The Bell Rockets

Considerable effort is devoted to show how space and body differ in relativity. We consider the example of two rockets set in motion in synchronous way, connected by a fragile thread; rockets are allowed to move faster and faster: while spatial distance of rockets remains unchanged, the Lorentz-contracted thread breaks. We show that one can record the history of contraction effects just like one does with the time dilation effect measuring time using a clock; this allows us to design a body-contraction measuring device.