First, there was light.
This is, what is written in the Bible. Scientists have a quite similar view- with the Big Bang, an enormous blast of energy evolved and formed the universe as we know it today. Energy, which is still present- either floating around or bound in matter as entropy or constantly regenerated by stars and other objects. Nothing is lost. The laws of thermodynamics are valid everywhere. The most sustainable concept you can imagine.
What has been before- nobody knows. What will there be at then end? Speculation. A big dark space of entropy. Maybe. irrelevant as well at the moment. Which will last beyond our imagination.