Deep leing is driving a radical paradigm shift in wireless communications, all the way from the application layer down to the physical layer. Despite this, there is an ongoing debate as to what additional values artificial intelligence (or machine leing) could bring to us, particularly on the physical layer design; and what penalties there may have? These ques-tions motivate a fundamental rethinking of the wireless modem design in the artificial intelli-gence era. Through several physical-layer case studies, we argue for a significant role that ma-chine leing could play, for instance in parallel error-control coding and decoding, channel equalization, interference cancellation, as well as multiuser and multiantenna detection. In addition, we discuss the fundamental bottlenecks of machine leing as well as their poten-tial solutions in this paper.