Hundreds of billions of years from now, the universe will be undergoing an apocalypse – and aliens may already be hoarding stars to survive the coming doom.
Dark energy, a mysterious entity thought to make up 68 per cent of the universe, is accelerating the expansion of space. Eventually, galaxies will zoom away from one another so fast that nothing will be able to travel between them.
That’s not a concern right now, but an advanced civilisation with vast energy needs might have reason to worry. Dan Hooper, a physicist at the Fermi National Accelerator Laboratory, Illinois, has studied how this will impact a civilisation capable of harvesting stars for energy by building giant spheres around them and gathering them in a central location.
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Star harvest
Hooper found that if the civilisation can travel at 10 per cent of the speed of light, it would be able to hoover up stars in a sphere over 300Â million light years across before dark energy expansion makes going any further impossible. That is enough to encompass the entire Virgo supercluster, which holds thousands of galaxies, including our own Milky Way.
When you’re making plans on these galactic scales, the workings of dark energy are a serious concern – running out of usable stars is an existential threat, just as climate change is for current humans.
“If we knew that all the fossil fuels were only going to be there for another decade and then they’d be gone,” says Hooper, “I guarantee you we’d grab it all so we could use it eventually.”
Not everyone agrees. “The more natural, and easier and cheaper, thing to do would seem to be to expand as fast as possible and then just let the species expand away with the stars,” says Jason Wright at Pennsylvania State University.
Future proofing
Hooper readily acknowledges that projecting motivations hundreds of billions into the future is something of a stretch, but stresses that some things will never change. “Whatever you’re trying to accomplish – whatever that is – energy is going to be useful. That’s just built into the realities of the universe.”
What’s more, any alien civilisations currently engaged in star-hoarding might be easy to spot. For one thing, getting a star to move across the cosmos would take a lot of energy, likely resulting in the emission of bright light.
The ideal stars would all be relatively similar in size and age, not unlike our own sun. “If you found a group of galaxies that had certain combinations of stars and not others,” says Hooper, “that could be an interesting signature of this phenomenon.”
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