If we live in a multiverse and not a universe, then what we’ve long believed to be true is not true. Or at the very least, it’s a small sliver of the truth. From an excellent Aeon article on the topic by Michael Hanlon: 

“The new terrain is so strange that it might be beyond human understanding.

That hasn’t stopped some bold thinkers from trying, of course. One such is Brian Greene, professor of physics and mathematics at Columbia University in New York. He turned his gaze upon the multiverse in his latest book, The Hidden Reality (2011). According to Greene, it now comes in no fewer than nine ‘flavours’, which, he says, can ‘all work together’.

The simplest version he calls the ‘quilted multiverse’. This arises from the observation that the matter and energy we can see through our most powerful telescopes have a certain density. In fact, they are just dense enough to permit a gravitationally ‘flat’ universe that extends forever, rather than looping back on itself. We know that a repulsive field pervaded spacetime just after the Big Bang: it was what caused everything to fly apart in the way that it did. If that field was large enough, we must conclude that infinite space contains infinite repetitions of the ‘Hubble volume’, the volume of space, matter and energy that is observable from Earth.

If this is correct, there might — indeed, there must — be innumerable dollops of interesting spacetime beyond our observable horizon. There will be enough of these patchwork, or ‘pocket’, universes for every single arrangement of fundamental particles to occur, not just once but an infinite number of times. It is sometimes said that, given a typewriter and enough time, a monkey will eventually come up with Hamlet. Similarly, with a fixed basic repertoire of elementary particles and an infinity of pocket universes, you will come up with everything.

In such a case, we would expect some of these patchwork universes to be identical to this one. There is another you, sitting on an identical Earth, about 10 to the power of 10 to the power of 120 light years away. Other pocket universes will contain entities of almost limitless power and intelligence. If it is allowed by the basic physical laws (which, in this scenario, will be constant across all universes), it must happen. Thus there are unicorns, and thus there are godlike beings. Thus there is a place where your evil twin lives. In an interview I asked Greene if this means there are Narnias out there, Star Trek universes, places where Elvis got a personal trainer and lived to his 90s (as has been suggested by Michio Kaku, a professor of theoretical physics at the City University of New York). Places where every conscious being is in perpetual torment. Heavens and hells. Yes, it does, it seems. And does he find this troubling? ‘Not at all,’ he replied. ‘Exciting. Well, that’s what I say in this universe, at least.’”

••••••••••

Brian fails to complete his novel in several universes: