I am pretty familiar with the theories of special and general relativity. I know how to add velocities, I know the main postulates and the experimental confirmation. However, I thought of the following thought experiment: There are 3 experimenters (at the same point in space), who adjust their clocks at time point 0. Two of them get into their spaceships and travel in opposite directions at a constant speed close to the speed of light (for example 0.75c). Once they travel a certain distance measured by their clocks (both travel with a constant speed of 0.75c) they launch probes traveling back to the third experimenter - he is now exactly in the middle. Lets assume that each probe travels again with a speed of 0.75c towards the third experimenter left in the middle. Lets assume that at a given time he can observe only one of the probes traveling towards him (as if the other probe doesn't exist at all). Then he would measure that this one probe approaches him with 0.75c. Then, he does the same measurement with the other probe and finds out the same - that it approaches him with a speed of 0.75c. Why the hell then the two probes will approach each other with a speed of 288010km/s instead of 450000km/s? This system could be regarded either as two separate systems (experimenter 3 + probe 1 and experimenter 3 + probe 2) or as one system (experimenter + probes 1 and 2). Note that this experiment doesn't change the reference frame. It also takes care of the simultaneity and is completely symmetrical. Why the probes don't approach each other with 1.5c? Further speculation: If the third experimenter stays where he is, he may get killed (and thus live a shorter life) by the two probes approaching him with a speed of 225000km/s (0.75c) when measured individually, compared to the case in which each of the probes approaches him with a half of their combined speed 288010/2=144005 (according to the theory of relativity). Please help with a reasonable explanation. This for me is a paradox that I can't resolve.