The center of our galaxy is approximately 30,000 light years from us.
If we could accelerate a ship to close to the speed of light you could travel there in approximately 40 years ship time,depending on how close you got. However 30,000 years would have passed on Earth.
Theoretically with dramatic changes in technology on Earth over a 30,000 year span, mankind could have found a way to travel to the center of the galaxy, creating a civilization that had not only flourished but died off, before the original craft reached it's goal. Where a 20 year old original explorer was now only in his 60s.
Silly of course but...