One of the most successful props I have used at outreach events is the “Build Your Own Universe” Lego kits produced by QMUL. These are incredibly simple—the kit just consists of a bag of red and yellow Lego bricks. But this is all you need to explain primordial and stellar nucleosynthesis—that is, how the atoms in the Universe were forged in the conditions after the Big Bang, and in the heart of stars—to young children.
The lesson begins at the start of creation. The Big Bang produced enormous numbers of building blocks, including up quarks (the yellow bricks), and down quarks (the red bricks).
A fraction of a second later, the Universe became cooler, and the quarks stuck together to form protons and neutrons. Snap together two yellows and a red to make a proton, and two reds and a yellow to form a neutron.
Three minutes later, the Universe had further cooled so the protons and neutrons could stick together to make nuclei. Stick your neutron onto your proton and you have made the lightest nucleus, deuterium. Add another proton and it turns into helium-3. The next-heaviest nucleus is helium-4, made from two protons and two neutrons. Get some more bricks, snap together two yellow-yellow-red and red-red-yellow combos and fix them into a ring.
For a long time, all the nuclear matter in the Universe consisted of a few light elements—hydrogen and helium (and a bit of lithium). After 379,000 years it was cold enough for electrons to stick to these nuclei, creating the first atoms. (Electrons can be represented by little white bricks if you like). Then after 100 million years things got more interesting. The gas clouds collapsed under their own gravity and became hot and dense enough to ignite nuclear fusion. The first stars lit up the Universe as they fused hydrogen nuclei into helium, and helium into heavier elements including oxygen, nitrogen and carbon, the building blocks of living cells. Once their hydrogen supply was exhausted, the heaviest stars fused more and more elements, and finally exploded in a supernova with such energy to produce the heaviest nuclei. This way all the elements in the Periodic Table were created.
Any child getting this far deserves a ‘I’m made of stardust’ sticker.
This kit was developed by Ben Still at Queen Mary, University of London. I note he has a book coming out in September on Particle Physics Brick by Brick. I will certainly be getting a copy.