time dislocation

A major drawback in exploiting the effect of time dilation to achieve manned interstellar flight is that those who make the journey age less than those, including friends and family members, who remain behind. For very long journeys at high fractions of the speed of light, the time dislocation may be so great that many generations, and even millennia, may pass on the home planet before the interstellar travelers return. For example, an excursion from Earth to Rigel, 900 light-years away, and back, at (a constant) 99.99% of light-speed, would take 1,800 years as measured on Earth but only about 28 years as experienced by those on the spacecraft. It had been argued, for example by Sebastien von Hoerner, that such acute time dislocations – effectively hurling the travelers into the future – will prevent interstellar travel beyond a few tens of light-years and, therefore, the colonization of the Galaxy. However, there may be other ways to circumvent the light barrier.