There is a circularity in the idea of measuring the speed of light: to measure the speed you need synchronized clocks; but you can't get distant clocks synchronized unless you know the speed of light. It's a logical circle. The only way out of it, says Einstein, is to assume (stipulate) that the...
So he made the assumption
This puts it in the wrong light. Einstein was quite explicit: the constancy of the speed of light is not an assumption (an hypothesis or an empirical generalization). It is a bit of logic that has to do with the only possible way of synchronizing (distant) clocks and...
Actually I was imagining the case where the two rays of light were emitted in opposite directions at the same time at the same place where the balloon is. They are reflected off equidistant mirrors and arrive back at the same place where the balloon is at the same time, and the balloon explodes...
I am reminded of Shroedinger's Cat that is only "probably alive or dead" because it is connected to a lethal device that kills if and only if a sub-atomic particle travels to a certain position or is emitted at a certain time, which quantum events have only a probability of occurring.
I'm an...