The 1st Law of Thermodynamics states that a body can only gain or lose heat by taking it from, or passing it to, its environment or another body - this is because energy can neither be created nor destroyed.
How can the 1st Law be reconciled with the Big Bang's creation of matter/space-time and its energy? It looks as though either Thermodynamics has to go or the Big Bang has to go. And I think thermodynamics is here to stay, even if it says energy had to exist an eternal amount of time before the Big Bang. We could say there was no time before the Big Bang and therefore, no energy could exist. But that's just another way of saying the Big Bang created energy (when thermodynamics says it couldn't). And how can the death of the universe ever happen? Surely, that means energy will eventually be destroyed - something the 1st Law says can never happen.
Science can try to use the fact that, though energy can't be created or destroyed, it can change from one form to another - and thus create different laws of physics in other universes within the infinite and eternal multiverse. The universe you and I live in could thus have a beginning and end even though energy is neither created nor destroyed. This argument is mistaken. If energy changes form to create new laws of nature in another universe, that means the different universes in the spatially and temporally infinite multiverse would not be truly separate but would interact. They'd therefore constitute one system and be components in what could properly be called "the universe". The word multiverse would just be a red herring distracting us from an accurate description of reality, and we'd be living in an infinite, eternal universe.
If you and I are united with the cosmos in a comparable way to seemingly separate objects and events in a computer game being united (by strings of 1's and 0's), our lives cannot be limited to these bodies and brains we currently possess. We'd also be eternal.