What's your question?

"Stand up if you have ever asked why. Why is the sky blue. Why do we have to. Why does that do that. Anybody. Stand up."

Say "stand up, or put a hand in the air if it's easier" — any child who uses a wheelchair or cannot stand easily takes part with a raised hand and puts it down on "sit down". The whole hall will stand. Let them look around before you carry on.

"Look at that. Every single one of you. Asking why is the entire job of a scientist — so you are all already doing it. Sit down."

"And here's the strange bit. When you're curious about something, your brain gives you the same chemical it gives you when you eat your favourite food. Being curious actually feels good."

Take a show of hands for each number first. Then press → to reveal.

"Three hundred questions, every single day, when you are four, five or six. The youngest children in here are the best question-askers in this building."

"By the time you're grown up, that drops to about twelve a day. Nobody makes them stop asking — they just quietly stop. Six weeks is long enough to make sure that never happens to you."

"'Why does the apple fall down, and not up?' Isaac Newton asked that. He found gravity."

"'If birds can fly, why can't we?' Two brothers asked that one. They built the first aeroplane."

"Marie Curie asked why some rocks glowed in the dark. She found two new elements — polonium and radium — used today in cancer treatment that saves millions of lives."

"Alexander Fleming asked why the germs weren't growing near a patch of mould. The answer was penicillin. Hands up if you think it has saved a thousand lives. (pause) A million. (pause) Two hundred million."

Count the room by eye. Don't tally. Then:

"Over two hundred million. From one question nobody else bothered to ask."

"Einstein asked what it would look like to ride on a beam of light. That question changed how we understand space and time."

"Stephen Hawking asked what happens at the edge of a black hole, and changed how the whole world understands black holes."

"Tim Berners-Lee asked what would happen if every computer in the world could share information instantly. He invented the World Wide Web."

"Turn to the person next to you. Tell them one thing you have wondered about. One sentence each. Go."

Ten seconds — no longer. Then cut it with your attention signal.

"Scientists make a bubble big enough to stand inside. Soap, water, a spoonful of cornflour, a little baking powder and a loop of string. That is the whole secret."

"This hall is hot. So — count with me. How long would a bubble last in here? One. Two. Three. Four. Five." (count out loud with them, slowly, and let the whole hall join in)

"this hall is hot, and that changes the answer. Hands up for five seconds. (pause) Hands up for fifteen. (pause) Hands up for thirty. (pause) Now stand up if you will commit to your answer in front of everybody. (let them stand — then tell them)"

"About five seconds in a room like this. In a cool, damp room — thirty. Same soap. Same bubble. Why?"

"The film. Soap makes two skins with a layer of water trapped between them. That sandwich is what holds a bubble together. Without soap, water just falls."

"The colours. Those swirling rainbows are called thin-film interference — the same physics as oil on a puddle, or the feathers on a magpie."

"The pop. A bubble pops when the water in the film dries out faster than gravity can drain it. Hot hall, five seconds. Cool and damp, thirty."

"And the trick the scientists use is a spoonful of cornflour and a little baking powder. Together they thicken the water so it drains out of the film more slowly. Without them, the bubble pops the moment it leaves the wand."

"A five-year-old can ask three questions about a bubble. What could you ask this afternoon?"

"Thumbs up if you learn better when you're interested. Thumbs down if you think it makes no difference. Keep them there and look at the screen."

"Scientists at the University of California gave one group of students facts they were curious about, and another group facts they found boring. The curious group remembered far more — and they also remembered random facts shown to them in between. Curiosity puts your whole brain on alert."

"So here's the trick. Pick something you think is boring. Ask one question about it. Then watch how much of it you remember."

Press → to reveal. Then ask the next two aloud — no slide needed:

"What holds a bubble together?" (soap — two skins with water trapped in between) · "How many whys a day this summer?" (one)

"Why does a bubble pop faster in a hot hall?" (the water in the film dries out faster than gravity can drain it) · "What did Tim Berners-Lee's question give us?" (the World Wide Web)

"You don't need a trip, or a garden, or a screen. Out of the window. In the queue. In your own kitchen. One why a day."

"And let yourself be surprised. Don't try to be too cool to say wow."

"Hands on your head if you'll do it. (pause — wait for the whole hall) Good. That's a promise. Off you go."

"stand up if you'll do it. Not for me — for you. (pause — wait for the last one up, and say nothing while you wait) Look at that. Every one of you standing has just promised it in front of the whole school. That's a promise. Off you go."