Originally posted by Bannanafish
ok ok
EXPLANATION!!!
Acceleration of the spaceship, taking time for the astronaut to "see" the clock on earth, and any other "complications" are all irrelivant. This is a THOUGHT experiment, hence ignoring all these factors. Hell, if it weren't i'd argue how the hell could the astronaut see a clock so far away?? Also in Einstein's THOUGHT experiment, he never said anytihng about acceleration (which is obviously needed for his trains to travel so fast).
So since we can ignore all these things, think of the spaceship as a train.
Train is travelling at 0.8c
Goes past an observer
Observer looks in the window of the train and the clock inside is running slow (i.e. for every second on his watch, the clock is only going a fraction of a second)
The passenger on the train looks at the observer's watch and sees it as going slow (i.e. for every second on his clock, the watch is only going a fraction of a second)
If the observer sees something to take 10 seconds according to his watch, then he sees the clock inside the train go 6 second.
If the passenger sees something to take 10 seconds according to his clock, then he sees the watch on the observer to go 6 seconds.
Now if 10 seconds was 10 years, the PASSENGER'S clock READS 10 hours. THIS IS WHAT THE QUESTION GAVE YOU.
Now the PASSENGER looks at the OBSERVERS watch. THIS IS THE PERSPECTIVE THE QUESTION ASKED.
Therefore the OBSERVERS watch would say 6 years have passed.
Now if you can't understand this, i don't see how you can argue.