The gravity idea for a flat earth would be impossible, as you would have to constantly be accelerating, which according to quantum physics is impossible, but you probably think thats a conspiracy as well right?
The whole concept of a flat earth is flawed in so many ways, at least RE'rs have some kind of proof, pictures etc. even if you think their photoshopped (yeah Photoshop 1958). You have no evidence of the world being flat, any pictures to beyond any shadow of a doubt that the earth is flat.... NO, for a round earth (well technically its not a sphere its more elliptical than anything), YES we do....
Disclaimer: (I suppoert RET and Gravity... but will play devils' advocate with this statement)Actually... you need to go back and brush up on your Einstein a bit more.
Although it is true that you cannot sustain a true accelleration of 9.81 meters per second squared indeffinitely, the fact is, is that you can indeffinitely sustain your perception of an accelleration of 9.81 meters per second squared in your particular velocity frame of reference.
According to Einstein, as you approach the speed of light, your perception of space and time warps such that although from an outside stationary point it would appear that you rate of acceleration is deteriorating to the ultimate and unachievable point that is the speed of light in a vaccuum, your perception of forward accelleration will remain unchanged in your own frame of reference and you will still continue to experience a force as if it were 9.81 meters per second squared accelleration.