A world with a vast inner space, entered through the poles? Seismographs settle it. When a big quake hits, stations on the far side sit in a P-wave SHADOW ZONE (about 103° to 142° away) — a ring of silence that only exists because a dense, LIQUID outer core bends and blocks the waves. A hollow planet would ring like a bell instead. Slide the source and watch the shadow fall. Verdict: DEBUNKED.
Direct P-waves from a quake are refracted sharply at the core–mantle boundary and absent between ~103° and ~142° of angular distance — the P-wave SHADOW ZONE. Its geometry requires a dense core whose outer part is LIQUID (S-waves, which can’t cross liquid, vanish entirely beyond ~103°), and later PKIKP arrivals reveal a SOLID inner core. This is how we know Earth’s interior is full and layered, not hollow. A fail-loud self-check throws unless the shadow spans >30° starting past 100°. ◆ VERDICT: DEBUNKED — seismology maps a solid/liquid interior directly.
The 103°/142° bounds are standard textbook values (a few degrees vary with model); the inference chain (shadow → liquid outer core; S-wave loss → no through-liquid; PKIKP → solid inner core) is settled geophysics.