The Literal Half-Empty Glass

In this episode of of the What If? series (previously at Neatorama), we get classically literal. The old saying is that an optimist looks at a glass of water and sees it as half-full, while a pessimist looks and sees the same glass as half-empty. Meanwhile, a pedant looks at the same glass and says that it contains a combination of 50% drinkable liquid and 50% air. That's pretty much when a logical discussion shuts down and people try to change the subject. We all know what an empty glass means; we've washed a lot of them. But if you are going to get really literal, you can forget all about optimists and pessimists. What does a physicist (Henry Reich) and an engineer (Randall Munroe) make of a glass that is only 50% full, and the rest is ...nothing? That means a vacuum, and a glass in that situation can get violent. Strangely, the effect can be recreated in real life, but be sure to have a broom and some paper towels handy.