"Solitude," wrote Henry David Thoreau in Walden, "is not measured by the miles of space that intervene between a man and his fellows. The really diligent student in one of the crowded hives of Cambridge College is as solitary as a dervish in the desert." If you're searching for solitude these days, even in Times Square, you won't need much diligence--just an iPod and a pair of earbuds. But watch out! Your solitude might be shattered by Tyler Cullen, a student filmmaker at the School of Visual Arts, who recently had the audacity to say to his fellow New Yorkers: Hey You! What Song Are You Listening To?