Synchronising clocks Referring to fig 1 I want to synchronise two clocks. I have a space ship travelling at v in the direction of the arrow. In the ship I have two identical clocks one at point A (clock1) and on a point D(clock 2). I also have a light source at point B. Length AB = length BD I have observers at points E, F, G and H. E and F are at rest with the space ship. G and H are not at rest. A flash of light is set of by the light source and if it hits both clock simultaneously then they are synchronised. As the light from the light source is travelling perpendicular to the direction of travel of the space ship the light will reach both clocks simultaneously and they’ll be synchronised. I will look at what the observers see later. Fig 2 shows how NOT to synchronise clocks as the clocks are equidistant and as they will change position before the flash of light reaches them then the flash will not reach them simultaneously and they will NOT be in sync Does anyone disagree ? So I sync two clocks using the method in fig 1 Referring to fig 3 I want to move the clocks, one to the front of the space ship and one to the back and I want them to still be synchronised from the perspective of the observer at E. The velocity of the space ship is V. I move clock 1 from point A to point A hat at velocity V1. I move clock 2 from point D to point D hat at velocity V2. The length from point D to the point D hat is equal to the length from point A to point A hat. There is an observer at E Depending on the velocities that the clocks are moved at the observer will see the following: 1. If V1 = V and V2 = V Clock 1 will be stationary, clock2 will be moving at 2V. therefore clock 2 will slow down clock1 will be ahead of clock 2 2. If V1 > 2V and V2 = V Clock 1 will be moving faster than clock2. Clock 1 will slow down wrt clock2. Clock 2 will be ahead of clock 1 If V1 < V and V2 = V Same as 1 If V1 = V and V2 < V Same as 1 If V1 = V and V2 > V Same as 1 If V1 = X and V2 = V - X Both clocks moving at same speed therefore they are synchronised If V1 = c and V2 = c As both clocks are move at C both will stop and they will be synchronised when they make it to their final destination. Does anyone disagree ? I will do what the observer in the space ship sees next as this gets complicated.