What, if some day or night a demon were to steal after you into your loneliest loneliness and say to you: "This life as you now live it and have lived it, you will have to live once more and innumerable times more; and there will be nothing new in it, but every pain and every joy, and every thought and sigh and everything unutterably small or great in your life will have to return to you, all in the same succession and sequence? -- even this spider and this moonlight between the trees, and even this moment and I myself. The eternal hourglass of existence is turned upside down again and again, and you with it, a speck of dust!" Would you not throw yourself down and gnash your teeth and curse the demon who spoke thus? Or have you once experienced a tremendous moment when you would have answered him: "You are a god and never have I heard anything more divine." If this thought gained possession of you, it would change you as you are or perhaps crush you. The question in each and every thing, "Do you desire this once more and innumerable times more?" would lie upon your actions as the greatest weight. Or how well disposed would you have to become to yourself and to life to crave nothing more fervently than this ultimate eternal confirmation and seal? (Gay Science 341, Kaufmann trans.).
Unlike some readers of Nietzsche, I'm inclined to think Nietzsche intended his remarks about eternal recurrence not as a mere thought experiment but rather as a genuine cosmological possibility. His unpublished reflections on eternal recurrence suggest a view not unlike that of his contemporary, physicist Ludwig Boltzmann. In a universe of finite relevantly different combinatorial possibilities, infinite duration, and some means of avoiding permanent collapse into entropy, it is plausible to think that eventually the current configuration of the world will recur, not just once but infinitely often. And if one adds determinism to the picture (as most would have done in the 19th century), then once the current configuration recurs, the same subsequent states will follow. Voila, eternal recurrence.
Now update to the early 21st century by adding multiverse theory and randomness. What do we get? Eternal recurrence scrambled sideways! Sideways because the infinitely many duplicates of you need not exist only in your past and future (and in fact probably don't, assuming a finite or entropy-collapsing observable universe and universe-local spacetime) -- rather they exist "sideways", outside of our observable universe. And scrambled because rather than being destined always to play out the same, every finite possibility is played out, infinitely often.
So, on this view -- which is well within the range of the mainstream options in contemporary scientific cosmology -- there are infinitely many "Eric Schwitzgebel"s in infinitely many universes who have lived their lives identically to mine up to this minute. Given that there is a huge variety of highly improbable but finitely probable weird futures for these Eric Schwitzgebels, infinitely many Eric Schwitzgebels play out each of these weird outcomes. Infinitely many of my up-to-now counterparts decide to leave philosophy forever to pursue a hopeless career in football, infinitely many leap to death from the top of the tower, infinitely many spend the rest of the week stapling pages of Kant's first critique atop relevant passages of Hume's Treatise. And of course infinitely many also finish this blog post, in every possible way it might be finished.
How should I feel about these counterparts of mine, assuming such a cosmology is the correct one, as seems possible? They are oddly close to me, in a way, though universes distant. I can't quite find myself indifferent to them -- just as Nietzsche can't find himself indifferent to his future counterparts who must live out his every decision. Though it seems weird to say so, I find myself feeling sorry as I imagine their sufferings. I don't feel the heavy weight of Nietzsche's eternal recurrence, though. I'm not sure I would feel that weight even on Nietzsche's original assumptions, but definitely not now. Maybe instead there's a lightness: Even if I decide wrong, there will be infinitely many Erics who get it right! Conversely, there's an eeriness too: Infinitely many Erics bashed their cars headlong into that oncoming traffic.
Maybe I shouldn't take such reflections very seriously. The cosmology might not be correct. Even if it is correct, I'm the only Eric Schwitzgebel, UC Riverside philosopher, in this universe, and I really shouldn't care at all about what transpires in other universes, no matter how eerily similar. Should I? There are plenty of other people, right here on our own Earth, past and future, whom I should care about more, right? Because they're... well, why exactly? Because they're closer?