"xxein" <xxein@bellsouth.net> wrote in message http://groups.google.com/groups?selm=cce403e3.0406151807.76ed6ff2%40posting.google.com...
> "Dirk Van de moortel" <dirkvandemoortel@ThankS-NO-SperM.hotmail.com> wrote in message http://groups.google.com/groups?selm=b5Vyc.154506%24_7.7565377%40phobos.telenet-ops.be...
> > "xxein" <xxein@bellsouth.net> wrote in message http://groups.google.com/groups?selm=cce403e3.0406121947.3a7ce897%40posting.google.com...
> > > "Dirk Van de moortel" <dirkvandemoortel@ThankS-NO-SperM.hotmail.com> wrote in message http://groups.google.com/groups?selm=QHbyc.152112%24Du4.7711898%40phobos.telenet-ops.be...
> > > > "xxein" <xxein@bellsouth.net> wrote in message http://groups.google.com/groups?selm=cce403e3.0406101804.425cde53%40posting.google.com...
> >
> > [snip]
> >
> > > > > Look, it's simple.  First they give a scenario that is UNDEFINED in
> > > > > SR.  There is no preferred frame. There is no way to define whether A
> > > > > or B or both are accelerating toward each other OR A and B are
> > > > > accelerating to an imaginary point C that is not on the line between
> > > > > them.
> > > >
> > > > "A" feels a constant acceleration. That can be measured with an
> > > > accelerometer - that is a real piece of hardware. It measures
> > > > something we call the acceleration with respect to the momentarily
> > > > comoving inertial frame of A. The meter reads the value a.
> > > > "B" feels no acceleration: his personal accelerometer reads 0.
> > > >
> > > > That's all that is needed to describe the situation. There is no need
> > > > for a preferred frame.
> > > >
> > > > Dirk Vdm
> > >
> > > xxein:  Yeah, I'm getting lazy.  I realised that after the post.  BUT
> > > does a painter feel acceleration when he falls off the ladder (ignore
> > > the atmosphere, please)?  What does his accelerometer read?
> >
> > He doesn't feel anything. His meter reads zero.
> > He and his meter will get a jerk when the ground hits them.
> > But you know that already. You shouldn't have asked this
> > question.
> >
> > >
> > > There is a missing component to CS's.  It is bridged in a mathematical
> > > fashion by inducing a curvature of spacetime.  It is not bridged in
> > > any other way.  Mathematics does not make physics.
> >
> > That is where most crackpots go berzerk: they see a square
> > root (*) and they think they can and should understand relativity.
> > In the best case they confuse the model with what it describes,
> > but most of them don't even know what coordinates are.
> >
> > (*) Some of them think that sqrt(4) can be -2.
> >
> > Dirk Vdm
>
> xxein:  (*) It can't?

That is truly incredible.
If you have to ask this question, how can you *ever*
have understood *any* equation involving a square
root in *any* textbook?
    sqrt(4) = 2
    -sqrt(4) = -2
    sqrt(x^2) = x for all x >= 0
    sqrt(x^2) = -x for all x <= 0
You are joking, right? :-)

Dirk Vdm