Many possible worlds

Though it's easier to imagine possible worlds like parallel universes,
there's actually nothing 'parallel' about them - they are disconnected.

A ‘possibility’ is a way the world might have been. So for example, if I were to say that ‘flying pigs are possible’, this is to say that our world might have contained flying pigs, if it doesn’t already. There’s nothing contradictory about the idea of a flying pig; and furthermore, there is nothing in the laws of nature that rules out the existence of flying pigs. The reasons why we think flying pigs don’t exist is that we have never observed them; but this doesn’t affect whether or not flying pigs are possible. There could be some somewhere.

We are comfortable talking about possibility in every speech, but philosophers go one step further. For every logical possibility, there is a ‘possible world’ in which that possibility is said to take place. Thus, to say that ‘flying pigs are possible’ is to say that ‘there is a possible world in which there are flying pigs.’ If flying pigs were discovered to actually exist, then the possible world just described would turn out to be the actual world. It follows that there ‘exists‘ a possible world for every conceivable possibility - including worlds in which the laws of nature are different to the actual world. Let your imagination run wild with the possibilities - for every imaginable state of affairs, there is a possible world in which that state of affairs takes place.

It’s natural to think that possible worlds talk is just a useful way of conceptualizing possibilities. We normally assume that there exists only one world - the actual world in which we live. However, some philosophers (a minority) go even further - they hold that all the possible worlds exist just as much as the actual world. On this view, there really do exist worlds with flying pigs, mutant humans, and angry Greek gods. There also exist worlds in which you live, but have a different hairstyle. Or have fourteen fingers.

Our world is thus one world among many. We call it ‘the actual world’ because it’s the one we happen to inhabit. But when spoken by all the other people in the other worlds (including other versions of you), the phrase ‘the actual world’ refers to their world. There is thus nothing to really distinguish our world as ‘more real’ than the rest. Where are all these other worlds? Well, they’re causally and spatially disconnected from each other - and so it is not possible for us to access them.

Why think that there exist an infinite number of real, disconnected worlds? It helps solve lots of other tricky philosophical problems. (You’ll have to take my word for it). The question is whether this benefit is enough to convince us of their existence, and the reality of weird and wonderful things like flying pigs and fourteen-fingered humans, in the depths of logical space.

(Not to be confused with the ‘multiverse’ - a scientific hypothesis about many universes all existing in a single possible world - our world).