Re: Is Lorentz contraction objectively real?

From: Androcles (androc1es_at_nospamblueyonder.co.uk)
Date: 09/25/04 

Date: Sat, 25 Sep 2004 13:15:41 GMT

"Eric Baird" <eric_baird@compuserve.com> wrote in message
news:4oj9l0t58tomuueik7gc1mmthu7o8ooq6s@4ax.com...
| On Sat, 11 Sep 2004 13:36:02 -0500, "Eugene Shubert"
| <http://www.everythingimportant.org> wrote:
|
| >Those who teach special relativity consider it a very important
| >exercise to have students decide how to measure the length of
| >a rapidly moving object. That's religious indoctrination and a
| >wrongheaded approach to physics. The theoretical process
| >that physicists talk about to measure the length of a rapidly
| >moving object requires belief in simultaneity. In actual reality,
| >according to the math of relativity theory, simultaneity doesn't
| >exist.
| >
| >Lorentz contraction is just a peculiarity of a simplistic coordinate
| >system that physicists believe in.
| >
| >http://www.everythingimportant.org/relativity/special.pdf
| >
| >Eugene Shubert
|
|
| [1] If we assume that light propagates preferentially in our own
| frame, then when we view a receding (or approaching) rod, it will
| appear redshifted (or blueshifted), and will appear to contract (or
| elongate) by a ratio that exactly matches the ratio by which its light
| is seen to be frequency-shifted.
| With v quoted as recession velocity, that ratio comes out as :
|
| :[1] : len'/len = freq'/freq = c/(c+v)

Err..... freq = 1/time
c = len/time = len*freq

Hence len'/len = freq'/freq = (c+v)/c

|
| So a receding object appears shorter and an approaching object appears
| longer. You can work out the above ratio by working out the different
| signal flight-times from the different parts of the rod to the
| observer, and taking into account how far the rod's position changes
| while those signals are in flight. You can think of it as a simple
| optical effect.
| I think that it was Penrose who referred to this apprent visible
| change in length as something like "the spatial analogue of the
| Doppler effect"
|
| ----------
|
| [2] If we now repeat the same exercise, but this time assume that
| the light-signals propagate at a definite fixed speed wrt the /rod/,
| we again get the result that the receding rod is seen to be redshifted
| and contracted and the approaching rod is seen to be blueshifted and
| elongated, but the calcualted ratio comes out a bit differently.
| The frequency-change and length-change effects still precisely agree,
| but now they obey the rule:
|
| :[2] : len'/len = freq'/freq = (c-v)/c

Correct.

|
| ------------
|
| [3] If we now move on to special relativity, SR "relativises" both
| previous conflicting sets of calculations by saying that we should be
| able to claim with equal validity that the speed of light is "really"
| fixed wrt /either/ frame, and get the same final agreed physical
| predictions (for frequency /and/ depth), ragardles sof the choice of
| preferred frame
|
| So to achieve this, special relativity has to use an exactly
| intermediate prediction, which lies on an exact ratio between [1] and
| [2], which we can get to by multiplying [1] and [2] together and
| square rooting.
| This gives
|
| :[3] : len'/len = freq'/freq = SQRT[ (c-v) / (c+v) ]
|
| , which is pretty much the form given by Einstein in the 1905
| electrodynamics paper.

And wrong.
Androcles.
|
| --------------
|
| [4] This new prediction is engineered to depart from both [1] and
| [2] by exactly the same ratio, and if we decide that [3] is right, but
| that light propagates at fixed speed in a particular frame (freely
| chosen), then we can apply that "special" correction factor on top of
| the explicit propagation effects, to get to our agreed final answer
|
| That "rooted discrepancy" ratio, the square root of
| " [2] / [1] " , turns out to be the Lorentz ratio:
|
| : len'/len = freq'/freq = SQRT[ 1 - vv/cc ]
|
|
| Similar consioderations apply for transverse-moving objects
| ... where [1] is associated with a null transverse shift, and [2] is
| associated with a Lorentz-squared transverse redshift ("aberration
| shift"), SR predicts an intermediate, single, Lorentz redshift.
| For distances, one has to be extremely careful about how one defines
| "transverse" distances, but you get the same pattern, SR predicts
| apparent lengths in a photograph that are the root product average of
| what we would expect by assuming [1] and what we would
| l expect by assuming [2].
|
|
| -------------
|
| So, "SR photographs" ought to show a visible contraction compared to
| [1] ...
| So in /that/ sense, the contraction is a "photographable" effect.
|
|
| ... but we have to remember that the visible contraction is
| "interpreted", because the very same SR photographs can also be
| interpreted as showing a Lorentz /elongation/ compared to the
| "redder", "shorter" predicitons of [2], if light was supposed to
| propagate preferentially in the object's frame.
|
|
| ==========
|
| Since [2] also corresponds to the predictions made by Newtonian
| emission theory, one could perhaps argue that if the SR Lorentz
| effects are going to be considered as being "real", then we might end
| up claiming that Newtoinian theory predicts equally "real"
| contractiuon and time dilation effects, which are actually stronger
| than the SR predictions.
|
| Of course, nobody seems to reckon that it's /sensible/ to interpret
| the older Newtonian predictions as being split into a propagation
| component given by [1] and a "real" Lorentz-squared contraction and
| time dilation ... that normally looks like a very artificial and
| awkward thing to do ...
| ... but mathematically, those relationships /are/ buried in there in
| Newtonian theory, so if we are designing an experiment to isolate and
| verify the existence of the "new" SR time dilation and
| length-contraciton effects, we have to remember that our clever
| isolation techniques will be expected to find and report back a
| similar (but stronger) effect if the experiment obeys Newtonian theory
| instead of SR.
|
|
| Regards,
| =Erk= (Eric "I have chocolate trees in my bedroom" Baird)
|

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