A quick response...
Nathan asked..."What is it that makes mine different from yours if we are at the same precise time and place, yet viewing different realities?"
Perception and past experiences can all create a different "take" on nearly any event (reality) no matter how many people see it.
You could have a valid point with the Nagasaki comment though. Except what might have been going through each individuals mind during that millisecond. Those are still theirs and theirs alone.