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MWI is explicitly extra - spatiotemporal since it involves not just one spacetime, but many; i.e., a 'multiverse'. It also involves an ill-defined 'splitting' notion that is heavily dependent on FAPP decoherence arguments that aren't really adequate, since those pesky off-diagonal terms never really go away in that improper mixed state. All that is *more* radical than saying we have one world but there's more to it than meets the eye -- i.e., more than just the spacetime theatre.