# Are Aliens Visiting Earth? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [June 25, 2020, 10:13am UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949 "2020-06-25T10:13:36Z")\ **Posts on this page:** 20\ **Page:** 10
**Author:** ![eburacum\_45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum_45/32/3385_2.png) [@eburacum\_45](https://boards.straightdope.com/u/eburacum_45)\ **Post date:** [May 3, 2021, 9:52am UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/182 "2021-05-03T09:52:58Z")
> [@Cervaise](#): > > Millions of years is an infinitesimal fraction of the overall scope of time within which civilizations would need to overlap for the engineering even to matter. That’s the key point and it can’t be handwaved away. You are thinking on too short a timescale. A Dyson swarm around a red dwarf star might be dynamically unstable, but it would only take a fraction of the available processing power in such a structure to maintain the swarm using station keeping; this situation could last for trillions of years, until the star itself dies. The light-speed delays within such a structure could favour a very slow existence for such an entity - if it takes twenty minutes for the entire structure to formulate a single, coherent thought, that might mean that a trillion years could pass on a much shorter subjective timescale. Since we don’t see any evidence for such structures, I think some other factors need to be accounted for. All suitably advanced civilisations will want and need to plan for the deep future - if they are not building trillion-year Dyson swarms, they must have better ideas. Or they don’t exist, which is entirely possible. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [May 3, 2021, 10:03am UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/183 "2021-05-03T10:03:50Z")
Yeah and I thought of a simpler way to phrase my previous point: Deep time can only be a _problem_ for the Fermi paradox, it can’t be the solution, Because either species can reach across deep time (or leave relics or whatever), or they can’t. If they can, then that is yet more civilizations that could have left visible evidence for us to see, but, for unknown reasons, no such evidence has been verified. If they can’t then the situation is exactly the same as if there was _not deep time_. Why do we not see evidence of ETs in our time window? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [May 3, 2021, 5:43pm UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/184 "2021-05-03T17:43:30Z")
> [@Mijin](#): > > - Ok, when we’re talking millions of years then even materials that seem stable to us are not, eg diamond will become graphite. But the engineers making a ship designed for millions of years will be aware of this. This (subsequent timescale correction noted) is the kind of thing I have been alluding to; it’s one thing to be aware that materials inevitably degrade in deep time, but it is quite another thing to have a solution or workaround for that. Repair is an option, but requires power sources, which degrade, and are impossible to refuel mid-journey. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [May 3, 2021, 5:48pm UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/185 "2021-05-03T17:48:50Z")
> [@Mijin](#): > > Deep time can only be a _problem_ for the Fermi paradox, it can’t be the solution, > > Because either species can reach across deep time (or leave relics or whatever), or they can’t. > > If they can, then that is yet more civilizations that could have left visible evidence for us to see, but, for unknown reasons, no such evidence has been verified. > > If they can’t then the situation is exactly the same as if there was _not deep time_ . Why do we not see evidence of ETs in our time window? To paraphrase Terry Pratchett, perhaps for the same reason that people in Trafalgar Square can’t see England. Maybe we’re it. Not a new idea, but what if panspermia is it - the spread of ‘probes’ is actually just the seeding of simple life or its precursors - produced in vast number by a planet teeeming with life, sufficiently so that by sheer weight of numbers, a tiny few last long enough to make it across the void inside rocks or chunks of ice, to a different system, not even deliberately. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [May 3, 2021, 6:05pm UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/186 "2021-05-03T18:05:54Z")
> [@Mangetout](#): > > This (subsequent timescale correction noted) is the kind of thing I have been alluding to; it’s one thing to be aware that materials inevitably degrade in deep time, but it is quite another thing to have a solution or workaround for that. Not all materials will degrade significantly within this timeframe though, so there is no fundamental physics that prohibits such a probe being built. So, once again, you’re talking about engineering challenges, which are largely irrelevant to the Fermi paradox. > [@Mangetout](#): > > Not a new idea, but what if panspermia is it - the spread of ‘probes’ is actually just the seeding of simple life or its precursors - produced in vast number by a planet teeeming with life, sufficiently so that by sheer weight of numbers, a tiny few last long enough to make it across the void inside rocks or chunks of ice, to a different system, not even deliberately. Sure, that’s a possibility. It’s not a solution to the Fermi paradox (and also, I’m not sure how it relates to the post you’re responding to), but yeah, in principle life could be seeded to many star systems from a single origin. There are earthly bacteria that seem to be able to survive space in a “just add water” state. And, encased in rock, could hypothetically survive re-entry. ---
**Author:** ![echoreply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/echoreply/32/3641_2.png) [@echoreply](https://boards.straightdope.com/u/echoreply)\ **Post date:** [May 3, 2021, 8:54pm UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/187 "2021-05-03T20:54:08Z")
> [@Mijin](#): > > If they can’t then the situation is exactly the same as if there was _not deep time_ . Why do we not see evidence of ETs in our time window? Because life in the universe is simply not common enough for us to continuously be contacted by aliens. I think the deep time thing is an explanation that life _can_ be out there, and even somewhat common, but not common enough to overlap with us both temporally and spatially. How long has it been since we’ve had the technology to detect, and the ability to reliably record an alien visit (probe or otherwise)? Maybe 100 years? Sure, maybe a probe visited 1000 years ago, and some monks wrote it down, but now we’re into von Däniken territory. Maybe a probe is flying through our solar system right now, but it’s too dark and radio silent, so we just don’t know. Maybe there was a civilization that broadcast radio waves for thousands of years, but the signals all reached earth 50 million years ago? So in order to ignore deep time we have to say there are so many alien civilizations, or at least one of them is so large and active, that they are sending probes, radio waves, light, or gravity waves to us essentially continuously, so we don’t miss them. Why isn’t the galaxy just grey goo? ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [May 4, 2021, 4:52am UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/188 "2021-05-04T04:52:36Z")
> [@echoreply](#): > > So in order to ignore deep time […] I didn’t say ignore deep time. The point is, it doesn’t help in terms of the Fermi paradox, it’s just more civilizations that could leave something for us to see. If we’re positing that life is so rare that there is only one example of it in our galaxy in the last billion years then _that_ is the solution being suggested for the Fermi paradox. > [@](#): > > […] we have to say there are so many alien civilizations, or at least one of them is so large and active, that they are sending probes, radio waves, light, or gravity waves to us essentially continuously, so we don’t miss them. Not really no. Any civilization just needs to do anything that is detectable to us now. That could be a megastructure, including Dyson spheres, but also megastructures that we couldn’t understand the function of. It could be a legacy of probes around all stars. Or beacons using stellar radiation to broadcast messages for as long as the star is around. For a very advanced civilization it could be some kind of modification to stars or the galaxy itself. Species don’t need to be contemporaneous, and they don’t need to have specifically sent a message to humans. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [May 4, 2021, 7:35am UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/189 "2021-05-04T07:35:54Z")
> [@Mijin](#): > > Sure, that’s a possibility. > It’s not a solution to the Fermi paradox (and also, I’m not sure how it relates to the post you’re responding to), but yeah, in principle life could be seeded to many star systems from a single origin. There are earthly bacteria that seem to be able to survive space in a “just add water” state. And, encased in rock, could hypothetically survive re-entry. Mechanical parts seize; electronics get fried; both require refining and manufacturing infrastructure to boot up their production. A self-replicating probe would need to be able to manufacture copies of itself with very little external support, making its own parts from common chemicals. We have an example of self-replicators that already do that right here. Where is everybody? We’re here - we just forgot we’re ‘everybody’. Interstellar probes with the objective of spreading across the galaxy would seem to need mission objectives comprising: 1. **Replicate** - make more probles 2. **Spread** - make the new probes go places 3. **Adapt** - be able to use variations in raw materials; be able to exploit different energy resources and 4. **Do something probe-y** - build something to transmit information home, maybe. Small, adaptable things will accidentally evolve - through adaptive mechanisms built into them, or through mutation caused by damage; functions can be lost or added. If they lose the function for objective 1, they die out If they lose function 2, they don’t spread If they lose function 3, they will be outcompeted by their siblings If they lose function 4… they lose a _burden_ - they become simpler to make, potentially smaller, lighter, more durable and less expensive in terms of resource demand and more competitive for those resources than their siblings that are still trying to build transmitters or whatever. It’s an _advantage_ for self-replicating adaptive probes to stop doing the ‘probe’ objective. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [May 4, 2021, 9:22am UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/190 "2021-05-04T09:22:28Z")
> [@Mangetout](#): > > Mechanical parts seize; electronics get fried; both require refining and manufacturing infrastructure to boot up their production. This is beyond painful at this point. You surely must know by now what I’m about to say: **Engineering problems are irrelevant to the Fermi paradox** We are talking about aliens that most likely will have spent, conservatively, _millions of times_ longer on space technology than the mere decades that humans have so far. What engineering blocks that humans currently have can we be confident will still be blocks over that timeframe? The answer is: Only those things that are fundamental limits of physics. And even then, probably some of the things that we think of as fundamental limits are actually not with a fuller understanding, but we need to at least begin from that set of things thought to be impossible in principle. There is no fundamental physical reason that we are aware of that a machine lasting millions or even billions of years could not be constructed. I hope your next post directly responds to this point. Not just yet another repeat of your skepticism, which is not an argument. ---
**Author:** ![AlienBabble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alienbabble/32/3344_2.png) [@AlienBabble](https://boards.straightdope.com/u/AlienBabble)\ **Post date:** [May 4, 2021, 10:22am UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/191 "2021-05-04T10:22:20Z")
Triangle-shaped UFO vexed UK military in 2016. An unprecedented response to the sighting and the subsequent alleged cover-up: [![](https://img.youtube.com/vi/VJTGpxOqzjA/maxresdefault.jpg "The Pentyrch UFO Incident | Documentary Special") ](https://www.youtube.com/watch?v=VJTGpxOqzjA) ---
**Author:** ![Grrr](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/grrr/32/146_2.png) [@Grrr](https://boards.straightdope.com/u/Grrr)\ **Post date:** [May 4, 2021, 10:42am UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/192 "2021-05-04T10:42:38Z")
The idea that we have a basic understanding of the fundamentals of physics seems dubious to me. Until we understand more about quantum science and how to connect it to physical science we really know nothing for sure. And this assumes the human brain is even capable of understanding quantum science in any meaningful way. Maybe time isn’t such a hurdle to supposed aliens that have a better understanding of quantum science. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [May 4, 2021, 1:45pm UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/193 "2021-05-04T13:45:06Z")
> [@Mangetout](#): > > Indeed, but you shouldn’t use such argument to automatically wave away the idea that limits can and do actually exist. The half life of isotopes isn’t likely to be something we’re just going to work around, for example. But we’d have to actually see examples of such limits, not just assume that they must be there. The half life of Thorium is ~14 billion years, unless we are talking about timescales in that range, it _is_ something that can be worked around. > [@Mangetout](#): > > “Oh, but people thought their breath would be sucked away if they travelled more than 30mph” is often used as an argument against c being a fundamental limit of speed, but the two ideas are not the same at all. Maybe by some, but that’s not an argument that anyone is making in this thread, so I don’t know why you would try to invoke it here. There are actually well understood laws of physics that explain why we almost certainly cannot travel faster than C. The “can’t travel faster than 30mph”, which was not a position held by many at all, and was not based on anything like robust science, just individual incredulity. > [@Cervaise](#): > > One of the assumptions of looking out among the stars for other civilizations is that they are there _right now._ (Well, “right now” meaning the arrival of their light in our neighborhood where we can see the evidence.) But who’s to say the extraterrestrial civilization has reached a peak in its development, such that its technologies and other impacts can be observed, _simultaneous_ to our ability to observe them? Then where did they go? Are we saying that there is a limit to how long a civ can last? What reasoning is this based on? > [@Cervaise](#): > > It seems vanishingly unlikely for any such civilization, once it appeared, to have persisted for so long. More likely that they would have destroyed themselves, or transcended their original form, or naturally died out, or something else that exceeds our capacity to imagine because we are simply not equipped to think about events on this kind of time scale. I don’t think that there is anything that gives any evidence to these suppositions. > [@Cervaise](#): > > In my own mind, I think about it like this: You’re at the top of a skyscraper with a bucket of ping-pong balls. You spend the next month randomly throwing them off. What are the odds that two of them will hit the ground at the same time? It’s not impossible; you can speculate on a number of local factors that could influence the falling times of all the different balls and create a simultaneous landing. But it’s _wildly_ improbable. I have a slightly different thought experiment. You have a continent sized plain of grass. Every few years, you drop a small group of rabbits in a random location. What are the odds that two of these groups encounter eachother. Sure, some will die off, some will stabilize their population, but unless you can explain why _all_ of them would, then you would expect that in a few hundred or thousand years, the continent will be covered with rabbits. > [@Cervaise](#): > > TLDR — there’s a lot of discussion in the thread about interstellar distances, which are vast, but the mind-melting scale of billions of years is just as significant, if not more so, for creating gulfs of inaccessibility between hypothetical pan-galactic cultures. They also give plenty of time for the improbable to happen. It seems as though there needs to be an explanation as to why it is _impossible_, not just improbable, that a civ would have expanded out into the galaxy and beyond. > [@eburacum\_45](#): > > On the other hand, megastructures such as Dyson Swarms are dynamically unstable, and they will tend to collide with themselves and become orbiting piles of rubble. We might be able to identify them by their unusual composition, but they won’t be in very good shape after a billion years. Only if the civ that created them left them to fend for themselves. Why would they do that? In fact, why would they not expand out, and make a swarm around nearby stars, who then expand to stars further out? > [@Mijin](#): > > I’ve never really liked the idea of Dyson spheres / swarms. It seems weird to me for aliens to use incredible technology and expertise to make…a big wall of parasols. Energy collection to run their civilization, or the computers that they have moved themselves into. > [@echoreply](#): > > So in order to ignore deep time we have to say there are so many alien civilizations, or at least one of them is so large and active, that they are sending probes, radio waves, light, or gravity waves to us essentially continuously, so we don’t miss them. Or just that they don’t _all_ die off, and instead expands. It only takes one. > [@Mangetout](#): > > **Adapt** - be able to use variations in raw materials; be able to exploit different energy resources > and They wouldn’t need to be all that adaptable for that. We know what elements exist and are useful, we know what power sources exist and are useful. That a system has a slightly different chemical composition or different primary wavelength of solar output doesn’t mean that it needs to _evolve_ to those conditions, but rather to use a simple table to determine the best way to use those resources. > [@Mangetout](#): > > **Do something probe-y** - build something to transmit information home, maybe. I see probes not as pure exploration, but as colonization. More of a Bracewell Probe than Voyager. Whether it be uploaded minds, or genetic information with the capability of building bodies at the destination, the point would not be to to transmit information home, but rather to make this star system their new home. > [@Mangetout](#): > > Small, adaptable things will accidentally evolve - through adaptive mechanisms built into them, or through mutation caused by damage; functions can be lost or added. Mutation is a part of life, and it has been since the beginning, otherwise, we’d still be basic cellular structures turning carbon dioxide into methane around sea vents or something. We can design better. We can build in enough redundancy that mutation becomes improbable enough to not be a concern. “Probes” can also be actual civilizations. If we create a self sustaining colony on an asteroid, then that will continue to grow and replicate. At some point, either we will have grown out so far into and past the Oort cloud that we see that we are actually closer to another star than we are to Sol, and/or some colonies decide that this system is getting crowded, and head off to the next star. > [@Grrr](#): > > The idea that we have a basic understanding of the fundamentals of physics seems dubious to me. There is a fair amount that we know. What we _don’t_ know is how much we don’t know. It’s possible that we solve quantum gravity and have a Grand Unified Theory that explains everything in the next decade, but I doubt it. I _suspect_ that there will always be one more layer to the laws of the universe to uncover. > [@Grrr](#): > > And this assumes the human brain is even capable of understanding quantum science in any meaningful way. Depends on what you mean. As it is, the human brain can’t really understand quantum science. At a certain point, analogies and descriptions no longer work, and the only way to “understand” is to do the math. We have long since passed the time when that math was done in our heads, or even on paper, and is now chugging away in supercomputers. But that doesn’t mean that the human mind cannot still be used to solve problems in quantum science. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [May 4, 2021, 2:22pm UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/194 "2021-05-04T14:22:25Z")
> [@k9bfriender](#): > > Energy collection to run their civilization, or the computers that they have moved themselves into. I think you didn’t get my point. It doesn’t matter, it’s just a gut feeling. But I feel that setting up a shell of solar panels feels like an indirect and inefficient way to collect energy. I feel like a civilization able to push around the vast masses involved will have better ways to collect energy from their star. So I’d be surprised if Dyson spheres prove to be a real tech, but it still makes sense to look for them of course. ---
**Author:** ![echoreply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/echoreply/32/3641_2.png) [@echoreply](https://boards.straightdope.com/u/echoreply)\ **Post date:** [May 4, 2021, 2:53pm UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/195 "2021-05-04T14:53:52Z")
> [@Mijin](#): > > **Engineering problems are irrelevant to the Fermi paradox** Unless the engineering problems truly are insurmountable. Interstellar travel is just too difficult and too slow, and after a few million years of trying, space Elon Musk gives up. Each new alien civilization encounters the same engineering problems, perhaps ones we can’t even imagine, and stays stuck in their home system. > [@Mijin](#): > > Not really no. Any civilization just needs to do anything that is detectable to us now. Maybe they are, and we just haven’t detected it. How long has it been since we could detect solar system scale megastructures half way across the galaxy? How much of the galaxy (and others) have we searched for them? There is a large range between “one civilization” and “every rock in space has a civilization”. The frequency just has to be low enough that we don’t intersect. I can’t remember, are you arguing that because nobody on this message board can come up with a satisfying solution to Fermi’s paradox, that means aliens are here, or are we just having a nerd debate about space aliens? (A very worthwhile pass time.) I am not aware of any evidence that strongly suggests space aliens (or their probes or transmissions) have ever visited the earth (though there are lots of _people_ that strongly suggest it, they lack evidence). However, that does not rule out that they exist somewhere, and something as simple as finding an exoplanet with an oxygen rich atmosphere may suggest life exists elsewhere in the universe. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [May 4, 2021, 3:01pm UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/196 "2021-05-04T15:01:29Z")
> [@Mijin](#): > > It doesn’t matter, it’s just a gut feeling. But I feel that setting up a shell of solar panels feels like an indirect and inefficient way to collect energy. I feel like a civilization able to push around the vast masses involved will have better ways to collect energy from their star. I don’t think of it that way. Seems a pretty efficient way, actually. Assuming that we ever develop fusion, it will certainly take more engineering and maintenance than solar panels. Letting the star do the work for you on the first half of the energy generation seems pretty elegant to me. We’ve already started building one. Every solar powered satellite is a component of a Dyson sphere. Assuming that we get off this rock and start building in space, that will only speed up. Maybe we won’t block out 100% of the star’s light, but a pretty significant and detectable fraction of it, absolutely. And if they aren’t doing Dyson swarms, then the next best thing is star lifting, and it seems that would be even easier to spot. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [May 4, 2021, 3:13pm UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/197 "2021-05-04T15:13:46Z")
> [@echoreply](#): > > Each new alien civilization encounters the same engineering problems, perhaps ones we can’t even imagine, and stays stuck in their home system. That’s possible. I was just saying that it’s pointless, in the context of the Fermi paradox, to talk about so-and-so engineering problem. Yes we can speculate that there might be limits on what can be engineered that prevent aliens doing whatever, but the fact that something is incredibly difficult right now for us is completely irrelevant unless it’s literally against the laws of physics. > [@echoreply](#): > > Maybe they are, and we just haven’t detected it. That’s possible. > [@echoreply](#): > > I can’t remember, are you arguing that because nobody on this message board can come up with a satisfying solution to Fermi’s paradox, that means aliens are here, or are we just having a nerd debate about space aliens? (A very worthwhile pass time.) No. I am just keen that people don’t misunderstand the Fermi paradox. This misunderstanding also seems to be a standard Dope pastime. The Fermi paradox is not saying that there are no plausible explanations. There are lots of plausible explanations. The point is, we don’t have enough information yet to know which, if any, of the explanations proposed so far is correct. That shows a fascinating gap in our knowledge right now. Maybe the gap in our knowledge is small – we learn a bit more about abiogenesis and find it’s so ridiculously unlikely that it’s only happened once in our galaxy. Or maybe the gap is big, and there are many aspects of abiogenesis, evolution, sentience, civilization and interstellar transport and communication that form a very complex picture which we will very gradually lift the veil on. Either way, it’s fascinating to speculate on these matters. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [May 4, 2021, 3:24pm UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/198 "2021-05-04T15:24:00Z")
> [@echoreply](#): > > Unless the engineering problems truly are insurmountable. Interstellar travel is just too difficult and too slow, and after a few million years of trying, space Elon Musk gives up. Each new alien civilization encounters the same engineering problems, perhaps ones we can’t even imagine, and stays stuck in their home system. There are always unknowns, but there is nothing known to us to make it insurmountable. If we can build a self sufficient space colony, then we can become interstellar, there really is nothing in between those two. And I see no reason why we cannot build a self sufficient space colony. > [@echoreply](#): > > Maybe they are, and we just haven’t detected it. How long has it been since we could detect solar system scale megastructures half way across the galaxy? Why’s it always gotta be half way? What is the reason that there is such a fine tuning that there is one half way, but not a dozen closer? If there was one within 1400 light years, we can see it. We saw Tabby’s Star, which was fairly close to what we would expect to see if someone was building a solar system scale megastructure. > [@echoreply](#): > > There is a large range between “one civilization” and “every rock in space has a civilization”. The frequency just has to be low enough that we don’t intersect. I just don’t understand what it is that fine tunes it to that specific number. > [@echoreply](#): > > I can’t remember, are you arguing that because nobody on this message board can come up with a satisfying solution to Fermi’s paradox, that means aliens are here, or are we just having a nerd debate about space aliens? You didn’t ask me, I know, but my position is that the two “acceptable” or at least, IMHO, probable, answers to the Fermi Paradox is either that _all_ intelligent species encounter something that kills them off before they are able to expand into an interstellar civ, or that we are the first. I prefer the latter to the former, but I don’t know that we can rule it out. > [@echoreply](#): > > I am not aware of any evidence that strongly suggests space aliens (or their probes or transmissions) have ever visited the earth (though there are lots of _people_ that strongly suggest it, they lack evidence). However, that does not rule out that they exist somewhere, and something as simple as finding an exoplanet with an oxygen rich atmosphere may suggest life exists elsewhere in the universe. I think that we will probably find life all over the place. We have good reason to believe that it existed on Mars, though that needs follow up to confirm, and I think that we will find it on Europa and probably a number of water moons. Intelligent life, however, I think is a whole different story. There is nothing in evolution that favors intelligence, you can’t assume that it is inevitable that a life bearing world would develop it, even given unlimited time. Great filters are either behind us or in front of us. Either there is _no_ intelligent life, or we are it. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [May 4, 2021, 3:42pm UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/199 "2021-05-04T15:42:48Z")
> [@k9bfriender](#): > > There is nothing in evolution that favors intelligence, you can’t assume that it is inevitable that a life bearing world would develop it, even given unlimited time. Well, let’s be precise here, because that line could be misleading. There’s nothing in evolution that favors intelligence _versus other survival traits_ i.e. there are plenty of organisms that are hella successful without needing higher cognitive function, or even a brain. However, intelligence still belongs to the set of survival traits / strategies, so it _is_ favored by evolution in that sense. And while humans are the only extant sentient species, there are plenty of species that have become more intelligent after they branched from our common ancestor; so it isn’t as though getting smarter was only an advantage for us and our direct ancestors. Nothing outside of _Homo_ became sentient of course, but given how quickly sentient species transform their world it seems that any sentient species is likely to find itself the first on its planet. > [@](#): > > Great filters are either behind us or in front of us. Either there is _no_ intelligent life, or we are it. Or there are multiple significant filters below and above us that have a collective effect. ---
**Author:** ![Skywatcher](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/skywatcher/32/254_2.png) [@Skywatcher](https://boards.straightdope.com/u/Skywatcher)\ **Post date:** [May 4, 2021, 3:53pm UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/200 "2021-05-04T15:53:27Z")
> [@digs](#): > > **Are Aliens Visiting Earth?** > > Not if they’re smart. “Why Aliens Don’t Visit Us” – FailArmy [![]( " - YouTube") ](https://www.youtube.com/watch?v=yXKKa26AMVc) ---
**Author:** ![GIGObuster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gigobuster/32/421_2.png) [@GIGObuster](https://boards.straightdope.com/u/GIGObuster)\ **Post date:** [May 4, 2021, 4:03pm UTC](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949/201 "2021-05-04T16:03:08Z")
> [@AlienBabble](#): > > Triangle-shaped UFO vexed UK military in 2016. An unprecedented response to the sighting and the subsequent alleged cover-up: Just saying **AlienBabble** , It is clear others are not replying as it is clear that you ignore previous posts like the one from **eburacum\_45** post #167 [there are better and simple explanations regarding those triangle “UFO”](https://twitter.com/michaelshermer/status/1386160676780101634) [Previous page](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949.md?page=9) [Next page](https://boards.straightdope.com/t/are-aliens-visiting-earth/912949.md?page=11)