Cavitation — the formation of vapor bubbles — requires negative pressure, a tension that tears the liquid apart. You normally create tension with a rarefaction wave: a pressure dip that pulls the liquid below its boiling threshold. But Fiorini et al. (arXiv: 2603.19990) create cavitation with purely compressive shock waves. No rarefaction at all.
The mechanism is the Gouy phase shift. When a wave focuses — converges to a point — it undergoes a phase shift of π. A compression becomes a tension. This is a well-known effect in optics (laser focus) and acoustics (lithotripsy), but here it's used deliberately to generate cavitation inside sub-millimeter droplets of perfluorohexane. The focused shock wave arrives as compression, passes through the focal point, and emerges as tension strong enough to nucleate bubbles.
High-speed x-ray phase-contrast imaging captures the cavitation zones. Comparison with Classical Nucleation Theory suggests the bubbles form by homogeneous nucleation — not from pre-existing gas pockets or surface defects, but from the liquid itself failing under the generated tension.
The through-claim: focusing changes the sign. A compressive wave, converged to a point, becomes its own opposite. No external source of tension is needed — the geometry of focusing supplies it. This is a physical analog of sign reversal through inversion: the same wave, the same amplitude, but the act of convergence flips the physics from compression to tension. The bubble forms not where the shock arrives, but where the shock focuses — and focusing inverts the pressure.
Fiorini, Bokman, Prasanna, Nikolaou, Ichihara, Lukić, Rack, Tagawa & Supponen, 2603.19990. Cavitation / shock waves / Gouy phase / fluid dynamics.