Reddit mentions of Thus Spoke Zarathustra: A Book for Everyone and Nobody (Oxford World's Classics)

First thing's first, get yourself a better translation. I know the Common translation is free online, but it's an outdated translation with it's own issues, and you'll understand the text better in a more contemporary translation anyways. I like this translation personally because it has great footnotes, but the Cambridge has become the standard, and it's not a bad translation either.

Okay. So let's work through your questions sequentially.

1. The Big Bang theory as we know it was not formulated until the early 1900's, and even then it was in it's nascent stages as a theory and would be almost unrecognizable to us in the way that the layman understands it. So, it's probably safe to say that Nietzsche isn't concerned with TBBT.
   
   That said, I think it's a mistake to read this particular passage as an instance of a metaphysical claim. Zarathustra is talking about a vision that he had, and after all, he is a prophetic character. So it's probably best to look past the metaphysical propositions and just assume that time functions in this fashion, what does that say?
   
   
2. My response picks up here. One's life, according to the Eternal Recurrence, occurs again and again, the same way, ad infinitum. Zarathustra, as an individual in the moment (hence moment is inscribed on the gateway overhead), only has the perspective in the present moment, yet he can see that life goes on infinitely forwards and infinitely backwards. They aren't two separate entities which flow into one another, it is all one constant "line", if you will, which flows infinitely in one direction. Zarathustra, in the present moment, exists on a single point on that continuum.
   
   I wouldn't make heavy weather of the word antithetical. Perhaps the better translation will help.
   
   > They contradict each other, these paths; they blatantly offend each other - and here at this gateway is where they come together.
   
   
3. The dwarf is not echoing Zarathustra. The del Caro translation:
   
   > 'All that is straight lies,' murmured the dward contemptuously. 'All truth is crooked, time itself is a circle.' 'You spirit of gravity!' I said, angrily. 'Do not make it too easy on yourself! Or I shall leave you crouching here where you crouch, lamefoot - and I bore you this high!
   
   The dwarf is speaking platitudes. It's easy to say that time is circular and that you're just coming back to the same moment, doing the same thing, over and over again, returning endlessly to this same spot, but one almost gets the sense that the dwarf is speaking about metaphysical truths, or perhaps trying to make this metaphysics instead of what it really is, the wonderful affirmative thing that follows (the vision of the shepherd).
   
   The spirit of gravity is the spirit of seriousness, something which Zarathustra detests. He's not talking about physics, and he's not referencing any metaphysical theories, so don't worry about dimensionality or gravity as a force, or anything like that.
   
   And yes, he retains a linear concept, but only to preserve the metaphor of a "path" upon which one walks. Hence earlier he says "Two paths come together here; no one has yet walked them to the end". Don't think that there is a physical end or that it's talking about physics. Just focus on the fact that it's your path, one which stretches infinitely.
   
   
4. From my translation:
   
   > And are not all things firmly knotted together in such a way that this moment draws after it all things to come? Therefore - itself as well?
   
   Essentially, all of time sinks into the present moment. You're never outside of the present moment, and so the moment draws all things in, including itself, in the sense that the moment which you conceive of as the present is already past, and so it must continually draw all of time into the present moment going forward into the future.
   
   Okay, so the point is that this book, and this passage, and this teaching are fundamentally existential, which is to say that they speak to one's existence. One must live in the present moment, one must always and eternally experience the present moment the same way, and one must always walk the same path. Yet this path is not numerically the same, it's different every time.
   
   I think Deleuze points out somewhere (probably in his book on Nietzsche), that this particular part of the vision is an awful one, about shallow metaphysical propositions, and thus one might call it The Eternal Return (because everything returns to the moment, like a baseball falling back down after it's been tossed), whereas the Eternal Recurrence, probably represented by the shepherd in the next part, is life affirming and transformative.
   
   I hope that helps a little. It might behoove you to separate yourself from concerns about physics, given that it's not really a common reading of the work, nor is it a defensible one unless you do a ton of work, and even then it's not entirely convincing. It's a way of reading it, but I don't read it that way.