Finnegans Wake: The Title

Finnegans Wake The Title“Hovering over the title of Joyce’s neologistic book, the apostrophe exists in relation to it rather as a quark fired at a double slit might relate to the rest of the world : it would be simultaneously here, there and not-there, working its magic in a wholly ghost-like fashion.”What does an apostrophe usually indicate?Adding an apostrophe to ‘Finnegans’ should change its meaning. What other meaning (or meanings) are available? Why the ambiguity?