Well in the world of physics,time machine has a great discussion and why not. No one is clear behind the concept of time machine. What actually happens is all behind the ray of light which we see all around. Yes, time machine is a machine which uses the speed of light to enable us to see the past……. Lets take an example and decide how the grandfather died There was a boy whose grand father died 5 years ago in an accident and now the boy travelled past in a time machine and shot his grand father just before the accident. Now the question arises how the grand father died, in an accident or by the bullet his grand son shot. its indeed a big question with a very simple explanation…… Time machine does not take us in the past it just shows us the light of the past. Let me explain it a bit more. It is because of light that we are able to see and observe incidents and light ray of every incident remains forever. So when we are in the time machine it actually makes us move with the velocity of light and on that velocity we are able to catch the light of the incident of the past which we want to see. So by this we can say that if possible to travel with the velocity of light, we can witness the past incidents but cant influence them. so now we can evidently say that grandfather died in an accident and not by the bullet grandson shot.