Mystery #4Tier 1-2sound / waves
Why do you hear an echo?
Shout "hello!" into a valley or a big empty hall, and a moment later the valley shouts "hello!" right back at you, in your own voice. Nobody is there. Where does that delayed copy of your voice come from, and why does it always arrive a beat too late?
Your guess
What's your hunch about what makes your voice come back to you as an echo?
There's no single magic word to type, have a go in your own words, then reveal the answer to see how close you got.
Make a guess to unlock the hints and the answer.