What would very advanced alien civilisations do with the cosmos? Sure, at the moment that’s very much guesswork, but at this point in time we can at least start doing some reasonable guesses.
There is one insight, that has hardly entered the consciousness of scientists, futurists and science-fiction writers: Even though nuclear fusion is great, it’s probably not the best physically possible source of energy. Why? Because nuclear fusion only converts a very small fraction of the mass of nuclei into energy. Higher conversion rates can be found around black holes. So, very advanced civilisations might harness energy from black holes. Or they could even build artificial black holes. That idea is explored in the following, very intriguing video:
An alternative way of converting mass to energy is depicted in the science fiction story “Hot Rock” by Greg Egan. In that story, regular matter is slowly converted into highly degenerate matter, extracting almost all energy out of that regular matter in the process.
Perhaps very advanced civilisation will develop even more efficient and mind-boggling ways for generating energy. Nuclear fusion is quite likely not the pinnacle of energy production.
Let’s get rid of stars
Now, this may have very wild consequences for the existence of stars, which produce most of their energy with nuclear fusion. If there are better ways to generate energy, why be content with those huge plasma balls that spew light and particles into all directions without being optimally efficient? Wouldn’t it be better to transform them into optimally efficient mass energy conversion engines that can be controlled at will? Yes, indeed that would seem quite likely, if it turns out to be technologically possible. It’s also plausible that those “stellar superengines” will have some similarities with black holes, but with the difference that they don’t form a largely visible accretion disk. At our current stage of development we might even confuse those engines with dark matter.
Anyway, we would be assume that alien civilisations that expand throughout the galaxy will turn most stars into those superengines. The consequence will be a very dark galaxy – perhaps comparable to the galaxies found recently mostly consisting of dark matter?
Perhaps don’t throw away all stars
There might still be a reason to conserve some stars. Advanced civilisations might want to study life emergent on planets in a way that is as natural as possible. They might therefore conserve those (and possibly nearby) stars, in order to study the evolution of life. Probably they would do most of those studies in simulated worlds, but it might be a good idea to keep some samples of real stars and planets around for comparison, or other reasons. In other words they would keep some nature reserves that contain natural stars and stuff. If that’s true, and there are indeed advanced alien civilisations out there, the conclusion is, that we most likely live in such a nature reserve (or a simulation).
But now you will say: That’s not possible, because we see lots of stars out there in our galaxy. The answer to that is: They are fake. The aliens want us to believe that we are in a natural, virgin cosmos. Why? Perhaps because that situation is more natural, or more conducive for making us want to advance to the interstellar level. If there were no stars out there, we would find the outside cosmos boring, like “there’s nothing out there, so why leave Earth or even our solar system?” The mechanism by which they create the false impression of natural stars in the cosmos for us is not clear. Perhaps they create holographic fake stars, or a “star tapestry” around Earth or our solar system, or they manipulate our minds in order to make us “see stars”.
In any case, once we will be able to penetrate that “star tapestry”, we should expect to see way fewer stars out there. Instead, the near cosmos should be dominated by superengines, and computronium arrays surrounding those – or embedded within those.
That certainly sounds strange to us, at least at our current level of development. Nevertheless, reality often turns out to be weirder than our wildest imaginations. So, the future will remain mysterious and interesting.