11 15:35 -0700
                Re: Bell's spaceship paradox... kenseto <setoken@att.net> - 2015-09-05 06:12 -0700
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-04 11:34 -0700
                Re: Bell's spaceship paradox... pnalsing@gmail.com - 2015-09-03 14:51 -0700
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-04 11:11 -0700
                Re: Bell's spaceship paradox... pnalsing@gmail.com - 2015-09-04 11:14 -0700
                Re: Bell's spaceship paradox... mabel <wugi@scarlet.be> - 2015-09-04 20:52 +0200
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-04 11:14 -0700
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-04 12:53 -0700
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-05 22:52 -0700
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-06 09:42 -0700
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-09 15:07 -0700
                Re: Bell's spaceship paradox... pnalsing@gmail.com - 2015-09-09 15:33 -0700
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-11 09:08 -0700
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-11 12:52 -0700
                Re: Bell's spaceship paradox... Maciej Woźniak <mlwozniak@wp.pl> - 2015-09-11 22:45 +0200
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-11 15:16 -0700
                Re: Bell's spaceship paradox... Maciej Woźniak <mlwozniak@wp.pl> - 2015-09-12 12:10 +0200
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-11 13:55 -0700
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-11 15:13 -0700
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-13 09:19 -0700
                Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-13 14:01 -0700
                Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-14 09:12 -0700
    Re: Bell's spaceship paradox... Tom Roberts <tjroberts137@sbcglobal.net> - 2015-09-03 12:47 -0500
      Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-03 11:51 -0700
        Re: Bell's spaceship paradox... JanPB <filmart@gmail.com> - 2015-09-03 12:41 -0700
          Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-03 13:00 -0700
      Re: Bell's spaceship paradox... Maciej Woźniak <mlwozniak@wp.pl> - 2015-09-03 21:48 +0200
      Re: Bell's spaceship paradox... wugi <brol@brol.be> - 2015-09-07 18:30 +0200
        Re: Bell's spaceship paradox... Tom Roberts <tjroberts137@sbcglobal.net> - 2015-09-07 12:50 -0500
          Re: Bell's spaceship paradox... alsor@interia.pl - 2015-09-07 12:55 -0700
          Re: Bell's spaceship paradox... wugi <brol@brol.be> - 2015-09-12 17:17 +0200
  Re: Bell's spaceship paradox... John Gogo <jfgogo22@yahoo.com> - 2015-09-04 17:49 -0700
    Re: Bell's spaceship paradox... John Gogo <jfgogo22@yahoo.com> - 2015-09-04 19:09 -0700
  Re: Bell's spaceship paradox... rotchm <rotchm@gmail.com> - 2015-09-05 20:53 -0700

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