In 1957, while on a family vacation, Bill Viola fell into a lake. He was six years old. Sixty years later, Viola, who has died at age 73, recalled the event. "I wasn't holding on to my float when I got in the water, and I went all the way to the bottom," he said. "I had this weightlessness and a profound visual sensation that I've never forgotten. It was like a dream and blue and light, and I thought I was in heaven because it was the most beautiful thing I'd ever seen." And then ... "my uncle pulled ...