Cost: $15–20, single Walmart/Kroger trip Time: 30 min setup, 10 min wait, then it runs for ~1 hour Difficulty: ★☆☆☆☆ (no electronics, no soldering, no programming) What you get: White streaks crossing your tank every minute or so. Each is a cosmic muon that should not exist by its naked lifetime — it only made the trip to your kitchen because time slowed for it by ~40×.
| Item | Where | Price |
|---|---|---|
| Clear plastic container, ~15×15 cm, ~5 cm deep (Tupperware, Snapware, fish-tank lid, glass bake dish) | kitchen aisle | $3–5 (you may have one) |
| 99% isopropyl alcohol, 16 oz bottle | pharmacy aisle | ~$5 |
| Black felt or thick black cloth, ~30×30 cm strip | crafts aisle or scrap | ~$3 |
| Aluminum baking sheet or pie tin | kitchen aisle | ~$3 (you may have one) |
| Strong flashlight | hardware aisle (you have one) | $0 |
| Dry ice, ~2–3 kg | gas station, Kroger, Publix, Walmart freezer; CALL AHEAD | $10–15 |
| Thick gloves (oven mitts work) | (you have these) | $0 |
| Black permanent marker (Sharpie) | school supplies | ~$2 |
| TOTAL | $15–25 |
Dry ice: not every store carries it. Call ahead. In US: Kroger / Publix / Safeway usually do. Some Walmarts do. Also try a local welding/gas supply company (cheaper, ~$1–2 per pound, but you need to bring a cooler).
Easier alternative geometry: don’t invert. Use the container right-side-up with the alcohol felt taped to the lid, then sit the container on top of the dry ice on the baking sheet. The dry ice cools the bottom of the container, the felt at the top releases vapor downward, and the cold bottom creates the supersaturated layer. CERN’s S’Cool LAB has photos: https://scoollab.web.cern.ch/cloud-chamber
| Track type | Source | Look |
|---|---|---|
| Muon (your target) | Cosmic ray, ~75% of ground radiation | Long, very straight, full chamber crossings |
| Alpha | Radon decay (background in any room) | Short, thick, intense |
| Electron / beta | Beta decay or cosmic electron | Wiggly, often curved |
| Cosmic shower | High-energy primary fragmenting in atmosphere | Multiple tracks from one point |
Rate at sea level: roughly 1 muon visible per minute in a 15×15 cm chamber. Less if you’re indoors with concrete shielding above, more at altitude or near a window.
The straight tracks crossing your chamber are muons created ~15 km above your house when cosmic ray protons hit the atmosphere. A muon’s proper lifetime is 2.197 µs (PDG 2024 measurement, accurate to parts per million).
If muons didn’t experience time dilation, at v ≈ 0.998c they’d travel 0.998 × 3×10⁸ × 2.197×10⁻⁶ = 658 m before decay. They’d never reach you. Almost zero should hit the ground.
But they do — by the hundreds per square meter per second.
The reason: from your frame, a 4 GeV muon (typical) has Lorentz factor γ = E/mc² = 4000/105.7 ≈ 38. Its lifetime in your frame is 38 × 2.197 = 83 µs. Distance traveled: 0.998c × 83 µs = 25 km, easily making the 15 km trip.
So when you see a straight white streak in your tank, you are seeing a particle that has time-dilated by γ ≈ 40 to reach you. The cloud chamber is the cheapest, most viscerally direct time-dilation experiment one human can do in their kitchen.