First of all thanks for both answers... even if i did not read well ghwellsjr for now (it needs more time)
Let's see using lorentz equations (c=1):
T1' = γ ( T1 + v d) in the first flight
T2' = γ ( T2 - v d) in the back flight
d=cT/2 i.e. T/2 and T1=T2=T/2
2d' = cT' = T1'...
First: thanks for reading
Second: I'm not interested in other "experiments" that prove contraction of lengths (i know them and i know it works)
Third: Please find where is the problem in my simple thought
Let be a "rest frame" S with an object to measure its length and do it with a ray of...