Special relativity predicts distortions in time and space. Image by bluebudgie from Pixabay

The Ladder Paradox Resolved

A thought experiment in special relativity

The ladder paradox — also known as the barn-pole paradox — is a thought experiment in special relativity. At first, the scenario appears to produce conflicting results. A closer examination helps us to resolve the apparent paradox.

(New to special relativity? Perhaps read these first:

• The Andromeda Paradox Explained
• The Twin Paradox Explained
• The Unattainable Speed of Light)

Here’s how it works.

The setup

Bob and Alice are planning to elope. Bob will provide the ladder and Alice will provide the 2nd-storey window. A problem is the barn between the road and Alice’s window. Bob must carry the ladder through the barn. The ladder is much longer than the barn. The barn has a front door and a back door. The catch is this: only one door can be open at any moment.

How will Bob get the ladder through the barn?

Fig. 1: How can Bob fit the ladder in the barn?

Alice presents a brilliant solution. She knows that according to special relativity, if Bob picks up enough speed, the ladder…