If energy can’t be created or destroyed why do people think that a universe made up of energy could have a beginning or an end?
Because change happens. No beginning and no end imply timelessness. In this view the universe always existed. Timelessness would imply no evolution. Many philosophical ideas have this concept of timelessness. Ancient Eleatic philosophers, Parmenides and Zeno were famously supporting this view that there is no change. Change is an illusion. Heraclitus, a pre-Socratic philosopher took the opp view that world is driven by constant change and famously said that you can't step into the same river twice. Their views had strong influence on Socrates,Plato and Aristotle who tried to reconcile change and permanency. For example Socrates conceptualised a world of senses and a world of forms In eastern philosophy as well there are similar thoughts in which reality is said to be permanent and unchanging and the world which is changing is said to be an illusion. It is real but not the ultimate reality. This view strongly contradicts with what we observe. The universe is const...