Random media variations focus waves into high-energy branches without any lens

Evidence

The focusing of the propagating wave in the rock below the surface is a sure-fire consequence of the variability of rock composition, density, and so on. It applies also to any waves propagating through random media: sound waves meeting pockets of warmer, cooler, or moving air; cosmic microwaves propagating through regions of outer space with interstellar dust; starlight propagating through the inhomogeneous atmosphere; electrons flowing though a semiconductor; or ocean waves propagating through current eddies. In all these cases and dozens more, the wave does not need a magical lens somewhere to focus the energy. Rather, small variations in wave speed from place to place deflect the rays seemingly randomly. If enough rays are traced out, it is found that they always focus down in groups to make hot spots and branches of higher wave amplitude, as seen in the Ripple simulation and ray tracing shown in figure 7. — Eric J. Heller, Why You Hear What You Hear- An…, 710

Categorization

• XREF: Connects to wave focusing phenomena across domains—cosmic microwaves, starlight, electrons in semiconductors—resonating with the reader’s interest in how environmental inhomogeneity shapes perception.
• DEFINE: Neither defines a term nor needs clarification; it states a general wave-propagation principle.