Master ONE relationship — the Compton shift: Δλ = 2.43 (1 − cos θ) pm, λ′ = λ + Δλ Forward, inverse (solve for θ), and backward (recover λ) on an unknown source.
⚠️ Misconception to break
"Waves can\u2019t push, and scattered light keeps its wavelength." Classical physics agreed — and was wrong. The photon recoils off an electron like a billiard ball, paying momentum and leaving longer.
🧪 Model & assumptions (stated honestly)
Free, initially-at-rest electron · teaching value λc ≈ 2.43 pm (exact 2.4263) · wavelengths drawn ~10¹¹× larger for viewing (real: picometres) · the electron\u2019s recoil direction is illustrative — its exact formula is another law and stays out of this game · angles are exact.
1️⃣ Billiard Room · Watch — the shift ignores the incoming λ 2️⃣ Cross-Examination · Predict — Δλ and λ′ arm the shot 3️⃣ The Angle Cut · Inverse — the window wants λ′; you aim θ 4️⃣ The Verdict · Crisis — unknown source, 90 s, judgement Bronze+ seals the next exhibit. Scenarios re-roll every retry.
Controls
Space fire · Enter commit · P pause · R reset exhibit · H hint. Each exhibit opens with a 🧠 reasoning question. Wrong submissions −2 pts.
🏅 How scoring works
Every stage: answer the reasoning question, then compute and commit a number. Your medal is set by accuracy — 🥇 under 5% · 🥈 under 10% · 🥉 under 20% error — and a Bronze or better unlocks the next stage. A wrong answer costs −2 points (−1 on Easy, and your first reasoning slip on each question is free on Easy). A hint costs −3/−4/−5. Fewer tries and higher accuracy mean a higher score — so it always pays to calculate, not guess.