Dan Hooper, a senior scientist with Fermi National Accelerator Laboratory has written a paper outlining a way future aliens could keep their civilizations alive in spite of the isolation due to an expanding universe. In his paper uploaded to the arXiv preprint server, he suggests they might consider collecting and storing stars.

A Dyson sphere is a theoretical structure able to house a star. Originally proposed by Freeman Dyson, the sphere was originally envisioned as a group of satellites completely encompassing a star to capture all of its energy. That energy could then be used for whatever purposes the civilization that created it desired. In this new effort, Hooper suggests aliens might be creating similar structures to provide power once the universe expands to an untenable size.

Prior research has shown that the universe is not just expanding, it is picking up speed as it does so due to dark energy. This means that almost everything in the universe is being flung farther apart from everything else. Such a scenario suggests that galaxies will become increasingly isolated, though the components of the galaxies will remain bound by gravity. So, Hooper wonders, what would an alien race do to ensure it has a steady source of power? He suggests they might be collecting stars at this very moment, getting ready for the days ahead when they will be too far away to grab.

Hooper notes that such a scenario is still very far off—on the order of 100 billion years from now. But he also notes that if aliens were grabbing stars from one galaxy and transporting them back to another, the time for each trip would be on the order of billions of years. Thus, they would have to be doing it now, before they run out of time. He acknowledges that humans would probably not be able to understand the mechanics of moving a star, but muses on the possibility of an alien race powerful enough to do so. He further suggests that if such activity is currently happening, we might be able to see evidence of it by looking for stars that seem to be moving between galaxies—or by looking for holes in galaxies where stars have already been removed.

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