Hi everyone, before I post I apologize for my bad English! I am not a physicist but I am interested in this stuff (I've read relativity theory and...) But I have a question regarding time traveling Imagine that it is true that we can travel at speed of light...So here is the famous example of identical twins: one of whom makes a journey into space in a high-speed rocket and returns home to find that the twin who remained on Earth has aged more. it could be that, aboard the space-ship, two years of flight-time have passed - on-board clocks and calendars show that two years have elapsed, and both spaceship and travelling twin have aged by exactly that amoung of time. On Earth, however, a whopping 30 years have passed between the spaceship's departure and its return. Just like all other humans on the planet, the twin on Earth has aged by 30 years during that time. So here is my question: Does the brother who was on the space looks younger? I mean his face? is it true that one of them looks like a child while the other one looks like an adult? Does biological ageing like growing cells and chemical reactions in our body go slower like time? Or it is just a matter of relativity meaning that they just had different experience of time and both of them are look the same regarding their face and body?