Reasoning:
- If our vacuum is metastable, its lifetime already exceeds the universe’s age (we exist); the only collider-specific worry is collision-stimulated nucleation.
- Nucleation probability per collision can only depend on the collision’s CM energy and local conditions, both matched or exceeded by cosmic-ray collisions ~1e31 times over (Kobzarev-Okun-Voloshin; Hut-Rees lineage, refs [7]).
- A bubble, once nucleated, expands at essentially the speed of light in every frame — a light-cone phenomenon, not a massive particle that must stop somewhere. So the boost disanalogy between collider and cosmic-ray production is irrelevant here: this is the cleanest application of the cosmic-ray bound, and the 2008 report simply reiterates that nothing since 2003 questions it.
Validity verdict (step 6)
Reconstruction: premises = nucleation probability per collision depends only on CM energy and local conditions (matched ~1e31 times by cosmic rays), and a nucleated bubble expands at essentially light speed. Load-bearing step traced: bubble growth is a light-cone phenomenon, not a massive product that must stop, so production-frame boost is irrelevant and the slow-vs-fast loophole genuinely does not apply - this is the cleanest application of the cosmic-ray bound. Undercutting probe: could collider conditions differ in some nucleation-relevant way other than CM energy (density, repetition)? Cosmic-ray collisions on nuclei match or exceed these too; conditional on the premises no defeater survives.