But bits are abstractions encoded in the physical world which is not at all 'either there or not' anywhere near the scale of writable CDs. For starters for every 24 bits of data 56 bits are written on the physical media (8 to 14 encoding and a redundancy byte for every 3 data byes) and then the pits and lands are written into dye ... much like a written page if you language consisted of a very long straight series of lines of varying length.