Physically, the Earth doesn't travel at -v wrt the rocket. 
Imagine yourself sitting on the Moon, looking at the Earth and 
at the rocket. 
Clearly, you see the rocket moving away from the Earth, not the 
contrary.
-v is a pure geometrical abstraction, which leads to the wrong
conclusion that, from the point of view of the rocket, clocks on the 
Earth appear to be running slow by a factor sqrt((1-(v/c)^2), and
from the point of view of the Earth, clocks on the rocket appear
to be running slow by the same factor.