If the earth was flat, and there were no such thing as gravity, and it, along with all the celestial bodies, accelerated upwards (so, parallel to normal) at 1g(9.8m/s^2), what would happen if I dropped a pen while I am on earth?
Yeah, but one doesn't need to do that on a "flat" earth! An ordinary earth that we have right now is pretty sufficient, don't you think?So harsh guys! This is the legitimate basis of general relativity. It would be very difficult to distinguish this kind of acceleration from "gravity" (you'd need to compare measurements from separated places, much as were used the first time to show we don't live in a discworld).