Astrophysical collisions are central to the genesis of structure and life in the universe. Early on, particle collisions transformed the cosmic dark ages, big bang nucleosynthesis produced light nuclei while denser species grew through nuclear collisions in stellar cores. The aggregation of planetesimals also yielded planetary systems and conditions favorable to life. On larger scales, stellar mergers in binary systems, globular clusters, and galaxy centers are responsible for exotic objects such as kilonovae, black holes, and gravitational waves. High energy collisions occur in outflows produced by these exotic stellar objects, which could result in elusive neutrinos and ultra-high energy cosmic rays. Galaxy collisions can also dramatically alter the shape and state of all progenitors, while galaxy cluster collisions on even larger scales may inform us on the baffling nature of dark matter. The signatures and impact of astrophysical collisions prevail on all cosmic scales, yet the mechanisms for and outcomes of collisions in the Universe remain uncertain.

Some fundamental astrophysical questions include:

• What meteorites reveal about the early solar system?

• Can the outcome of planetary collisions be predicted accurately?

• How did heavy elements form in stellar collisions?

• What exotic objects do gravitational waves reveal?

• Do stellar collisions contribute significantly to the formation of massive stars or black holes?

• Which collisions produce the highest energy cosmic rays and neutrinos?

• How do collisions shape galaxy properties?

• Will Andromeda and the Milky Way ever merge?

• Can galaxy cluster collisions yield insights into dark matter interactions?

We are organizing a conference to review the state of the art in our understanding of the mechanisms and scales of collisions in the Universe. The connection between subfields of astrophysics will be emphasized. Major topics to be discussed at the conference include the physics of elastic and inelastic collisions in astrophysical contexts, predicting the outcome of small and large-scale astrophysical collisions, the production of the highest energy particles, modelling the sources of gravitational waves, observing and simulating galaxy mergers, constraining dark matter interactions, and more. These broad topics will appeal to all astrophysicists on a quest to constrain and master core processes in the growth of structure on all cosmic scales.