Inverted world

Intuition tells us that a liquid will typically occupy the lower part of the vessel that contains it, and that buoyant objects will float on the upper free surface of that liquid. Benjamin Apffel and colleagues now turn this intuition on its head—literally. Vibration has previously been shown as a means to stabilize a denser fluid over a lighter one (even a gas phase), effectively ‘levitating’ the denser phase. But it now turns out that the buoyancy forces at the lower surface of such a levitated liquid phase act as if gravity itself has been inverted: bodies can float upside down on this interface, in a mirror image of what happens at the upper surface in the conventional non-vibrated case.