Windows on the Universe: Establishing the Infrastructure for a Collaborative Multi-messenger Ecosystem

In this White Paper, we present recommendations for the scientific communityand funding agencies to foster the infrastructure for a collaborativemulti-messenger and time-domain astronomy (MMA/TDA) ecosystem. MMA/TDA ispoised for breakthrough discoveries in the coming decade. In much the same waythat expanding beyond the optical bandpass revealed entirely new and unexpecteddiscoveries, cosmic messengers beyond light (i.e., gravitational waves,neutrinos, and cosmic rays) open entirely new windows to answer some of themost fundamental questions in (astro)physics: heavy element synthesis, equationof state of dense matter, particle acceleration, etc. This field wasprioritized as a frontier scientific pursuit in the 2020 Decadal Survey onAstronomy and Astrophysics via its "New Windows on the Dynamic Universe" theme.MMA/TDA science presents technical challenges distinct from those experiencedin other disciplines. Successful observations require coordination acrossmyriad boundaries -- different cosmic messengers, ground vs. space,international borders, etc. -- all for sources that may not be well localized,and whose brightness may be changing rapidly with time. Add that all of thiswork is undertaken by real human beings, with distinct backgrounds,experiences, cultures, and expectations, that often conflict. To address thesechallenges and help MMA/TDA realize its full scientific potential in the comingdecade (and beyond), the second in a series of community workshops sponsored bythe U.S. National Science Foundation (NSF) and NASA titled "Windows on theUniverse: Establishing the Infrastructure for a Collaborative Multi-MessengerEcosystem" was held on October 16-18, 2023 in Tucson, AZ. Here we present theprimary recommendations from this workshop focused on three key topics --hardware, software, and people and policy. [abridged]