Re: Is Lorentz contraction objectively real?

From: Tom Roberts (tjroberts_at_lucent.com)
Date: 09/13/04 

Date: Mon, 13 Sep 2004 14:15:05 -0500

Eugene Shubert wrote:
> The question is, Is Lorentz contraction objectively real?

That, of course, depends strongly on what you mean by "objectively real"
-- there is no objective meaning to that phrase (:-)).

When I carry a 2-meter long rod through a doorway that is 1 meter wide,
I must rotate it so its 2-meter length is not parallel to that 1-meter
aperture. Is that "objectively real" -- if so, then so is "Lorentz
contraction"; if not, then not. Note I did NOT shorten the rod in any
way, I merely rotated it to fit.

Nobody[#] ever expected that a moving rod "physically" contracts;
"Lorentz contraction" is merely a change in perspective between rod and
observer. But as that doorway example shows, such changes in perspective
can have physical consequences. For SR, the most notable is for "time
dilation", and the fact that short-lived particles can travel
considerably further in the lab than their speed times their proper
lifetime implies. This is a direct consequence of "time dilation", which
is another aspect of changes in perspective, and seems "objectively
real" to me.

        [#] Except for some people around here who don't understand
            SR at all.

Direct observation of "length contraction" is more difficult than "time
dilation". But the correspondence between fixed-target and
colliding-beam interaction and scattering cross-sections is a
demonstration of the validity of the Lorentz transform, and is directly
related to "Lorentz contraction" (transformation of solid-angles).

Eugene Shubert wrote:
>>>Lorentz contraction is just a peculiarity of a simplistic
>>>coordinate system that physicists believe in.
Tom Roberts replied:
>>It's far more than mere "belief" -- these are the coordinates used
>>in essentially every laboratory on earth. And in myriad engineering
>>projects. And by anyone who thinks very much about it at all --
>
>
> Right. And the question is, How could there ever be objectively real
> experimental evidence demonstrating that Lorentz contraction is real
> without equally compelling experimental evidence that nature favors
> E-synchronization above ~S-symmetry?

I was describing your sliiy claim about "belief in coordinate systems",
not "belief in Lorentz contraction".

Do you also claim that "time dilation" is not "objectively real"?
   If so: how is it that pion beams exist?
   If not: why not? -- they are two sides of the same coin (it's a
       many-sided coin, and includes that rod and doorway above)...

I think you are hung up too much on undefinable words (like "objectively
real")....

In an earlier thread you said:
> My thesis is that the Lorentz contraction is just as subjective as is
> simultaneity.

Of course it is! Geometrical perspective is ALWAYS subjective. As is
simultaneity (which is yet another side of the same coin).

That coin, by the way, is geometrical projection, aka perspective. It
arises in many contexts in physics.

> I've written a simple, flawless, easy to understand interpretation of
> the Lorentz transformation but can't get a single endorsement for it
> to be included in the physics.ed-ph section of arXiv.
> http://www.everythingimportant.org/relativity/special.pdf

I would not call that paper "simple and flawless" at all. The very first
sentence of the abstract shows quite clearly that the author does not
understand the modern vocabulary of physics.

> Relativity Lite is merely the most obvious interpretation of the
> Lorentz transformation

Somehow, imagining sliding rulers does not agree with "the most obvious"....

Tom Roberts tjroberts@lucent.com

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