[ben_w]

> We can't fake gravity.

Yes we can, it’s a standard part of fairground rides.

(I’ll agree that the unknowns of space colonisation, and of the automation we’d need to be able to afford the infrastructure to even launch a serious effort, may prevent such colony efforts from happening)

[bena]

Centrifugal force does mimic gravity but it's not really something we can do at scale or even in space. When we're talking about a generation ship, we're talking about something a little larger than the Gravitron.

Not to mention, they work within Earth's gravity. Take a tube and spin it around you in space, it does nothing to you because there's no other forces working on you. Nothing putting you in the frame of the spinning tube.

Once you lose the Earth, it becomes a lot trickier to tie you to a frame of reference. Nothing we can make has the mass necessary.

The best we could likely do is accelerate a ship at 1G. But that has problems, because about halfway through your journey, you have to start decelerating. And there's also the issue of turning.

[ben_w]

> Take a tube and spin it around you in space, it does nothing to you because there's no other forces working on you.

Yes, it does — if you are in contact with the structure, the force you feel is the outside acting against your inertia to keep you in uniform circular motion. There is a layer of air in contact with the structure at any moment, so it ends up co-rotating, so anywhere inside except the axis of rotation itself will feel a force proportional to the distance from the axis.

> When we're talking about a generation ship, we're talking about something a little larger than the Gravitron.

Naturally. You can still spin them along and axis: https://en.m.wikipedia.org/wiki/O%27Neill_cylinder

We are a long way from been able to build such structures, and I have doubts about the suitability of human political psychology given the travel times involved and how long countries last for on average, but the physics of spin-gravity is fine, even though there may be noticeable Coriolis effects depending on scale.