We have two airplanes passing each other at high speed. The planes are the same length. We will call the airplanes A and B. The planes are passing each other at a speed close to the speed of light.
Here is the view from airplane A at rest...
Here is the view from airplane B at rest...
Both of these views are from the moment that the nose of airplane A reaches the tail of airplane B.
This must be the same moment in time between both frames of reference because there is only one moment
in time when the nose of airplane A is lined up with the tail of airplane B. If it isn't the same moment in time then the nose of airplane A passes the tail of airplane B more than once, which of course is nonsense. At this moment, the observer at T on airplane A looking down sees space and the observer at N on airplane B looking up sees airplane A, according to airplane A. At this moment, the observer at T on airplane A looking down sees airplane B and the observer at N looking up sees space, according to airplane B. We obviously have a contradiction. We have a paradox. Both situations can't simultaneously be true.
Here is the view from airplane A at rest...
Code:
T--------------------------------------N airplane A
<------- N-----------------T airplane B
Code:
T-------------------N -----> airplane A
N-------------------------------------T airplane B
Both of these views are from the moment that the nose of airplane A reaches the tail of airplane B.
This must be the same moment in time between both frames of reference because there is only one moment
in time when the nose of airplane A is lined up with the tail of airplane B. If it isn't the same moment in time then the nose of airplane A passes the tail of airplane B more than once, which of course is nonsense. At this moment, the observer at T on airplane A looking down sees space and the observer at N on airplane B looking up sees airplane A, according to airplane A. At this moment, the observer at T on airplane A looking down sees airplane B and the observer at N looking up sees space, according to airplane B. We obviously have a contradiction. We have a paradox. Both situations can't simultaneously be true.