Antibubbles

A regular soap bubble is a thin film of liquid surrounding a sphere of air and floating in an air medium.

Now think of the exact inverse: a thin film of air surrounding a sphere of liquid and floating in a liquid medium. That is called an antibubble. You can make them in a beaker of soap bubble solution.

An antibubble, with its modest bouyancy, floats slowly upward to the surface just as a soap bubble floats delicately downward.

This YouTube video has other permutations: zero gravity bubbles, bubbles-within-droplets, and a "bubble war" filmed in slow motion and explained by a NASA scientist.



Wikipedia on Antibubbles, link.