Re: The reasons why SR is an aether theory


kenseto wrote:
> "PD" <TheDraperFamily@xxxxxxxxx> wrote in message
> news:1137171803.490873.10430@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > kenseto wrote:
> > > "PD" <TheDraperFamily@xxxxxxxxx> wrote in message
> > > news:1137078558.521961.49830@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > > >
> > > > > observer considers himself to be at the origin
> > > >
> > > > Correction: This is *sometimes* done, but by no means generally.
> > >
> > > There is no value to consider other point as origin.
> >
> > Don't be dense. The origin may be at a surveyor's mark, for example, or
> > it may be at the center of a nearby star (where the observer is
> > unlikely to be). The point is, convenience from the perspective of the
> > observer is *not* a solid argument for *physical* preference of a
> > choice of coordinate system.
>
> The point is: there is no need for any coordinate system. The observer
> assumes himself to be at the origin and at rest and all the objects are
> moving wrt to him. Then he uses SR or IRT equations to do the calculations.
> BTW, this assumption is the reason why SR is incomplete.
> >
> > > >
> > > > > and the coordinate axes are
> > > > > emanating from him.
> > > >
> > > > And how does he decide which direction is which?
> > >
> > > He can consider the line joining him and the observed object as the
> x-axis.
> >
> > He can, but he doesn't need to. Moreover, if there are more than one
> > observed object, this could raise real problems. The point once again
> > is that convenience for the observer does not indicate a *physical*
> > preference for choice of coordinate system. In fact, the arbitrariness
> > of the choice is precisely what's important in the physics.
>
> There is no problem at all. The SR equations do not require a coordinate
> system.
> >
> > > But we don't need this anyway. We just go ahead and use the SR or IRT
> > > equations to do the calculations.
> >
> > You'll note that the SR equations (at least as you know them) rely on a
> > choice of coordinate system. They are in fact transformations from one
> > *choice* of coordinate system to another *choice* of coordinate system.
> > But perhaps you don't get that.
>
> NO....The Sr equations do not rely on a coordinate system. The observer
> assumes that his coordinate is (t, x) and he uses the transform equations to
> determine the observed coordinate of (t', x')

Lookie there! A transformation of coordinates! And you say this can be
done without a coordinate system?? Do tell!

> > > >
> > > > In fact, the choice is arbitrary, which is precisely my point. There
> is
> > > > no particular *physical* preference for the arbitrary choice you
> > > > suggest. In fact, what's interesting about the physics is that it's
> the
> > > > same regardless of the arbitrary choice -- this seems to be the
> physics
> > > > that escapes you.
> > >
> > > The physics that eacapes you is that there is no need to make any other
> > > choice other than the observer himself.
> >
> > This is simply wrong. A physical argument based on observer convenience
> > is not physics. You have a highly limited understanding of what a
> > coordinate frame is, and what physics says about the choice that is
> > available in those coordinate frames.
>
> I repeat there is no need for any coordinate system.
> >
> > > When an observer asserts himself to
> > > be at rest his assertion is based on incomplete physics.
> >
> > Certainly. And *no* observer asserts himself to be at rest, except
> > possibly *with respect to* one of many possible choices of reference
> > frame.
>
> This is a stupid and circular statement. The observer is in relative motion
> wrt objects that are not at rest in his frame of reference so for you to say
> that he is at rest wrt these objects is extremely stupid. If you are saying
> that he is at rest wrt an object in his frame (not moving wrt him) then this
> is the same as saying that he is at rest wrt himself.....a circular
> arguement.
>
> >I don't know where you get the ridiculous notion that an
> > observer asserts himself to be at rest in SR. Where the heck did you
> > read up on SR, anyway?
>
> How about the SR statement: "in the rest frame of the observer, the clock or
> the rod"?????????

That's an incomplete thought, so it's a little hard to react to that
out of context. Perhaps if you identified where this reference came
from...

> >
> > > This incompleteness
> > > applies to every observer who considers himself to be at rest..
> > > > I did. And what makes you think that is a poor understanding of SR?
> > > > What authority or reference are you relying on for that judgement?
> > >
> > > Because Lorentz contraction is from the perspective of an observer. If
> > > contraction is real then there must also be expansion. Why? because when
> > > a rod returns from a journey it will have the same length as before the
> > > journey.
> >
> > Only if it is brought to rest in that reference frame. If it goes
> > blasting on by at the same speed at the end of a journey (think of a
> > runner running across a finish line), it will still be shorter.
>
> That's the point. That means that if length contraction is real then length
> expansion is also real. If that is the case how come SR doesn't have any
> equation to account for the fact that an observed rod might be length
> expanded compared to the observer's rod????

Because the equation refers to a *status* (the result of a
measurement), not a *process*. Let's identify the steps.
1. The rod is stationary in the frame in which the observer is also
stationary. A measurement of the length is made. The result of this
measurement is L.
2. The rod is accelerated.
3. The rod is moving in the frame in which the observer is stationary.
A measurement of the length is made. The result of this measurement is
L'.
4. The rod is decelerated.
5. The rod is stationary in the frame in which the observer is also
stationary. A measurement of the length is made. The result of this
measurement is L.

The length contraction formula relates L' to L (step 3 to step 1 or
step 5) and notes that L' < L always.
You seem to be focused on what's going on in step 2 (the rod's length
must be shortening), and in step 4 (the rod's length must be
lengthening). You are right about that, but the formulas that you are
referring to are referring to steps 1, 3, and 5.

>
> >
> > > So how come SR doesn't account for length expansion??
> >
> > It does, you goof.
>
> Where are the SR equations for length expansion of an observed rod?

See above.
You haven't far enough into SR to see the formulas for what happens
during acceleration and deceleration.

>
> >You are thinking about length contraction as being a
> > process that happens while something is speeding up. This *can* be
> > analyzed, but the basic SR notion that you're trying to deal with is
> > simply how something can be measured to be shorter *while it's in
> > constant motion* wrt to the observer. You have to understand what it
> > means to take a length measurement to understand how this happens, and
> > you have to do that before you worry about what happens while something
> > is speeding up and while it is slowing down.
>
> That's the perspective effect I was talking about.

You can call it perspective if you want to. It's real as real can be.
More importantly, there is no spatial length that is *more* real than
this.

> From a distance you
> appear to be shorter. But when you argued that length contraction is real
> then you are saying that length contraction is not a perspective effect.
>
>
> >
> > > Now do you
> > > see why I said that you don't understand SR?
> >
> > No, though it gets clearer day by day what you are misunderstanding
> > about SR.
>
> There is no misunderstanding.

I seem to have to correct you a lot for someone who understands it so
well.

> >
> > > >
> > > We use rod to measure length all the time. So if length is not a
> property of
> > > a rod then why are we using it to measure length????
> >
> > Sure we measure length. That doesn't mean its an inherent property of
> > the rod. It's a useful and real measurement that also happens to change
> > depending on the observer, even though nothing physical happens to the
> > rod.
>
> So now you are saying nothing happens to the rod. What happen to your
> assertion that length contraction is real????

You are too busy *attaching* the property length to the rod. They are
not so attached. The result of length measurement can change and this
be very real, and nothing physical happen to the rod.

PD

.

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