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There's one thing that's always bothered me about the Fermi paradox, and that is the idea that since we can't see evidence of colonization of intelligent species, then there must be some great filter that stops species like ours from proliferating throughout the galaxy.

It just feels so presumptuous. Like we can't see very well beyond our own solar system. Sure, we can see very bright things like stars, but we can't really "see" exoplanets. We can detect them by how they interfere with a star's gravity and light but we can't see enough detail to know if they have life or not. Heck, we have trouble doing that with planets, dwarf planets and moons in our own backyard.

Why couldn't there be a massive galaxy spanning civilization in the Milky Way? What makes us so sure we'd be able to detect it now with our satellites and telescopes? Is it possible they've simply overlooked us as being just another planet among a hundred billion other planets? Or they see earth and don't want to mess with it, the way some conservationists on Earth try to save patches of wilderness? Maybe they don't communicate in radio waves, if they somehow travel FTL, then they'd have to communicate FTL and that would exclude radio wave communication. They could view radio waves as we view homing pigeons. Even if they don't travel FTL and colonize using generational starships, maybe they still have moved on from radio waves.

Is there any reason to support the Fermi Paradox? To me it seems we simply don't know enough about our own galaxy to even start making such claims right now.

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    $\begingroup$ Once you start talking about FTL, you're imagining alternative laws of physics. Nobody can give a scientific answer based on hypothesized alternative physical laws. $\endgroup$
    – user15381
    Aug 5 '21 at 18:51
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    $\begingroup$ The "Fermi paradox" has lots of potential solutions that are a mouse-click away. $\endgroup$
    – ProfRob
    Aug 5 '21 at 20:15
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    $\begingroup$ Given that we've only discovered one example of a planet with life (Earth), I don't see how astronomers could provide a scientific answer to this question. $\endgroup$
    – Connor Garcia
    Aug 5 '21 at 20:32
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The claim in the Fermi Paradox is that universe is so big, with so many stars, and so old, that even if the probability of life, civilisation and interstellar travel is tiny for each star, there must be a lot of civilisations doing interstellar travel and sending proves and signals across the galaxy, if not colonising it, and therefore we should be able to detect some of them.

Some objections to the Fermi Paradox argue that such civilisations aren't so common nor long lived and therefore they would agree with your reasoning.

More information on https://en.wikipedia.org/wiki/Fermi_paradox

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  • $\begingroup$ This is a good answer, but it could be improved by making a more careful distinction between "universe" and "galaxy," which is also something that the OP was careless about. $\endgroup$
    – user15381
    Aug 6 '21 at 15:44
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The Fermi paradox isn't meant to make you conclude that there is some kind of great filter. The Fermi paradox is just the contradiction that arises when comparing the fact that we have not observed any extraterrestrial life yet, with the number of extraterrestrial species that we should observe according to some reasonable estimations.

The conclusion is not univocal, the point of the paradox is to make us think and propose different solutions. It could either be a great filter, or that life itself exceptionally rare, or some other theories like the ones you describe. At the moment we don't have an answer, and the paradox serves to propel us forward in seeking it, by asking one of the most fundamental questions in science: why are things like that? could they be different?

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The Fermi Paradox may have been intended to question basic assumptions and examine the factors related to colonization in the galaxy. To begin, the paradox statement is, presumably, where are they? Where are these colonizers and why haven't they been here? Lets assume that everything we currently know regarding the physics of the universe, is also known by another advanced civilization in the galaxy. Even though the speed of light is such a slug, FTL travel is not a consideration. Lets also assume that they have escaped, so far, encountering the great filter. We have no idea how old this civilization is, but we can assume they have reached a state of technological advancement sufficient for space travel. Our own civilization, in its nascent way, is at this threshold.

Among things that have to be thoughtfully examined, are other basic assumptions and considerations regarding the state of this civilization, and the practicality of interstellar travel. Even though we have no knowledge of how the life form of this civilization evolved, we would have to assume that they are of a form capable of developing advanced technology and that they have readily available materials needed to carry on this development. Further, we would have to assume that this civilization would be constrained by the same economic considerations that would restrain interstellar travel, namely the prohibitive cost in resources and time of single mission ventures to reach another star system with habitable conditions. Consequently, we are looking at an advanced civilization much older than ours; a civilization that has likely colonized space rather than ventured to a particular place. And in fact, in achieving such colonization they may not have left their home planet because they have been able to conquer all deficiencies and meet all needs required for this advanced technological state. They may have no need to colonize space, but to colonize a single place.

Deep-space communication by means other than radio is an interesting idea, but one thing that has to be kept in mind. Whatever means is used to communicate across vast distances, the speed of light will be a limiting factor in the time taken by transmissions. If radio is used, we already know that transmissions will likely be in the vicinity of the 21 cm hydrogen-band quit zone. This is because galactic and terrestrial atmospheric noise is minimal in the radio background near the 21 cm radio-emission band of hydrogen. In fact, if we assume our state of radio transmission and reception is equivalent to that of another more advanced civilization, the only question remaining would be how they use radio in communication. What are we supposed to be listening for?

We may wish to consider that among the issues raised by the Fermi Paradox is that other advanced civilizations elsewhere in the galaxy are likely looking for us for the same reasons we are looking for them. They have encountered the same limitations in technology that we face. They have encountered the same limitations in physics, the same limitations in the vastness of the galaxy, the same considerations we are having about the existence of life elsewhere in the galaxy. There is no reason to consider that the Fermi Paradox, and its ramifications, are presumptuous. Rather, the Fermi Paradox simply lays out an array of issues and assumptions, and asks that we deeply think about this problem with careful, unlimited, scientific consideration.

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