My sleepy contribution for tonight's lightspeed episode before I retire, will be some tidbits on our glimpses of Dan's notebook. Here is a link for a good start in deciphering what he's got scribbled in his pages, such as lightcones tipping, Eddington-Finkelstein, etc:
It all has to do with black holes, event horizons, and the photons in lightcones escaping (or not) from said event horizons. Whew. Are TPTB really going to show the island going through a black hole? If so, I can't wait...but I thought they said there would be no black holes, way back when. Anyway, if you have the stomach for it, keep clicking on "Go to next section" on the bottom left of each page in the link above, for more space-time fun! I found this illustration interesting, because it mentions "time reversed". And when Locke flips that switch in the Orchid, I hope that we hear some major sound effects, like how the TARDIS sort of gasps it's way through time...and more purple skies too.
2costa over at TLC made note of this Wiki page which does show many similarities to Dan's formulas, and also defines the variables used (I know, not exactly light reading here in this post, but it's kinda fun):