The question of whether the universe is eternal or not is a topic of ongoing scientific and philosophical inquiry. Our current understanding suggests that the universe had a definite beginning known as the Big Bang around 13.8 billion years ago. However, what occurred prior to the Big Bang remains a subject of active research and speculation.
As for who or what created the universe, it is a question that falls within the realm of metaphysics and theology, rather than scientific inquiry. Science seeks to explain the natural world through empirical observations and testable hypotheses, whereas the concept of a creator lies in the realm of belief systems and personal interpretations.
Regarding the concept of the "heat death" of the universe, it is a hypothesis based on our current understanding of the universe's expansion and the behavior of energy. The idea suggests that as the universe continues to expand, the energy within it becomes more and more spread out, leading to a state of maximum entropy or disorder. This hypothetical end state is known as the heat death of the universe.
In the scenario of heat death, all available energy would be uniformly distributed and no longer available for useful work. It is a state of thermodynamic equilibrium where there would be no temperature differences or gradients, making it impossible for any processes or interactions to occur. However, it's important to note that this is a theoretical prediction based on our current understanding, and our knowledge and understanding of the universe may evolve and change over time.
It's worth mentioning that there are alternative theories and possibilities about the future of the universe, such as the Big Crunch, the Big Rip, or even the concept of a cyclical universe. Scientific research and observations continue to shed light on these questions, but definitive answers remain elusive at this point.