Time dilation in Joe Haldeman’s The Forever War makes sense. The closing you get to the speed of light then relative to other observers (e.g. those still on earth) time goes slower for you.
In effect, you are travelling to the future while those on earth are still passing through time on normal speed.
But I’m wondering: is there any way to reverse the effect? In particular, you can only go forward in time not backwards (according to Einstein special relativity). So that would mean the people on earth need to travel around the speed of light to match the two times (or meet a star with high gravitational effects).
Another interesting part is the effects of gravity seems to be like those of travelling close to the speed of light. I.e. getting close to a neutron star which high gravity like in interstellar.
The gravity of the neutron star causes time to slow down in comparison to those observers who are outside the gravitional effects of the star.
When travelling close to the speed of light, in effect there is the effects of gravity anyway. According to Newtown’s law one force will have an equal and opposite force.
So travelling close to the speed of light one way, we cause an equal and opposite force (which we can measure in terms of earth’s gravity).
These are some of tidbits I got from The Forever war.