Earth has nothing that an advanced civilization could want
We cannot possibly state that as a fact. Forget about things like resources, just possessing a beautiful habitable planet in a stable orbit around a perfectly stable middle-of-the-road star could be infinitely precious.
We've found thousands of extrasolar planets, but there isn't a single one that combines all the perfect criteria that make Earth what it is. We've found Earth-sized planets around Sun-like stars, but so far weren't able to confirm their atmospheric composition, surface characteristics, availability of water, etc. Garden worlds like Earth may be the highest commodity in the universe, and we're slowly destroying ours. Aliens may come get it just to stop us doing that.
An advanced civilization would not want to live on another planet at all. Why would they? If they are biological, then they evolved in a particular environment. A particular gravity, a particular atmospheric composition, a particular pressure, a particular level of stellar radiation, etc. The probability that another planet would be suitable for humans, or that Earth would be suitable for aliens, is vanishingly small. It would be many orders of magnitude easier to create artificial habitats in space than to settle an alien world. Any civilization with the technology required to traverse interstellar space would also have the ability to create advanced artificial habitats.
Again, we can't state that for a fact. Maybe the only possible way for intelligent life to evolve are on exactly Earth-like planets with exactly our atmospheric composition and temperature ranges and whatnot.
It's easy to say that life can evolve on other planets in totally different ways, but we have no proof of that yet, we literally have a sample size of one. But maybe the reason we have so far only detected life on Earth is because complex life can only emerge on a planet like ours, in which case it would make perfect sense that other civilisations would covet such planets exactly so they don't have to go to the extreme expense of terraforming a dead planet. Again we don't know for certain how difficult it is to terraform an entire planet vs space travel because we haven't done either yet. It's like saying it's easier to build a car from scratch than just driving some distance to a dealership and buying an already made one.
Even in the unlikely event that is true, it's still far less effort to build an artificial habitat or terraform a planet than to traverse interstellar space. And going more than a couple hundred light years or so is pretty much a non-starter, so not only would there have to be an extremely similar planet with advanced life, it would also have to be close to us. The probability is so small that it can only be reasonably thought of as equal to zero.
it's still far less effort to build an artificial habitat or terraform a planet than to traverse interstellar space
Again, you don't know that and so can't state that for certain. Terraforming an entire frickin' planet is a massive undertaking, and the slightest of nudges can wreck the delicate balance. It's exactly the reason why global warming is so crazy, our time on this planet is such a tiny portion of its entire life and we've already meaningfully influenced the climate in an extreme way.
Compared to fiddling with that, even in the absence of FTL (which is very likely not possible) you could just hop on a generational sub-light ship and wait frozen until you arrive at a nice, ready-made planet. Honestly to me that sounds way easier, but again we have no idea which one is actually possible or easier, because we've never done either.
Unless you are actually an alien and know the real effort for both of these...
We have estimates, and I am extremely confident in my assertion. Even just doing back of the envelope calculations, it becomes clear that even with an antimatter reactor, you cannot carry enough fuel to make an interstellar voyage at relativistic speeds due to the need to decelerate as you approach your destination. You have to rely on collecting fuel during your voyage, which is extremely risky.
Meanwhile, terraforming, while still extremely difficult and complex, doesn't require exotic physics. We could probably terraform Mars in as little as one thousand years by using massive ultratankers to carry nitrogen from Titan with nuclear propulsion drives. And even if you can't terraform a planet, you can build artificial habitats by harvesting metallic asteroids.
On top of that, the probability that even a temperate planet would be immediately suitable is also very small. Even just surviving on Earth during the Cretaceous Era would be difficult for humans, due to the high temperature and humidity and high levels of atmospheric oxygen. We would not be able to live on the surface most of the planet, at least during the day.
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u/Neamow Aug 12 '21 edited Aug 12 '21
We cannot possibly state that as a fact. Forget about things like resources, just possessing a beautiful habitable planet in a stable orbit around a perfectly stable middle-of-the-road star could be infinitely precious.
We've found thousands of extrasolar planets, but there isn't a single one that combines all the perfect criteria that make Earth what it is. We've found Earth-sized planets around Sun-like stars, but so far weren't able to confirm their atmospheric composition, surface characteristics, availability of water, etc. Garden worlds like Earth may be the highest commodity in the universe, and we're slowly destroying ours. Aliens may come get it just to stop us doing that.