What I don't like about many worlds is that it's spectacularly inefficient w.r.t. energy. A whole new universe is created for each option. That's very wasteful and doesn't gel with so much of what we see around us. Sure, you can say that energy is fixed within each universe but not in the whole system, but that sets off my internal Occam's Razor.
You also don't just have two worlds, you have infinite. In the coin-flipping example, whenever a coin is flipped there are many other universe-splitting this-or-that events happening elsewhere in the universe at the same instant. So each instant there are infinite worlds created (or infinite x infinite to describe each combination), and again a split in each universe in the next instant for every next possibility. Mmm. Dodgy.
My favourite: John Cramer's Transactional Interpretation. Doesn't require infinite universes' worth of energy, doesn't require an observer to collapse multiple possible waves. Does require you to accept backwards-in-time communication (breaks causality) but brings some very interesting what-if questions.
You also don't just have two worlds, you have infinite. In the coin-flipping example, whenever a coin is flipped there are many other universe-splitting this-or-that events happening elsewhere in the universe at the same instant. So each instant there are infinite worlds created (or infinite x infinite to describe each combination), and again a split in each universe in the next instant for every next possibility. Mmm. Dodgy.
My favourite: John Cramer's Transactional Interpretation. Doesn't require infinite universes' worth of energy, doesn't require an observer to collapse multiple possible waves. Does require you to accept backwards-in-time communication (breaks causality) but brings some very interesting what-if questions.
http://en.wikipedia.org/wiki/Transactional_interpretation
http://en.wikipedia.org/wiki/Causality