Duchamp looms large over debates about the role of the observer in art. Is the observer a passive non-participant willing to sit back and be entertained by the work, or is he or she an active partner in the experience? Naturally Duchamp would opt for the latter approach — even though it renders the artist less central to the process. And of course if both the artist and the observer are actively present, as Maria Abramovic is in her current MOMA show, then the encounter can become intense.