These are the albums that made the Universe... if you are new to Ayreon, it is highly recommended to start with these in this particular order!
With the release of the 01011001 studio album and Timeline compilation album Arjen finally considered the events of Ayreon Universe closed. Fortunately later he changed his mind and returned to the Project. The Theory Of Everything does not really fit to the classic storyline, but with The Source Arjen created a sequel to 01011001. However there is no such official borderline, (for me at least) these new albums represent a new age of Ayreon... both albums have undeniably different musical and lyrics style, a bit more conversational, a bit more... but experience it yourself!