Ai Weiwei's new exhibition at Alcatraz, a first for the site, and in spite of his not being permitted to leave Beijing."It’s as if, in the years since his detention, Ai has given up on metaphor. He sees art less as a means of self-expression and more as a global lingua franca. Contemporary art, in his view, requires and perhaps even creates an audience committed to liberty. Presenting his art in a prison amplifies that goal twice over. ...Not all of Ai’s heroes are reachable, of course; Liu Xiaobo, Nobel Prize be damned, is still incommunicado in a prison in Liaoning."