# What can pass through glass without breaking it?

Source: https://silverapuzzles.com/riddles/what-can-pass-through-glass-without-breaking-it

A physics riddle about a window. Something gets from one side of a pane to the other and leaves it whole.

**Answer:** Light.

Light shines through glass and leaves it whole.

Hint: Look at a window.

## How to think about it

1. Solid objects would shatter the glass, so the answer is not an object.
2. The hint says to look at a window. What comes in through a window all day without opening it?
3. Sunlight passes straight through clear glass; that is why windows are made of it.
4. Light goes through glass and leaves it unbroken.

## Why “Light” is the answer

Clear glass is transparent, which means light passes through it almost completely while the glass stays intact. That is the whole purpose of a window, and the riddle just asks you to name the thing a window lets in. Sound and heat also travel through glass to some degree, but light is the answer the hint points to.

## Common wrong answers

- **Sound.** Some sound does travel through glass, so it is a partial fit; the window hint points to light.
- **A bullet.** A bullet passes through glass by breaking it, which is exactly what the riddle forbids.