As the Cosmic AC was not in space, but "in hyperspace and made of something that was neither matter nor energy", there should have been no objections to it taking the role of Maxwell's demon and reversing entropy, powering the universe through its hyperspace computational powers.
Asimov was a great popularizer of ideas that most people never come face-to-face with in a lifetime. And though some criticize his style, I always find it to be servicable and effective; he stays out of the way of his story.
On a side note: if you enjoy galactic timespanning of this sort, Alastair Reynold's "inhibitors" (a "race" of machines forming the backdrop of most/many of his novels) makes for some fascinating reading from a working astrophysicist. I found myself impatiently reading through the story, trying to get to the next bit of exposition where the Inhibitors are discussed. I wish he'd done even more of this. Ah well.
for those who've never read Asimov, this story is not really his best. his most famous and beefy works are the Foundation series and the Robots series, and highly recommended. They influenced many many things that came after, both in science and in science fiction. you can't call yourself a true SF fan unless you've read at least his main works.
for example: when I read HHGG for the first time, and the parts about the Deep Thought computer, I assumed it was inspired by and/or a humourous tribute/riff on Asimov, because there were so many strong similarities in structure and narrative techniques.
I thought that all energy is conserved. That is, if the sun dies, the materials that made the sun are not destroyed as such, thus, the sun can never die nor the universe.
I thought the ending was a really nice unification of scientific and religious thought, done in a novel way that I've never really seen before. If you don't like it, then I guess there's no other way to really argue for the story. I always thought that Asimov's strength in writing lied in his ideas, as opposed to his descriptions and writing ability.
Quite simply it's the twist in the last line. With an Asimov short story, you expect a twist anyway that forces re-evaluation of the characters and events, but The Last Question manages to transcend this and forces the reader to re-evaluate the nature of the external world (ie. outside the story itself, with some inter-textuality to the Bible thrown in).
The execution of this idea was also first-rate, IMO. The question 'can entropy be reversed?' acts as a brilliant 'hook' for the story as he fleshes out the history of the universe. He took a question usually too remote to be worth consideration in literature, and humanized it. And finishing on the Genesis quote was a stroke of brilliance.
The major themes here are ones that challenge us and are hard to cope with. Particularly the theme of inevitability. It is in the back of all of our minds and we condition ourselves to accept it, but it is always there. Asimov solves the inevitability of resource degradation by expansion and the inevitability of death by immortality, but in the end there are both, in fact, inevitable. When all seems lost and the bleakness of our existence is brought into scope, he presents the cyclic nature of time. A novel approach to a problem that plagues the core of our being. This is where the story really jumped from good to amazing for me. I'm still stuck on it.
The notion of the sun as the fundamental power source driving the earth was somewhat novel to me. I mean, we all know humanity wouldn't exist without the sun, but I hadn't thought of the stars as the batteries of the Universe before.
It may be novel to some computer scientists, but the idea can be found in any introductory ecology textbook.
It resolves the apparent 'paradox' between increasing entropy and increasing complexity of life: life thrives only because of the initial low entropy of the sun.
http://searchyc.com/submissions/last+question