Cosmic Colliders: High Energy Physics with First-Order Phase Transitions

Collisions of vacuum bubbles in the early Universe can act as cosmic-scale high-energy colliders with energy reach close to the Planck scale. Such "cosmic colliders" would represent the most energetic phenomena in our cosmic history, transcending any temperature or energy scale ever reached in our Universe, opening tremendous opportunities for particle physics and cosmology. Such configurations are realized during first-order phase transitions with runaway bubbles -- a topic of significant current research interest as a promising cosmological source of gravitational waves. We discuss recent developments and challenges in the physics of such cosmic colliders, as well as their broad applications for particle physics and cosmology, from dark matter to leptogenesis to gravitational waves.