De Broglie's 1924 heresy: everything has a wavelength, λ = h/mv. Electrons proved it within three years. Since then the experiment has been climbing the mass ladder: neutrons, whole atoms, a football of sixty carbon atoms and in 2019 a synthetic molecule of twenty-five thousand atomic mass units. The equations never flinch. What gives out is something else entirely.
Pick a projectile. The pattern is computed live by the same wavelet engine as chapter 2, at the true de Broglie wavelength, down to femtometres. Where no lab could see fringes, the engine still can; the readouts tell you who gives up first, and why it is never the mathematics.
Chapter 4's rule was that fringes survive only while no record of the path exists anywhere. A big, warm object cannot stop making records: it scatters gas molecules, and it glows. Every blackbody photon it emits is a little which-path detector broadcast into the room. Coherence decays as γ = e−N(πd/λenv)²: harmless while the environment's wavelength dwarfs the path separation, fatal the moment it doesn't. This is not a new law. It is chapter 4's γ, applied by the universe without asking.
Even the cricket ball has a wavelength, and the engine computes its fringe spacing without complaint. It is 10⁻³¹ m: twenty orders below a proton. No screen, no lab, no universe of patience could resolve it.
The absurd numbersIn 2004 Vienna heated C₇₀ molecules mid-flight. Above ~1500 K the fringes faded: each thermal photon carried away path information. Nobody was watching; the room was.
The heating experiment25,000 Da is a molecule of ~2000 atoms. Its de Broglie wavelength is 53 fm, five orders of magnitude smaller than the molecule itself. It still interfered.
Fein 2019, the numbers