The *really* interesting thing about Flight of the Navigator
was the concept that the boy did not age
(well, he did, but an undetectable four hours) because the majority of his 8 missing years were spent travelling at (or near) light speed
! Of course this was due to the time dilation
experienced by matter travelling near C
, as explained in the Special Theory of Relativity
. Pretty heavy concept for a kids' movie
to be based on. To be honest though, I can't remember how explicitly this was addressed in the movie. And of course they kind of copped out, letting him go back
in the end... I suppose tachyons
were somehow involved...
Addendum: According to the "Relativity Calculator" (http://www.1728.com/reltivty.htm) the Navigator's travel speed was 0.9999999983710723 * C, or 299792.45751165977 km/sec. That's assuming that the ship accelerated instantaneously (a dubious prospect) and maintained the same speed afterwards.