"It’s pretty hard to get to another star system. Alpha Centauri is four light years away, so if you go at 10 per cent of the speed of light, it’s going to take you 40 years, and that’s assuming you can instantly reach that speed, which isn’t going to be the case. You have to accelerate. You have to build up to 20 or 30 per cent and then slow down, assuming you want to stay at Alpha Centauri and not go zipping past. It’s just hard. With current life spans, you need generational ships. You need antimatter drives, because that’s the most mass-efficient. It’s doable, but it’s super slow."
— Elon Musk