Greetings from Croatia :) It may seem like a 100 times told story but it's not... Let us imagine that we have a rocket with length 50 m when at rest. The rocket goes on a trip and accelerates to the speed near c. Observer from Earth "measure" it's length as 48m (illustrative value),that is for the observer, rocket's length is contracted. But no matter what "exhibitions" rocket preforms at speed close to c and regardless of that length contraction, when rocket returns to Earth it will be of course 50 meters long and not 48. At the same time when length contraction occurs, observer from Earth "sees" that rocket clock is going slower than our clock and we also see all passenger's biological processes on that rocket as slowed down. Now, SR says that time for the man in that rocket goes normally and also observer's time on Earth goes normally.....so my question is, what causes different time accumulation on rocket's clock and on Earth's clock when these two clocks are compared after rocket returns on Earth ? (clocks are synchronized before the trip, and if there are any internal or external mechanical influences that can affect on process of generating seconds, they are subtracted from the result time) Upper question also imply - What is so special in speed of light that when rocket travels at speed close to c, traveling at that speed causes different biological age of two people (observer on earth and man in the rocket born on the same date when they are reunited after rocket returns to Earth) ? This is the point - if after rocket's return length remains the same regardless of our measurement of it's smaller length when it was traveling at speed close to c , what is the cause of different time accumulation and different biological age, that is, if the length remains the same, why the time accumulated on almost ideal clocks is also not the same but different? For now I still believe that time dilation and length contraction are real and at the same time apparent phenomena, that is, motion is relative and every frame of reference is equal so what one observes/measure is the true value but at the same time after rocket from the upper story comes back in our frame of reference time dilation and length contraction become apparent because length is the same as before the trip and the time should also be the same on both clocks, but maybe you can explain me why I'm wrong. I still haven't found a proper answer to these question/s. Thank you!!!