MOUNTAIN VIEW, Calif. — Google CEO Sundar Pichai broke a new barrier in artificial intelligence technology Tuesday when he unveiled a voice assistant that sounds exactly like a human voice.At the I/O developers conference, Pichai introduced Google Duplex, which allows the Assistant to speak with humanlike cadence and includes artificial intelligence that is able to comprehend context and unclear answers.Pichai demonstrated Duplex’s ability by having Assistant make reservations with a restaurant and a hair salon in two recorded phone calls.