This preprint introduces the Unified Time Theory (UTT), a novel framework unifying General Relativity (GR), Quantum Mechanics (QM), Quantum Field Theory (QFT), and quantum gravity through a new time definition, tau, based on cosmic expansion and entropy. Developed by an independent researcher, UTT integrates Wheeler-DeWitt, Loop Quantum Gravity, and holographic entropy to address fundamental physics challenges. It resolves nine cosmological issues, including the Hubble tension (H_0 = 73.0 ± 0.5 km/s/Mpc), cosmological constant problem, CMB anomalies, flatness, baryon asymmetry, dark matter effects, strong CP problem, horizon problem, and inflation origin, while defining thermodynamic and cosmological time arrows. Validated against Planck 2018, SH0ES, and DESI data, UTT offers precise predictions testable by CMB-S4 and LISA, such as gravitational wave phase shifts (0.01 ± 0.002 rad). Numerically solved with high precision (error ~10^-8), this work proposes a transformative paradigm for theoretical physics, bridging macroscopic and quantum scales. Keywords: quantum gravity, cosmology, loop quantum gravity, Hubble tension, arrow of time, unification, general relativity, quantum mechanics, quantum field theory, holographic entropy, cosmological constant, dark matter, strong CP problem, inflation. Keywords: quantum gravity, cosmology, loop quantum gravity, Hubble tension, arrow of time, unification, general relativity, quantum mechanics, quantum field theory, holographic entropy, cosmological constant, dark matter, strong CP problem, inflation