There are quite a few theories about why we don’t see space aliens but here’s one that makes a lot of sense (assuming they exist): The Percolation Hypothesis holds that they can’t overcome the laws of physics any more than we can and that colonies would lose touch with the home planet due to slow communications, thus losing interest in space travel goals.
On the whole, as [Matt] Williams allows, the Percolation Hypothesis is a hard-headed look at the problem of why we don’t hear from ET. It does not invent a past or a psychological profile for life forms whose existence we cannot even verify. It simply assumes that, living in the same universe, they face the same physical problems we do. The physical problems that would be a barrier for us would function the same way for them.
Most science fiction gets around this problem by positing that the aliens have solved problems like faster than light travel, which we have no idea how to solve.News, “Is real-world space travel just too daunting for ET?” at Mind Matters News
But now, if there is a purpose behind the universe, maybe we and the aliens weren’t intended to meet. That was C.S. Lewis’s view:
That was part of the storyline in C.S. Lewis’s space trilogy, in which an Earthling finds himself on Mars (Out of the Silent Planet) and Venus (Perelandra). He soon discovers that Earth is quarantined from other planets because of the violence and other bad nature of its intelligent inhabitants (us).
Whether we find that an appealing explanation or not, there is plenty of evidence that humans might be a bad influence on more innocent extraterrestrials.News, “Is real-world space travel just too daunting for ET?” at Mind Matters News
You may also enjoy these accounts of why we do not see the aliens:
1.Are the Aliens We Never Find Obeying Star Trek’s Prime Directive? The Directive is, don’t interfere in the evolution of alien societies, even if you have good intentions. Assuming the aliens exist, perhaps it’s just as well, on the whole, if they do want to leave us alone. They could want to “fix” us instead…
2.How can we be sure we are not just an ET’s simulation? A number of books and films are based on the idea. Should we believe it? We make a faith-based decision that logic and evidence together are reasonable guides to what is true. Logical possibility alone does not make an idea true.
3.Did the smart machines destroy the aliens who invented them? That’s the Berserker hypothesis. A smart deadly weapon could well decide to do without its inventor and, lacking moral guidance, destroy everything in sight. Extinction of a highly advanced civilization by its own lethal technology may be more likely than extinction by natural disaster. They could control nature.
4.Researchers: The aliens exist but they are sleeping… And we wake them at our peril. The Aestivation hypothesis is that immensely powerful aliens are waiting in a digitized form for the universe to cool down from the heat their computers emit.
5.Maybe there are just very few aliens out there… The Rare Earth hypothesis offers science-based reasons that life in the universe is rare. Even if life is rare in the universe, Earth may be uniquely suited to space exploration, as the Privileged Planet hypothesis suggests.
6.Does science fiction hint that we are actually doomed? That’s the implication of an influential theory as to why we never see extraterrestrials. Depending how we read the Kardashev scale, civilizations disappear somewhere between where we are now and the advanced state needed for intergalactic travel.
7.Space aliens could in fact be watching us. Using the methods we use to spot exoplanets. But if they are technologically advanced, wouldn’t they be here by now? The Hart-Tipler conjecture (they don’t exist) is, of course, very unpopular in sci-fi. But let’s confront it, if only to move on to more promising speculations.
8.Is the brief window for finding ET closing? According to some scenarios, we could be past our best-before date for contacting aliens. Of course, here we are assuming a law of nature as to how long civilizations last. Can someone state that law? How is it derived?
9.What if we don’t see aliens because they have not evolved yet? On this view, not only did we emerge during a favorable time in the universe’s history but we could end up suppressing them. The Firstborn hypothesis (we achieved intelligence before extraterrestrials) lines up with the view that humans are unique but sees that status as temporary.
10.The aliens exist—but evolved into virtual reality at a nanoscale. That’s the Transcension Hypothesis, the latest in our series on science fiction hypotheses as to why we don’t see extraterrestrials.
On this view, after a Singularity the ETs become virtual intelligences, exploring inner space at an undetectably small scale.
11.Is intelligent life in the universe living in interior oceans of planets and moons? The Ocean Planets Hypothesis is that intelligent beings may flourish in the interior oceans of the moons of gas giant planets — or within exoplanets — but they are trapped there.
If intelligent life forms are trapped in the interior oceans of rocky moons and planets, Earth is a special planet—much better suited to space exploration.