Re: The relativity of the distance.


Dirk Van de moortel wrote:
"Stamenin" <tasko.s@xxxxxxxxxxx> wrote in message news:1163303696.738981.74800@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx


.THE BEHAVIOUR OF MEASURING-RODES AND CLOCKS IN MOTION

In page 37 0f his Relativity Einstein writes about the relativity of
the distance. There is very strange conclusion that the distance
becomes smaller when the speed v tends to the light speed c.
He takes as a base the relation of the Lorentz transformation:
x'=( x-v.t)/R which gives the distance x' in K' (train) when we
know the x and t in K (embankment). Here is what Einstein says in his
book:
"I place a metre-rod in the x'-axis of K' in such manure that
one end (the beginning) coincides with the point x'=0, whilst the
other end (the end of the rod coincides with the point x'=1. What is
the length of the metre-rod relative to the system K? In order to learn
this, we need only ask where the beginning of the rod and the end of
the rod lie with respect to K at a particular time t of the system K.
By means of the first of the Lorentz transformation the values of these
two points at the time t=0 can be shown to be:
x(beginning of the rod)=0.R
x(end of rod)=1.R
R being the squares root of the Lorentz transformation"..
In this way he finds that the distance between the points is
D=R=(1-v^2/c^2)^0.5.
When v=c, the distance D=0.
For me is very strange that nobody observed that the rod gets in this
case an infinite mass and a volume zero!!!
On the other hand the above relation is wrongly used. The real
relation which is valid for this case and allows us to resolve this
problem, is the following:
x=(x'+v.t')/R.
So the distance D becomes bigger and for v=c distance should have an
infinite value. That means that if the train travels with speed c the
two ends of the rode should be one in the infinite and one still here
near us.
This could be a real possibility, isn't it?

No, it couldn't, because when you use this equation, you
measure both end points of the rod simultananeously in the
K'-frame, with both t' = 0, which means that you don't
measure the distances at the same time in the K-frame,
so you get nonsense.

If you measure the distance of the front of a moving train
now and the distance to the back 10 minutes later, is the
difference between those distances the length of the train?
No, you just get a useless number.

That is why the other equation is used. The presence of t
allows the measurements of the distances to cancel, if the
values for t are the same (for instance t = 0).

By the way, the concept of relativistic mass is old fashioned:
http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.html
Forget about it.

Dirk Vdm


In my topic I show two deficiencies of the Einstein theory:
1) The first is that Einstein uses the wrong relation for his
demonstration that the distance becomes small by making the v tending
toward c and for v=c the distance becomes zero. For this question none
of you has given any answer.
2) In the second deficiency I use the right Lorentz relation and it
gives for v=c, an infinite length.
I got for my topic four different answers from four persons. All of
you practically said that the result obtained with the use of the
Lorentz transformation is not correct. By this you indirectly said that
Einstein theory of the relativity do not corresponds for the
description of the motion of the material bodies.
I just intended to write about this very important topic by numerating
all the deficiencies that I have mentioned until now. Maybe is better
to separate these two theories, the Newton's for the description of
the motion of the material bodies and the Einstein's for the
description of the laws of the physics.
12/12/2006.

.

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