All of monkeywicked's Comments + Replies

One thing about the MWI which confused me at first - The MWI is not a single interpretation, contrary to the name. There are several different versions of MWI floating around. I believe the original interpretation had the many worlds existing, but generally independent from one another; a single world represents multiple possible states, but as soon as a state is determined (whatever you want to call this process), the world becomes independent, and ceases to interact with the possible states which weren't realized in that world. (Although different books will tell you different things, this is, as far as I've been able to divine, the original one.) In the original version, worlds split, permanently, from one another. So there would be no way to communicate with them. I believe this is the version Yudkowsky follows. I've seen references to arguments that the fifth-dimensional variant (where worlds coexist and overlap, implying that some communication is possible) is impossible, but I've never seen the arguments themselves, in spite of looking.

I don't know of any models that propose a mechanism for such a communication (assuming you mean actually sending messages back and forth). A model like that would move the MWI from the realm of interpretations back into something testable. It would be way cool, of course, but don't hold your breath :)

Welcome to LessWrong! Here are some answers to your questions about MWI: 1. The space of possibilities in MWI is given by the configuration space of all the particles in the universe. The configuration space consists of every possible arrangement of those particles in physical space. So if a situation can be realized by rearranging the particles, then it is possible according to MWI. There is a slight caveat here, though. Strictly speaking, the only possibilities that are realized correspond to points in configuration space that are, at some point in time, assigned non-zero wavefunction amplitude. There is no requirement that, for an arbitrary initial condition and a finite period of time, every point in configuration space must have non-zero amplitude at some point during that period. Anyway, thinking in terms of worlds is actually a recipe for confusion when it comes to MWI, although at some level it may be unavoidable. The imporant thing to realize is that in MWI "worlds" aren't fundamental entities. The fundamental object is the wavefunction, and "worlds" are imprecise emergent patterns. Think of "worlds" in MWI the same way you think of "blobs" when you spill some ink. How much ink does there need to be in a particular region before you'd say there's a blob there? How do you count the number of blobs? These are all vague questions. 2. MWI does not play nicely with quantum field theory. The whole notion of a false vacuum tunneling into a true vacuum (which, I presume, is what you mean by vacuum decay) only makes sense in the context of QFT. The configuration space of MWI is constructed by considering all the arrangements of a fixed number of particles. So particle number is constant across all worlds and all times in configuration space. Unlike QFT, particles can't be created or destroyed. So the configuration space of a zero-particle world would be trivial, a single point. If you have more than one particle then all the worlds would have to have more than o

Yes; I like Steven Kaas's explanation: