Exploration: an essential key to survival
Why would a technological civilization (such as ourselves) want to colonize other worlds? Some would argue against this saying: given the mess that we have made of our own planet, what gives us the right to trash another? Indeed, in the Bible and ancient Greek mythology, it is taught that the ascension of humanity into the skies and heavens is forbidden for exactly this reason —it's better for the corruption of our species to be confined to just the Earth. Yet, in other mythologies and some religious stories, it is said that it is our destiny to reach the heavens.
But still, this point is more relevant than ever as we rush towards total social and environmental collapse. But I am hopeful and optimistic that we'll fix our problems down here on Earth before we colonize other worlds. And thus, going back to our original question, we won't consider trying to escape the mess that we ourselves created (or another technological civilization trying to escape the problems they inflicted upon themselves) a reason for colonizing other worlds. Ironically, even if a technological civilization were not a danger to themselves, the universe itself endangers any technological civilization and is, in the long run, a threat to their own survival. Take, for example, the threat of the solar system to humanity, in the long run. If our species posed no danger to itself and left the environment more or less undisturbed, we
would be safe for a little while; but despite an asteroid impacting the Earth being very unlikely in the short term, such an impact is, for all practical purposes, inevitable in the long term. Thus, it is desirable to colonize other worlds in the solar system just as a strategy for staying alive. And after a really long time, the Sun will eventually turn into a Red Giant rendering the Earth uninhabitable. With that fact in mind, finding refuge on other worlds becomes very desirable (or, to be more accurate, essential) indeed. In the long term, not even an advanced civilization's solar system will stay safe. For example, a nearby supernova could potentially render all species of life in another nearby solar system extinct. For billions of years, our ancestors evolved (according to Darwin's theory of natural selection) to do whatever it required to stay alive. It will be no different for advanced technological civilizations: they will spread throughout their solar system and eventually entire galaxy as a strategy for staying alive.
Civilizations near the end of time
And in the really long run, all of the stars in the universe will die and cease to shine—even the tiny red dwarfs and neutron stars which will shine for many trillions of years. At that point in history, unless advanced civilizations are capable of harnessing vacuum energy, they will have had to migrated to a black hole in order to continue powering their civilization. Here, they would construct some kind of artificial habitat (such as an O'Neil cylinder depicted above) to live in that orbits around the black hole. Such a future civilization would extract energy from the black hole either from the conversion of the habitat's gravitational potential energy into kinetic energy as it falls towards the black hole, through tidal forces exerted on the habitat by the black hole, or by extracting its energy through Hawking radiation. I was fortunate enough to have had helped produce a video for Isaac Arthur's YouTube channel, Science & Futurism, which gives a very detailed analysis of how an advanced civilization might live around such a black hole.
But in the even longer run, black holes will eventually evaporate due to Hawking radiation and the universe itself will become uninhabitable as it reaches its entropic heat death. Then, the universe will be cold, dark and lifeless. Around this time, all of the atoms comprising ordinary matter will have had been torn apart by repulsive forces caused by the expansion of the universe. To survive, the long descendants of humanity would employ the same strategy as that used by their hunter-gatherer ancestors and humans living around the time that the Sun began to swell into a Red Giant: spread outward. For our hunter-gatherer ancestors, survival was a matter of leaving Africa; for humans living on the inner-most planets, moons, and asteroids five billion years from now when the Sun "burns the Earth to a crisp or reduces it to a whirl of atoms," they will have had to colonize worlds farther out in the solar system in order to survive. But in the case of a civilization living quite literally near the end of time close to the universe's death, to survive they would have to travel through a traversable worm hole (connected by two black holes) to another universe—a voyage through hyperspace. They would likely travel to a "nearby" universe with similar laws of nature to our own, but one that is much younger than our own full of stars and planets.
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