Re: So... Lerentz Contractions are *physical* not observered?

On Jul 4, 4:23 am, "Bill Hobba" <rubb...@xxxxxxxx> wrote:
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On Jul 3, 3:24 pm, "Jeckyl" <n...@xxxxxxxxxxx> wrote:
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On Jul 3, 6:01 am, Tom Roberts <tjroberts...@xxxxxxxxxxxxx> wrote:

[...]
Lorentz "length contraction" is similar: the invariant length of an
object is GEOMETRICALLY PROJECTED onto a coordinate system, and
depending on orientation the projected value of that length can be
less
than the invariant length of the object (the invariant length of an
object is its length in its own rest frame).

So the object does not get "physically" any shorter (i.e. its
invariant
length remains constant), but the orientation between object and
coordinates used for measurement can have "physical" consequences
(i.e.
one obtains a different value for the length, the pole can fit into
the
barn in a famous gedanken, etc.).

[..]

Greetings, apologies for my indiscriminate snipping.

I have a semantic argument with this claim that an object does not get
"physically" any shorter (why the quotes?).

If I measure an object to be 80m, using the physical definition of
length, isn't that object physically 80m? Am I incorrect to say the
physical length of the train as measured from the rest frame of the
tracks is 80m?

Of course we agree the object remains 100m as measured in its own rest
frame, but does that mean that Lorentz contraction is somehow not
physical?

Perhaps the answer is similar to the reason why the Coriolis force is
often called "fictional", despite the very real physical effects.

Thanks -

I think the point is whether the proper length of the object changes or
not.
In SR it doesn't change .. its projection in other frames of references
is
shorter .. but the object itself isn't.

I think also "physical" implies some change to the object itself.

For example in Lorentz theory, there is physical contraction (objects
get
physically shorter .. ie their proper length changes) when objects move
in
the absolute ether frame ..

I don't think that's accurate. The length of an object as measured
from the ether rest frame changes when that object is in motion, yes.

Yes

However, the Lorentz interpretation agrees with standard SR that the
length of an object as measured in its own rest frame does not
change.

That what I said .. BECAUSE the rulers by which we measure it have ALSO
changed in their absolute length

If this is what we mean by proper length, and what else could
we mean, then the proper length doesn't change.

In Lorentz theory, the proper lenth is the rest length in the absolute
ether frame .. that we a fooled into seeing the same length in other
frames is due to the physical contraction and time dilation etc that
occurs due to movement wrt that ether frame

but because all the rulers comoving with the
object change by the same amount, the measurement of it in its rest
frame
appears to be the same. That's pretty much the opposite to what SR says
happens.

I don't see much of a difference. Both say the proper length stays
the same.

No .. in Lorentz the ONYL things that have their proper length are those
at rest in the ether frame .. everything else is physically contracted and
clocks slowed, so that they only appear to be their proper length, but are
not physically the length we measure them

Both say the length of the train as measured by the radio
switch operator will be shorter. Isn't this the same theory we are
talking about?

Yes .. both will give the same results .. its how you interpret what is
meant by real and physical.

In SR, every iFoR has the objects at rest in it truly at their proper
length .. there is no contraction or time dilation.
In Lorentz theory, only the ether iFoR has the objects at rest in it truly
at their proper length .. there is no contraction or time dilation. Every
other iFoR has physical contraction and dilation, but has an illusion of
proper length and time.
The thing is, we cannot tell one from the other by making measurements etc
.. they both give the same result.

I would like to expand on this comment. While experimentally we can not
tell the difference apply LET to create Quantum Field Theory would be so
silly no one would even consider it. The basis of QFT is Lorentz invariance
which fit naturally into SR - not LET. BTW Tom was the first to make me
aware of this - so again thanks to Tom.


Hi Bill-

I'm not sure I understand. Isn't Lorentz invariance a property of
our metric which can be explained and derived from LET? I thought
that the predictions of LET are explicity Lorentz invariant. The
"rest frame of the aether" is just another inertial frame of reference
like any other, perhaps useful for some calculations but not necessary
and as Einstein said "superfluous".

If we can't tell the difference between SR & LET, why would one be
silly and the other not silly? I am not a quantum field theorist,
sorry, so please enlighten me as to why special relativity as derived
from a mechanics of the space-time medium would cause problems in
QFT.








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