That is the most commonly accepted theory at the moment. But remember, they also thought until about the turn of the century that the universe was slowing down. On an infinite timescale and accepting the idea thst the sun is nuclear, sure everything we are will one day extinguish. But that is just one theory with wide acceptance. On the other hand, our star is much more stable than other stars and admittedly we don't really know the true nature of the sun. Our knowledge of the true nature universe is somewhat limited. We could be wrong. As far as we know all laws of physics might break down at the edge of this universe. I very much appreciate your input.