> Dave, you're the resident expert on space >travel.
> (Unless there are any other authorities on the
> subject that would like to speak up.) If you
> travelled through space at 10% the speed of
> light,
> do the effects of relativity (i.e., time passes
> more slowly for those doing the travelling)
> become significant?

Not really.

The relevent equation is

1
-------------------- = gamma
SQRT(1 - (v^2 / c^2)

Where gamma is the factor which determines the amount of time dilation.

In this example, where v = .1c, gamma works out to 1.006. The amount of time dilation in the frame of reference of the "stationary" (Earth-based) frame of reference is given by the factor of 1/gamma, which in this case is .994

So a journey taking 80 years as seen in the Earth-based frame would take 79.5 years in the frame of reference of the spaceship (if I've done all my calculations correctly.) A difference of only six months.

I leave it as an exercise for the reader to find out how fast you'd have to go in order to make the apparent ship time half of the Earth-based time for an 80 year journey. All answers should be expressed in terms of percentages of the velocity of light (c)

Those of you wanting to learn more can read the "Relativity and FTL travel" FAQ--there is a link to it from my writer's resources page.