I just heard something that made me realize I was taking the equivalence principle way too literally. If I were in a windowless room, and was standing on its floor, then there is, in principle, a performable experiment by which I could determine whether I was moving upward at 1 g of acceleration, or whether I was standing on a massive body generating 1 g of gravity. I always thought such an experiment was impossible, but gravity causes tidal forces while acceleration doesn't. Or does it? Are they equivalent or not?