A Morris–Thorne traversable-wormhole cross-section: the funnel shows the embedding profile r(l) = √(l²+r₀²) of the throat. Each dot is a photon fired along the axis with its own impact parameter b. Solve the null-geodesic radial equation (dl/dλ)² = 1 − b²/r(l)²: if b ≤ r₀ the light sails straight through the throat into the far side; if b > r₀ it hits a turning point where r(l)=b and bounces back — exactly like a particle reflecting off an effective potential.