http://www.fourmilab.ch/etexts/einstein/specrel/www/
ON THE ELECTRODYNAMICS OF MOVING BODIES
By A. Einstein, June 30, 1905
"We will raise this conjecture (the purport of which will hereafter be
called the "Principle of Relativity'') to the status of a postulate,
and also introduce another postulate, which is only apparently
irreconcilable with the former, namely, that light is always
propagated in empty space with a definite velocity c which is
independent of the state of motion of the emitting body. (...) Any ray
of light moves in the "stationary'' system of co-ordinates with the
determined velocity c, whether the ray be emitted by a stationary or
by a moving body. (...) From this there ensues the following peculiar
consequence. If at the points A and B of K there are stationary clocks
which, viewed in the stationary system, are synchronous; and if the
clock at A is moved with the velocity v along the line AB to B, then
on its arrival at B the two clocks no longer synchronize, but the
clock moved from A to B lags behind the other which has remained at B
by tv^2/2c^2 (up to magnitudes of fourth and higher order), t being
the time occupied in the journey from A to B. It is at once apparent
that this result still holds good if the clock moves from A to B in
any polygonal line, and also when the points A and B coincide. If we
assume that the result proved for a polygonal line is also valid for a
continuously curved line, we arrive at this result: If one of two
synchronous clocks at A is moved in a closed curve with constant
velocity until it returns to A, the journey lasting t seconds, then by
the clock which has remained at rest the travelled clock on its
arrival at A will be tv^2/2c^2 second slow."

This is a biased scenario presenting onesidedly the RECIPROCAL time
dilation. A non-biased scenario:

"...at the points A and B of K there are stationary clocks which,
viewed in the stationary system, are synchronous." The front end of a
very long train "is moved with the velocity v along the line AB to B."
All along the train there are synchronous (viewed in the system of the
train) clocks which, on the arrival of the front end of the train at B
(the back end has not reached A yet), stop both ticking and moving
"with the velocity v" simultaneously (simultaneity defined in the
system of the train).

If Einstein's 1905 constant-speed-of-light postulate is true, then a
clock at the front end of the train lags behind the stationary clocks
at A and B. This is established by both observers (the stationary one
and the one in the train) after clocks in the train have stopped.

On the other hand, if Einstein's 1905 constant-speed-of-light
postulate is true, then the stationary clock at A lags behind all
clocks in the train, the clock at the front end of the train included.
This is established by both observers (the stationary one and the one
in the train) after clocks in the train have stopped.

Clearly we have REDUCTIO AD ABSURDUM showing that Einstein's 1905
constant-speed-of-light postulate is false.

Pentcho Valev