I've heard many people claim that the first law of thermodynamics proves that the energy/matter must always exist in some form or another, since it cannot be created or destroyed. This would mean that energy/matter had no beginning, and will have no end. Is this a valid claim? Or is there something I'm misunderstand about the conservation law? And while I'm on the subject, I'd like to ask a few semi-related questions about the Many World's Interpretation of Quantum Mechanics. From what I understand, the MWI says that the random events of quantum mechanics "splits" the universe into different realities, one with each respective outcome of the random quantum event. My questions are: 1. Do physicists take the MWI seriously? Or is it just an imaginative hypothesis that probably isn't true? 2. Would the "universe splitting" of the MWI violate the energy conservation? Does it really create a new universe for each random outcome? 3. If the MWI is in fact true, could we then conclude that there exists an infinite amount of universes? Would it be true infinity, or just a really large number? Thanks.