Carl Sagan discussed this in episode 8 of Cosmos. This segment of video[1] progresses from Leonardo DaVinci's flying machines to a relativistic space craft in a

Carl Sagan discussed this in episode 8 of Cosmos. This segment of video[1] progresses from Leonardo DaVinci's flying machines to a relativistic space craft in about 7 minutes. A spacecraft accelerating at 1 g, closer and closer to c, accelerating halfway and decelerating halfway, could travel to Barnard's Star in 8 years ship time; center of the Milky Way Galaxy in 21 years ship time, the Andromeda galaxy in 28 years ship time. "In principle such a journey, mounting the decimal points closer and closer to the speed of light, would even permit us to circumnavigate the known universe in 56 years ship time. We would return tens of billions of years in the far future, with the Earth a charred cinder, and the Sun, dead. Relativistic space flight makes the universe accessible to advanced civilizations, but only to those who go on the journey, not to those who stay home." https://www.youtube.com/watch?v=abp3q7aYOss&feature=youtu.be&t=1600 https://www.youtube.com/watch?v=abp3q7aYOss&feature=youtu.be...