When Dudamel conducts an orchestra these days, he feels a ghost at his shoulder. The ghost belongs to his mentor, the Venezuelan conductor and educator José Antonio Abreu, who gave him both his musical training and his philosophy of life, and who had died just a few weeks earlier, in March, at age 78. “I lost Maestro physically,” Dudamel says, “but every time I do this” — he raises his hands as if he’s about to conduct — “a levare, to the orchestra, he’s there. He’s in the sound. I can hear him all of the time.”