One key individual is crucial to saving the world from irrevocable destruction - possibly the universe (talk this over with editors and agents). Possibly, what with superstring theory and such, every available parallel universe - or most of them (what would be the effect on your writing style if you really had nine, or fifteen, or eighty-one dimensions to play with instead of a paltry three?) Let's say one of the available parallel universes, how many? nobody's really counted, survives - you'll admit the position of that one lone glimmering universe would be a perilous one. Let's not drop the ball guys, ok? But wait! by a time-paradox known only to our hero(ine) plus an intrepid team of supersmart confederates who may be killed off at will for the greater good of the story (after all they couldn't expect to outlive the universe anyway now could they? if they do nothing, or their plans fail, they'd only be advance scouts for the general catastrophe - that's good! work that into a nobly dying speech) where was I? Right, by a time-paradox known to the universe at large but generally scoffed at and disbelieved, it may be possible to pull all the lost universes back into existence through a strategically placed black hole, and then the onus isn't so much on the one universe left, illimitable though its inhabited worlds are. Of course there's a catch - ten black holes spaced about the galaxies seem likely candidates, but only one can be the right one, and the likely result of choosing wrong would be to implode, messily, the one universe we have left. There are tests that can be run, but the results they yield are only probable, with wide margins of error. One test would be irrefutably conclusive - unfortunately, in nine cases out of ten, no less than universally conclusive.
What to do? The universe is in no immediate danger that we're aware of, so perhaps best not upset the status quo ante. On the other hand, nobody expected the sudden annihilation of all the other universes either - wouldn't want to be caught napping twice or more accurately an infinite number of times, but most particularly not once more. Why keep all your eggs in one basket if you can fill it to the brim again? Wait a minute! by that analogy, is a universe an egg or a basket? Literally of course it's neither.
How many other universes are there anyway? None of our committee of thirteen has been to more than three besides our own, at least consciously. With overlaps, amongst ourselves, we could vouch for twenty nine or perhaps thirty. The Confederation President has visited six on frequent business, and had gone insane through sheer overload of mourning at the moment of near-universal catastrophe, having strong personal ties to each of them as well. I think that's the record though, and as for an exact count there's simply no counting.
How many times any of us have visited other universes unconsciously no one knows. How it's done of course is that you inhabit the parallel person (or place or thing, if it's a person-impoverished universe) whose role corresponds to yours in your universe of record. Sometimes people rapidly slip(ped) into and out of parallel universes in not too many blinks of an eye. In a universe very close to your own it might be possible to spend a day, or a week, without noticeable disorientation - though not without your place in ours being taken by the person you've displaced. Has this happened? Theoretically - up to a half year ago at least - it seemed inevitable, but there's never been any empirical proof, largely because it's hard to get any sort of a grip on what would constitute evidence of it happening. It's long been known however, that deja vu, presque vu and jamais vu are conditions associated with unconscious universe hopping. Jamais vu, the most extreme, is a result of finding yourself in a universe different enough that you're momentarily certain you've never been there before - which of course is true, but you wouldn't necessarily notice if the contrast with what you do know weren't so extreme.
When I say it's long been known about deja, presque and jamais vu, I mean of course that it's long been the subject of heated speculation and debate. It's only been known for certain in the last half year, since nobody's experienced any of those states since every universe but one vanished in a general catastrophe. We miss it, along with many other phenomena we hadn't realized were associated with a multiplicity (as opposed to a singularity) in the universe department.
Jamais vu of course isn't quite the most extreme reaction a universe hopper can be, especially when you consider how brief a visit jamais vu always entails. If the universe you're jumping from differs sufficiently from the one you land in, instant death or permanent madness is the result. Return seems impossible in such cases - certainly in every one we've been able to monitor.
We've had very little luck analysing the mad state of universe hoppers that have landed among us from elsewhere, simply because those we're able to study differ from us so profoundly in their initial make-up that it's impossible to determine what their mental state would be if we could restore it. Which is a pity, since it drastically limits our options in treating them - a few starved and a few others were poisoned while we determined by trial and error simply how to feed them - but we try to do our best, knowing we have hoppers of our own dependent on the kindness of races as supra-alien to us as we are to these. By now, of course, our hoppers have hopped into the void, and we'll have no more such shattered visitors - not unless we choose a black hole to shoot our time paradox through; and choose right.)
Uh-oh. I'm part of the Committee of Thirteen - don't even know how I arrived at that number. Better make sure I am the hero(ine) or at least a secondary principal who's indispensable to the sequel - second or third part of the trilogy I guess that would have to be. Don't see writing a credible follow-up to this, but why should I save uncountable universes in a one-off - surely that'll spin to three volumes, Lord of the Rings fat or thereabouts? Yeah - better hope I'm indispensable to plot development and action - don't want to go before my time, in my own book yet!
So: what to do? the universe will die sooner or later if we do nothing, but considerably sooner - is our best guess - if we do something and it's incorrect. "Incorrect is a considerable understatement. At least there'd be nobody alive to indict us for crimes against humanity." "Not to mention everything and everyone else." "That too." A couple of strong voices. Have to work on them a bit, come up with names eventually. They'd be on the side of scepticism and caution. They wouldn't be alone.
I wouldn't be with them though. I can already see myself insisting we proceed - after due deliberation (three volumes to fill) but with necessary haste (sooner or later it has to become a forced option and debate superfluous - need that for reader adrenalin) - roll the dice, finally, people: shoot that time-paradox off at whatever seems likeliest of the available holes. We have nothing to lose but everything, and a lot more everything to gain back if we succeed. Pascal would've taken the bet.