Schrodinger's Catch - Portal 2

Catch a blue-painted box before it touches the ground - 20

In Chapter 6, there is a test chamber using Repulsion Gel. You have to portal the Repulsion Gel into the glass box, from above. The cube will before covered in the gel and bounce uncontrollably across the test chamber. I recommend saving before you portal in the Repulsion Gel. If you drop it, restart and hope it bounces towards you.

This achievement is a reference to Schrodinger's Cat. I paradox devised by Erwin Schrodinger, explaining how an object can be in two different states at the same time, you cannot know what state it is until you have seen it. So a cat is trapped in a box, with a radioactive source - the cat can be dead and alive at the same time because you cannot see the cat's state until you open the box.

Schrodinger's Cat