What makes the past feel fixed in a quantum universe that never stops evolving? The Accessible Quantum Pastdevelops a rigorous answer: the past available to an observer is encoded in the physical records they can access—memories, detectors, and environmental traces—not in a mysterious destruction of the wavefunction. Using operator algebras and quantum-information theory, the work shows how accessible evidence accumulates, why recorded alternatives become increasingly distinguishable, and how the fidelity of those records sets quantitative limits on interference. It offers a new way to connect measurement, decoherence, quantum memory, and the emergence of classical facts while carefully separating established quantum mechanics from the additional assumptions that would be needed to make one experienced history fundamentally actual.