What Happens If a Glass of Water Is Literally Made Half Empty by Vacuum Pressure

As part of their ongoing “What If?” series, Randall Munroe of xkcd and Henry Reich of MinutePhysics explain what would happen if a glass was literally made half empty due to vacuum pressure.

But what if the empty half of the glass were actually empty. A vacuum. The vacuum would definitely not last long. But exactly what happens depends on a key question that nobody usually bothers to ask: Which half is empty?

The experiment included all possible answers to the question.

For our scenario, we’ll imagine three different half-empty glasses: the traditional air/water glass, a vacuum-on-top glass, and a vacuum-on-bottom glass. We’ll imagine the vacuums appear at time t equals 0.

In all cases, the glasses shattered. But even in this a good lesson was learned.

The lesson: If the optimist  says the glass is half full, and the pessimist says the glass is half empty, the physicist ducks.