How does energy exist if it cannot be created nor destroyed?
The fact that energy can neither be created nor destroyed is mathematically equivalent, in classical physics, to this statement: “the laws of physics governing this system aren’t changing.” Presumably at the beginning of the universe, the laws of physics themselves were beginning, just as space and time were. In such a situation, conservation of energy would indeed be totally violated, and thus we would have an escape: energy /can/ be created or destroyed when the laws of physics are changing. (To give a trivial example, if you raised the gravitational constant G, a bunch of potential energy would be created in the universe. It would not be much different from how we today use gravitational slingshots, which basically work on the principle that when you pass behind a planet as it travels, it “lifts up” your gravitational potential energy as it travels away from you.
