According to the standard model, the limit of nature is a cosmic singularity, and the limit of causality is whatever generated and sustains this singularity (standard cosmology merely purports to explain how this singularity, once its existence and underlying ontology were already given, blew up into the universe we see, beginning at 10^-43 seconds after the initial big bang). Many Worlds theory purports to account for these things by placing the universe - that is, the thing to be explained - inside a multiverse, and then fails to explain the multiverse. Yet, in order to explain a process that runs as part of an underlying process, the way local physical evolution (causality) runs as a part of global cosmic evolution, one must explain the underlying process right back to the beginning.
I can't help but be a bit taken aback when people who talk authoritatively about quantum mechanics, uncertainty, infinite-dimensional Hilbert spaces, infinitely-nested spacetimes and other clear manifestations of absolute freedom rail against UBT. Where do they think all of that freedom comes from? From constraint? Constraint is deterministic. Even if we posit the existence of a primal constraint which drives a deterministic many-worlds (relative-state) multiplexing of state and thus "creates freedom", what accounts for the nondeterministic (telic or aleatory) mapping of our consciousness into one particular history among the infinite possible histories thereby "created"? Again, we are forced to confront an inevitable fact: freedom is built into the microscopic structure of reality, and because the wave function is a stratified affair ultimately embracing the entire cosmos (regardless of the number of ulterior spaces in which our immediate reality is nested), it is built into the macroscopic structure of reality as well. Quantum mechanics, syndiffeonesis and UBT go together; remove any one of them, and all that finally remains is a teetering pile of paradoxes waiting to collapse.