Hi I’m having a problem with a concept, well actually with a force. After watching a program about sending man to the other end of the galaxy in which a huge tube was created in where people lived and gravity was simulated by spinning it and producing Centripetal force. My problem is that I don't believe Centripetal is a single force, but more a tertiary force of gravity. In other words I thought physically that for Centripetal force to work you need gravity. I might not be making myself clear but if you just imagine a cylinder spinning in space there is no physical anchor to its inside. Basically if you lift your legs up or jump for instance other than a slight bit of air turbulence the cylinder floor would simply rotate under you because there is no connection via gravity or otherwise between you and the cylinder. I understand that they use centrifugal force to adjust the international space station; I can understand this working, as a space station has a certain amount of attraction to the Earth in other words sharing its gravity. If this was not true the space station would simply sit there while the Earth carries on its elliptical tour of the sun, and then eventually the Earth would catch up with it and collide. The only way I can see it working is, if the cylinder itself had a mass great enough for it to attract the mass of a person, it wouldn't have to be a huge amount but I don't think that would be feasible. There is no difference between the zero gravity on the outside of the cylinder and the inside of the cylinder. If you accelerate someone in space to say 10,000 miles an hour you would experience the force generated by the acceleration not gravity, as soon as the ship has reached its terminal velocity zero gravity does not simply return it was simple always there. As far as I can see generating gravity using Centripetal force is total science-fiction, am I wrong?