What is time? Is it a function of the expansion of space? Would it run backwards if space were contracting? If it did, what would that even mean if we were unable to stand outside of time and observe the difference? A musical composition is a four-dimensional sculpture in air (to paraphrase Frank Zappa), thousands of minutely crafted arrangements in sequence. It depends on the passing of time for its effect but, if well executed, should make us forget time is passing.