The Ladder Paradox

Simultaneity to the rescue

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• In the barn frame the contracted ladder fits; in the ladder’s frame the barn is even shorter.
• The resolution is simultaneity: the doors close at the same time only in the barn’s frame.
• Perfectly rigid objects can’t exist, since signals can’t travel faster than light.

Steps

1. Too long to fit?
2. The barn’s view
3. The runner’s view
4. Resolving it
5. Room to spare
6. A door that stays shut