They mention this in the paper: > Such a craft accelerating at a constant 1000 g for half of the trip and decelerating at the same rate for the remaining half

They mention this in the paper: > Such a craft accelerating at a constant 1000 g for half of the trip and decelerating at the same rate for the remaining half would reach the Alpha Centuri system within 5 days’ ship time due to the fact that it would have been traveling at relativistic speeds for most of the trip. However, for those of us on Earth, the trip would take over four years.