Concept behind levitating object mirage

[Numzie]

I'm sure you've hear or seen this. Its a device that has two bowl shaped mirrors on top of each other, facing each other and the top bowl has a hole cut in the top. The device creates a mirage of any object placed at the bottom that seems to levitate above the hole. How can this phenomena be explained and what concepts are used to create the illusion?

 

[Doc Al]

Check out this thread, especially the video link in post #2: https://www.physicsforums.com/showthread.php?t=187709

Here's another thread in which I give a brief explanation: https://www.physicsforums.com/showthread.php?t=74837