In Gamow's short book 'Gravity' he describes the effect of lunar gravity on the earth, in particular the seeming paradox that the oceans, in response to the tug of the moon, swell both in the direction of the moon and on the opposite side as well. He resolves the paradox by explaining that Kepler's laws require that the greater angular velocity of water on the opposite side of the earth send them further out, to satisfy the requirement that greater velocity implies a greater distance from the orbital focus. My question is this: where does the extra water come from? Is water from the poles drawn down to form the tidal surplus? There is no net addition of water, and water does not "expand." Does this mean that sea level at the poles drops? Thanks for any enlightenment.