U.S. copyright also has a constitutionally defined purpose: `[The Congress shall have Power . . . ] To promote the Progress of Science and useful Arts, by secu

U.S. copyright also has a constitutionally defined purpose: `[The Congress shall have Power . . . ] To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries.` Does the current scheme really promote the progress of science and useful arts? Is the current length of copyright really "limited Times"?