thanks for the answer Janus, very helpfull although it open the door to another tricky question.
a question that probably is more philosophical and speculative that scientific.
i getting a bit deeper into the matter and i noticed that many of the experiments, if not almost all of them, to confirm the time dilation predicted by the theory of relativity use the Doppler effect.
An effect which we could "feel" with our senses, hearing and sight, before it was scientifically "discovered" and explained.
so now i am wondering.
What if time rather than being the 4th dimension as we consider it now, it is actually a 6th sense. (not in the "classical" o Shamalayan way). which actually would cut the "possibility" of travelling in time, since it is not a dimension.
i mean with our five senses we take notice of changes. in radiation with the eyes, in air pressure with the hears, in surface texture with the skin, ecc.ecc.
i just throw it as an idea if anyone is interested in developing it, but as i said i know is more philosophical than scientific.
i should first demontstrate that we have an organ that register the change in "state" of the universe around us. a change that we call time.
but i have no intention in studying biology.
thanks again