Quantum mechanics is a mathematical framework that describes the behavior of particles and systems at the microscopic level. In general, the equations of quantum mechanics are time reversible, meaning that they do not explicitly distinguish between the forward and backward direction of time.
The fundamental equations of quantum mechanics, such as the Schrödinger equation or the unitary evolution of a quantum state, are symmetric with respect to time. This implies that if you have the complete information about a quantum system at a particular time, you can theoretically use the equations of quantum mechanics to accurately predict its behavior both into the future and into the past.
However, it is important to note that the concept of time reversal in quantum mechanics is somewhat different from our everyday experience of time. In practice, certain processes in quantum mechanics are more likely to occur in one direction of time than in the opposite direction. This is because of a property known as "quantum decoherence," which refers to the loss of coherence and interference effects between different quantum states.
Quantum decoherence tends to cause irreversible behavior in many macroscopic systems and is responsible for the emergence of classical behavior from the underlying quantum world. As a result, while the fundamental equations of quantum mechanics are time reversible, the behavior of macroscopic systems that arise from these equations often appears irreversible in practice.
In summary, at the fundamental level, quantum mechanics is time reversible. However, due to the phenomenon of quantum decoherence and the emergence of classical behavior, the macroscopic world we observe often appears to be governed by irreversible processes.