Already in classical physics, the definition of a "time-reversed" process is not obvious when the process is dissipative. In this talk, I shall explain how a general definition of such reverse processes can be obtained by appealing to logical inference. The reverse process is then seen as Bayesian retrodiction, implemented by the Petz recovery map in quantum theory. Most of the talk will be spent in introducing this new approach and its tools [1-2]. Specific research results obtained in the framework will be mentioned at the end [3-4].
 F. Buscemi, V. Scarani, PRE 103, 052111 (2021) https://arxiv.org/abs/2009.02849
 C.C. Aw, F. Buscemi, V. Scarani, AVS Quantum Sci. 3, 045601 (2021) https://arxiv.org/abs/2106.08589
 C.C. Aw, K. Onggandinata, D. Kaszlikowski, V. Scarani, PRX Quantum 4, 020352 (2023) https://arxiv.org/abs/2301.01952
 A.F. Ducuara et al., https://arxiv.org/abs/2306.00449
Valerio Scarani is Deputy Director of the Centre for Quantum Technologies, and Professor in the Department of Physics, National University of Singapore. He has contributed to the theory of quantum key distribution and Bell nonlocality (both foundational studies and device-independent certification). He has left these fields to evolve into quantum engineering, and is moving ahead to other fundamental topics -- possibly the focus of quantum engineering in a decade or so.