First a caveat, the following is largely the product of mine and one of my friend's late night discussions and so at best (I hope) will be a piece of entertaining philosophy, and at worst a load of dingo's kidneys. If you have the patience and forbearance gentle reader, then please read on and let me know your comments. 1
Towards the Multiverse
The many-worlds hypothesis states that at any one point in time the universe we live has one co-ordinate in a phase space, and it could be said that the laws of (quantum) physics determine the probability of going from this point to any other within this phase space. (That is to say; one arrangement of stuff going to a different arrangement of stuff)
Is there a level of complexity above this? Well if you consider that the phase space our universe has generated, its dimensionality will be determined by the amount of 'stuff' you started with, and any path through it describing its evolution
by the complexity of the laws of physics. It is each of these paths that we perceive as a coherent universe and the collection of paths through this phase space a 'multiverse'.
If there are no laws of physics then the stuff can't do anything, it'll just sit there. If there are too many laws then maybe the probability of going from one point in phase space to a wildly different point (meaning a radically different arrangement of matter, say a star jumping several light years or smearing itself out over an entire galaxy) will be so high, stable structures within that universe couldn't exist. Both of these extremes will have a lower volume phase space than the (multi) universe we see.
So making the following assumption :-
For each universe there will be a simplest set of physical laws, concepts if you prefer, that completely describe the behaviour of that universe.
Now you can imagine an abstract type of 'meta-phase space' with an infinity of dimensions, each co-ordinate describing a set of laws that gives rise to a different universe. Each one of these points can be 'unfolded' to reveal a further phase-space containing all the possible arrangements of stuff in the meta-phase space.
To describe a universe suffiecently complex to enable me to express these ideas, involves a whole set of fundamental physics, which can be expressed as mathmatical equations (but the term 'concepts' is as good as any I feel). The set of these rules must give a point in meta-phase space a certain distance from the zero co-ordinate. Around it in the same 'volume' you may well have other universes that wouldn't look too different from our own. However if you move too far in this conceptual meta-phase space (phase space where concepts are rearranged rather than matter), say making gravity ten times stronger, or it gets stronger over time, will soon have you in a completely unrecognisable place.
I have since learnt that super-string theorists talk of a 'string landscape'. Using the current way these theories are formulated, its possible to generate perhaps 10500 different types of universe.
Onwards and Upwards!
This begs the question : "If our universe can quantum tunnel from one point of its (material) phase space to another, can its laws also 'tunnel' from one point in this conceptual meta-phase space to another?" Well of course I don't know, but if it is possible then what that means is instantaneously the laws of physics would change over the entire universe. If the 'jump' was very small it's possible we wouldn't be able to perceive it without very careful measurements. Incidentally there's evidence that the fine-structure constant (which links many areas of physics together) may be changing; even the idea that the speed of light can change is being entertained, so this is not entirely without some grounding.
Maybe that in fact for a universe rich enough to maintain its complexity long enough to support an environment enabling me to be here (please see the anthropic principle) it is necessary for such a change in the laws of physics to be possible. If you liken the laws of physics to be a system of logic, and the stuff within it the symbols that are manipulated by it, then perhaps Godel's incompleteness theorem may hold. That means it might be possible for a universe to end up expressing a question that it finds impossible to answer. i.e. there's no way to decide what arrangement of matter comes next, which is another way of expressing the halting problem in computer/information science. By allowing the laws to change, you have a way out of this conundrum. Another way out might lie in the idea that its possible for one universe to bud off new universes, becoming a multiverse. For instance it's been suggested that when a star collapses into a black hole and down to a singularity at about the Planck volume a new universe could be formed. If this budding universe has a slightly different point in the conceptual phase space and it has at least some contact with the original, again you have a way out of the halting problem.
To Infinity And Beyond!
Allowing a universe to tunnel through the whole conceptual meta-phase space describing the multiverse of all possibilities implies there may be another level above this... A kind of metaphysics if you like, after all there should be rules that govern the wandering of a universe through this conceptual meta-phase space (or the propagation of a universe into a multiverse). I think I can just about picture this by thinking about our universe as its laws change, this would give our universe a trajectory through this conceptual meta-phase space. Allowing the metaphysics describing how likely it is to go from point to point to change, would cause this trajectory to suddenly look radically different.
So next in complexity above this is.....
There's a quiet fizzing noise, followed by a frisky sounding 'Pop!' as either CapnTrippy's head explodes, or the air rushes in to fill the vacuum left behind as he tunnels out of our universe...
Footnotes
1) Actually more of a disclaimer, firstly I'm not a physicist nor a philosopher, I merely have great fun thinking some thoughts as far as I'm able. The friend I first talked about this with was Warwick, a cruel thing to do as he'd recently been stabbed in the head with a fork. This is no joke.
2) More may follow here according to the feedback I get, and the time I have to pursue this and chase up some references for you to read.