Ultra-high energy cosmic rays (UHECRs) are the most energetic particles observed in the Universe, with energies exceeding 10^20 eV, yet their origins remain mysterious. Lambda-CDM struggles to explain these particles because it requires extreme acceleration mechanisms and nearby extragalactic sources within the GZK horizon (roughly 50-200 Mpc), where CMB interactions would otherwise sap the energy of these particles during transit. The standard model lacks sufficient candidate sources with the requisite energy budgets and acceleration efficiencies, and the observed isotropy and composition of UHECRs are difficult to reconcile with expected galactic or nearby extragalactic source distributions (Alves Batista et al. 2019; Aab et al. 2020).