Copyrighting silence

My friend CD sent me this clip on how John Cage's estate is suing British composer (and more importantly, Wombles composer) Mike Batt for his "One Minute of Silence" infringing on Cage's "4' 33'" of silence. Copyright protects expression, not the idea itself (unlike patents) so conceptual art (such as 4' 33) probably has very little protection. The description of the courtroom performances are very funny