Disclaimer: Science noob here, I may not use all terms correctly.
I've read somewhere of the following situation: An observer is inside a room (elevator) with no means of referencing anything outside. There is an apparent force that keeps everything stuck to the floor. 1) We can suppose that the room is standing on the surface of the Earth and objects inside are under the influence of gravity. 2) The room may be under uniform linear acceleration in the direction of the 'roof'. 3) The room may be swung around on a rope, with the floor opposite the direction of the centripetal force.
The observer inside the room can supposedly not determine which of the three situations pertain.
Question: Is this correct, and why?