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Actually Fermi's paradox makes total sense to me: - Presume that even with something like travel at 1% o speed of light, the Milky Way is colonizable in a coup

by raducu 8y ago

Actually Fermi's paradox makes total sense to me: - Presume that even with something like travel at 1% o speed of light, the Milky Way is colonizable in a couple of million years. - Presume that we are not special at all and there exist more technological advanced civilizations that predate us by at least a couple million years - Presume such a large scale colonization would be easy to observe If you accept the 3 presuppositions, the only logical conclusion is that there are no other technologically advanced species in the Milky Way or that we're the first(very unlikely). Or you can choose to attack any of the presuppositions, but that's also very hard in my humble oppinion.

red75prime 8y ago
P(at least one technologically advanced civilization observes itself | there exists at least one technologically advanced civilization) = 1 We will observe ourselves, no matter how it is unlikely for us to exist. We may not be special, but highly improbable and therefore the first and the only. But such explanation isn't that interesting.
- ubernostrum 8y ago
  You're just stating an anthropic-principle argument here, and unfortunately anthropic arguments tend conceal a fallacy of equivocation. You can look up some of William Lane Craig's work for a formal logical analysis showing exactly where it goes wrong, but the traditional plain-language analogy is: Imagine you're sitting in a prison cell, and you've been told you're going to be executed by a firing squad of a dozen expert marksmen, who will shoot you from a distance of only a few feet away. You're led out of your cell, tied to a stake, the marksmen line up, they raise their rifles and aim at you, and you hear the mass bang of their simultaneous firing. And... you discover you are unharmed. All twelve expert marksmen completely missed you, at close range! The anthropic argument says you should be completely unsurprised; after all, the only way for you to be observing the marksmen now is if they all missed, so the probability of them having missed, given that you are observing them, is 1. We should not be surprised by something which has probability 1. While this is trivially true, it is also utterly unconvincing and utterly pointless. You are perfectly justified in being surprised that all the marksmen missed, and here is the equivocation: the anthropic argument tells you not to be surprised, but the thing it tells you not to be surprised at is not the thing that was actually surprising. Your prior for all the marksmen missing and leaving you completely unharmed should have been very, very low, and no amount of ex-post-facto wrangling can change that. Or, put more simply, anthropic arguments can be used to launder any past event to a probability of 1; after all, the probability of event X having happened, given that you observed event X, is always trivially 1. But it tells you nothing useful whatsoever.
  - acqq 8y ago
    > the probability of them having missed, given that you are observing them, is 1. We should not be surprised by something which has probability 1. While this is trivially true, it is also utterly unconvincing and utterly pointless. It's completely convincing to me. If you are unharmed, no single bullet hit you. Even if you've had the "prior" information like that they are "a firing squad of a dozen expert marksmen" if you are "utterly surprised" by the result it probably means that your priors simply miss something, not that it couldn't have happened at all. E.g. maybe that dozen of experts had some additional decision you didn't know about, e.g. they want to influence a regime change and agreed before that it would start with you not being harmed. Such kind of information turns very improbable event to very probable. More than that, even improbable events do happen all the time. It is very improbable that I personally will never win a huge prize on the lottery ticket, but the lotteries are intentionally made that somebody from time to time wins it. If we are a "lottery winner" and don't know anything about the rules of the lottery and the number of the participants, we just can't conclude anything else about the lottery probabilities than that we got what we got. As long as more different universes are possible, no matter how we think our is improbable, as long as we have information only about our state we don't have to be able to conclude more than that we have what we have. So there's no value is empty talk, we know more only by moving the boundaries of what we can measure. We have actually have learned amazingly much about the Universe, but there's no "guaranteed first prize win" ("learning everything") in these endeavors.
    - deleted 8y ago
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    - ubernostrum 8y ago
      Such kind of information turns very improbable event to very probable. The issue is, as I pointed out, that it works for anything and produces the same result. Anthropic arguments literally consist of stating that "P(A|A) = 1". Which of course is true, but what does that actually tell you?
      - acqq 8y ago
philwelch 8y ago
Why would another species be millions of years ahead of us in development?
- adrianN 8y ago
  Because the universe is pretty old and planets similar to Earth but much older are probably abundant.
- waterhouse 8y ago
  The solar system formed, apparently, 4.6 billion years ago. The universe itself is closer to 14 billion years old. Might a solar system like ours have formed, somewhere, 4.7 billion years ago instead? And once it's formed, how long does it take for life to evolve? If the earth had 10% more surface area, would evolution have occurred 10% faster? There were various huge extinction events during the life of the earth, at least one of which appears to be due to a collision with a giant asteroid; if that happened 70 million years ago instead of 65 million, would humans have evolved a few million years earlier? The point is that, if you rolled the dice on a new universe that had a decent chance of producing something like our Earth, there are lots of sources of variance, such that the "95% confidence interval" during which something like us might have evolved is probably hundreds of millions of years wide. Given that, the chance that two independent civilizations would reach a particular level of technological development during the same million-year period is less than 1%.
- Izkata 8y ago
  Consider how long the dinosaurs were around vs the short period humans existed. If another planet managed to skip over that long delay...
- goatlover 8y ago
  Because planets suitable for life could have formed several billion years before the Earth. Our solar system is relatively recent. I don't know when rocky planets first started to form, but I've heard for at least the past 10 billion years. Also, we don't know what evolution always takes as long to result in a technological species. It could be tens of millions of years slower or faster, just depending.
rdtsc 8y ago
> Milky Way is colonizable in a couple of million years. I have two takes on it: 1) We don't know the possible implication of new discoveries. Well, actually we get some glimpse of it, for example with nuclear or biological weapons around, it is fairly easy to wipe out a large part of the population. The more advanced the technology becomes it seems there is a higher chance of it blowing up in our faces and us destroying ourselves. So the galaxy could be colonizable in a few million years, but any civilization headed closer to that ability, gets closer (and faster) to its own destruction as well. > The only logical conclusion is that there are no other technologically advanced species in the Milky Way or that we're the first(very unlikely). Given my other pessimistic take on it (1), I would say it likely there were (are) quite a few technologically advanced species, but they've wiped themselves out or will do so before the reach the ability to colonize planets in other galaxies. 2) Another take on it is these civilization have to share the same physics and chemistry that we do. And maybe there is just a limit that gets achieved and long term colonization or fast travel is just no possible. That is there are no shortcuts like wormholes, Alcubierre drives, antigravity and other such things. We've been used to seeing huge leaps in technology and science in the last 1000 years, so it's tempting to extrapolate and but maybe we are close to reaching a wall. So there are quite a few civilizations out there but they've flown probes in their own start system, now developed internet and are sharing pictures of alien cats, hanging out on their version of Facebook and watching their alien Netflix, and of course discussing their equivalent of Fermi's Paradox on online forums. All without a chance of ever leaving their neighborhood.
- raducu 8y ago
  1) It takes just ONE civilization not wiping itself out to colonize the galaxy; furthermore, colonizing the galaxy is a great insurance policy against extinction 2) 1% of the speed of light is very achievable even with today's technology, it's just the(irrational) fear of nuclear reactors in space and lack of political will that keeps us from exploring interstellar travel.
  - AstralStorm 8y ago
    We have not implemented space mining that would allow refilling those reactors in space though. Reusable landing is still very iffy.
TheOtherHobbes 8y ago
I suspect your second and third points contradictveach other. We literally have no idea what a >10^6 more advanced civ would look like. There’s a kind of parochialism about these arguments. They seem to assume that aliens will be flying around the galaxy communicating by radio in big metal boxes or giant rocket powered rocks looking for planets to xenoform. But in the same way that ants can’t see a human city around them, it’s possible humans will see no evidence of an advanced civ that isn’t doing any of the things we expect technology to do.
- pavlov 8y ago
  Also, less than 5% of the universe is observable to us. The rest we're calling "dark matter" and "dark energy" because we have no idea what it is. There's a lot we don't know that billion-year-old civilizations may have figured out to use.
- the6threplicant 8y ago
  But that's the beauty of this calculation it just takes one splinter group of one splinter group and they could easily populate the whole galaxy in under 10-100 million years - which, being the conclusion that Fermi found, is nothing at the time scales of when our galaxy was formed.
- Chathamization 8y ago
  > We literally have no idea what a >10^6 more advanced civ would look like. Yep. We don't even have much of a clue about what our own civilization will look like a few hundred years from now, it seems insane to pretend we would know what a far more advanced alien civilization would look like. Imagine showing someone from a thousand years ago a picture of suburbia and them saying, "Nope, this place must be abandoned...no one is growing crops on the land, there are no wells around, deer and other wildlife are walking around houses without being hunted. Must be no humans there." Even just a few decades ago a lot of people thought we would be building cities under the seas by now (hey, maybe not everyone would do it - but with billions of humans, it would only take a few splinter groups). It's also worth pointing out that even a civilization at our level existing at the nearest star would be undetectable to us in most circumstances (even in the extremely unlikely event that the timing matched up).
dingaling 8y ago
The third premise is its downfall, though. A WW1 wireless operator of only 100 years ago wouldn't be able to detect modern spread-spectrum military radios, let alone separate encrypted signals from the noise. Why should we suppose we could detect a civilisation two million years more advanced?
- bodas 8y ago
  I think the point is that they would have colonised Earth already. It is comparing the age of the Earth (billions of years) to the size of the galaxy (100kly)
  - vidarh 8y ago
    Or maybe the value of colonising a planet relative to the cost just does't make it worth it by the time you have the technology to try. Maybe every advanced civilisation ends up turning inwards to simulations rather than outwards. Maybe there are aliens all around us, but we can't notice them, because we're living in someones phone, in the latest top-hit: SimHumans5000. There's quite literally an infinite number of possibilities where we're not alone after all, and part of the problem is that we don't just not know the values to plug into the relevant probability calculations, but we don't even know all the variables.
    - raducu 8y ago
      An inwards turning civilization would be much more incentivised to collect all the matter they can since E=mc^2, and for them E is their lifespan. For a civilization living for trillions upon trilions of years inside a simulation, intergalactic latancy is just a blink of an eye -- they have no reason not to distribute their simulation across the galaxy. All of the burning stars would be just lost time for such a civilization
  - jsjohnst 8y ago
    > I think the point is that they would have colonised Earth already. Not saying I believe this, but are we sure they haven’t? There’s a bunch of fringe people who believe it did happen.
skgoa 8y ago
This is not hard to attack: > Presume such a large scale colonization would be easy to observe There is no reason why this should be true.
Mirioron 8y ago
>the only logical conclusion is that there are no other technologically advanced species in the Milky Way or that we're the first(very unlikely). Why is this unlikely? The likelihood of intelligent life emerging that gets far enough in their development to try to colonize a galaxy might be so low that it could easily only be once per galaxy or even rarer than that. Think about how long multicellular life has existed on this planet and yet a very narrow band ended up 'becoming intelligent' and even then it took a long time before industrialization that finally propelled us forward.
krapp 8y ago
> Presume that even with something like travel at 1% o speed of light, the Milky Way is colonizable in a couple of million years. You're not assuming that it is, you're assuming that if it can be, it must be. Which assumes that every part of the milky way is equally amenable to colonization, as if the galaxy were merely points laid out on a Cartesian grid, and that any species capable of colonizing one star must continue to colonize them all. You must consider the case of technologically advanced species incapable of colonizing other stars, and technologically advanced species capable of colonizing other stars, but unwilling to do so on a large scale, or attempts at large scale colonization which fail across a scale of millions of years or even attempts to hide the obvious presence of such colonization from observers. >Presume that we are not special at all and there exist more technological advanced civilizations that predate us by at least a couple million years Ok. >Presume such a large scale colonization would be easy to observe By humans, given that we only recently became aware that extrasolar planets are even a thing, and have only been studying the universe with anything but optical telescopes for less than a century, and don't even know what the signs of "large scale colonization" would look like. No. Why? >Or you can choose to attack any of the presuppositions, but that's also very hard in my humble oppinion. Any argument can seem airtight when you refuse to consider more than a single case to be valid.
- goatlover 8y ago
  But it only takes one advanced civilization to do it. And we're probably only a century away from being able to spam the entire galaxy with probes, if we wanted to say take apart Mercury and use solar panels for propulsion. The probes would be small, smart and able to replicate themselves.
  - vkou 8y ago
    > And we're probably only a century away from being able to spam the entire galaxy with probes, if we wanted to say take apart Mercury and use solar panels for propulsion. The probes would be small, smart and able to replicate themselves. 1. We're really not. 2. Solar panels obey the inverse square law. Right now, we can't even use solar panels to power probes beyond the orbit of Jupiter - let alone drive an energy-hungry ion engine. 3. Even with an ion engine, you need fuel to thrust. 4. Even if we could send them, they'd need incredibly power-hungry antennas to transmit any useful data back. See 2. People say things like 'only 1% of c' as if it's trivial. It's only 1%! It's also 3,000 km/s. No man-made machine has ever gone faster then 16 km/s. If we tried really hard, we might hit 1% of 1% of C. And then it would still take that probe 400 years to visit our nearest star. 10 million years to cross the galaxy.
AnIdiotOnTheNet 8y ago
If you have the ability to live in space long enough to cover the vast distances between stars, why would you bother colonizing planets at all? Pretty much all the raw material you need is readily available in asteroids without having to deal with a steep gravity well or a thick atmosphere, and the star itself will give you plenty of energy to work with. Pretty much every star system becomes habitable if you don't have to care about whether or not it has a planet that meets your species's environmental needs.
- bluGill 8y ago
  Only if gravity isn't a requirement of life. We know that bad things happen to humans when in low/zero-g for more than a month. What happens to when we are talking about lifetimes - science is exploring this topic but doesn't really have answers.
  - gnode 8y ago
    > We know that bad things happen to humans when in low/zero-g for more than a month. This is mainly because humans are adapted to live standing upright in gravitational conditions, with a pressure gradient across their body. If you take animals which are not adapted for this (e.g. large invertebrates from the sea) they're crushed by their own weight when taken out of a buoyant environment. Even so, that doesn't make it infeasible to live in space for long periods of time. Artificial gravity can be generated with a centrifuge. However, I would say it's likely that gravity is necessary for life similar to what we are familiar with to form in the first place. Earth's gravity facilitates the existence of dense fluids, allowing for the complex reactions of primordial life.
  - magduf 8y ago
    A civilization advanced enough to colonize other star systems likely 1) is advanced enough to tweak their genetics to deal with low/zero gravity 2) is advanced enough to build a ship with artificial gravity (we came up with this idea long ago, go watch "2001", it's not hard).
- raducu 8y ago
jonathanstrange 8y ago
- There is no reason to believe that species want to colonize the whole Milky Way. In fact, our current value and belief systems would not recommend such an expansion either. (The same for self-multiplying robot ships - if you think it's a bad idea, why would aliens think otherwise?) - Cyclical cultures, filters, and large time frames are not properly taken into account. If you take them into account, colonization of the whole Milky Way seems unlikely. - Life could occur only very rarely. So basically, the missing premise is that if all of your conditions are fulfilled, then a civilization will colonize the Milky Way and has done so far enough in the past that we can easily observe it. There is no reason to think that. Now here is the bad news: Even if we accept your original line of thought, that would still be entirely compatible with the view that some intelligent species is just about to colonize the Milky Way and just in front of our doorstep... I'm just kidding, of course. Like others have pointed out, this "research" is almost entirely based on speculation. We don't even know how likely life would arise if all conditions for life are fulfilled, let alone whether that also means that intelligent life will arise or with which likelihood. We know nothing. The only thing that we can say with relative certainty according to our current knowledge is that if intelligent life develops with high probability whenever the conditions for life are met, then it is a bit harder to detect then we thought or Xenoarchaeology will be booming some day in the future.
- aeorgnoieang 8y ago
  > In fact, our current value and belief systems would not recommend such an expansion either. This just isn't true. There are current value and belief systems, even ones held by people with a relative large amount of political and economic power, that do in fact recommend such an expansion (someday).
  - DennisP 8y ago
    I would say it's the dominant value system, given that our global economy and energy consumption grows by around 2% per year, with no serious efforts to change that.
    - 8y ago
posterboy 8y ago
> Presume that even with something like travel at 1% o speed of light, the Milky Way is colonizable in a couple of million years Imagine an intergalactic astro physicist raising three eye brows, wondering, "only?!"
naravara 8y ago
>If you accept the 3 presuppositions, the only logical conclusion is that there are no other technologically advanced species in the Milky Way or that we're the first(very unlikely). Or they have a culture/value system that doesn't care about sprawling out to occupy as much space as possible. Why is it presumed that advanced alien civilizations would use their technology to maximize, rather than minimize their ecological footprint? It stands to reason that environmental degradation could be one of the major filtering mechanisms for advanced life and any civilization that clears the filter will need to have fostered sustainable, symbiotic production systems rather than extractive ones.
- KaoruAoiShiho 8y ago
  Game theory basically. Any civilizations that minimizes would be destroyed by any civ that maximizes, so the survivors must be maximizers. Furthermore any civ that minimizes would never get to an advanced stage in the first place.
  - naravara 8y ago
    >Any civilizations that minimizes would be destroyed by any civ that maximizes Unless we're talking about hive-minds I don't think this premise holds at all. Civilizations that culturally value domination and expansion can dominate within their own civilization much more easily than casting out into space to find alien ones. They're more likely to destroy themselves than others.
Freestyler_3 8y ago
More technical advanced meaning they can effectively use all resources on their own planet? Or even further where they can effectively gather all the energy from their star? The only reasons to branch out is because your own star is dying or your population (demand for energy) is growing too fast. Essentially I think that population control is a big hurdle for any advanced species. Which would be the main drive for colonizing space. But at what rate does it grow? After their first star, how long does it take for the next one to be used fully.
- raducu 8y ago
  Or they would gather all the mass they can before the heat death of the universe, since E=mc^2 and since they could live forever.
Semirhage 8y ago
Why would a species want to colonize a galaxy? You’re talking about insane travel and communication times after all, and spreading very thin. Sticking to a single system or handful of systems while controlling reproduction rates is a solution that achieves the same ends without spreading your species so far that it amounts to a million different civilizations. At some point over such distances you’re not colonizing anything, just throwing generations into the night with no hope of a return. That same energy could be used to engineer a structure or structured for those same beings to live within a reasonable distance of each other. The whole Fermi Paradox reasoning is flawed, because the assumptions are flawed.

by raducu 8y ago

red75prime 8y ago

P(at least one technologically advanced civilization observes itself | there exists at least one technologically advanced civilization) = 1 We will observe ourselves, no matter how it is unlikely for us to exist. We may not be special, but highly improbable and therefore the first and the only. But such explanation isn't that interesting.

ubernostrum 8y ago
You're just stating an anthropic-principle argument here, and unfortunately anthropic arguments tend conceal a fallacy of equivocation. You can look up some of William Lane Craig's work for a formal logical analysis showing exactly where it goes wrong, but the traditional plain-language analogy is: Imagine you're sitting in a prison cell, and you've been told you're going to be executed by a firing squad of a dozen expert marksmen, who will shoot you from a distance of only a few feet away. You're led out of your cell, tied to a stake, the marksmen line up, they raise their rifles and aim at you, and you hear the mass bang of their simultaneous firing. And... you discover you are unharmed. All twelve expert marksmen completely missed you, at close range! The anthropic argument says you should be completely unsurprised; after all, the only way for you to be observing the marksmen now is if they all missed, so the probability of them having missed, given that you are observing them, is 1. We should not be surprised by something which has probability 1. While this is trivially true, it is also utterly unconvincing and utterly pointless. You are perfectly justified in being surprised that all the marksmen missed, and here is the equivocation: the anthropic argument tells you not to be surprised, but the thing it tells you not to be surprised at is not the thing that was actually surprising. Your prior for all the marksmen missing and leaving you completely unharmed should have been very, very low, and no amount of ex-post-facto wrangling can change that. Or, put more simply, anthropic arguments can be used to launder any past event to a probability of 1; after all, the probability of event X having happened, given that you observed event X, is always trivially 1. But it tells you nothing useful whatsoever.
- acqq 8y ago
  > the probability of them having missed, given that you are observing them, is 1. We should not be surprised by something which has probability 1. While this is trivially true, it is also utterly unconvincing and utterly pointless. It's completely convincing to me. If you are unharmed, no single bullet hit you. Even if you've had the "prior" information like that they are "a firing squad of a dozen expert marksmen" if you are "utterly surprised" by the result it probably means that your priors simply miss something, not that it couldn't have happened at all. E.g. maybe that dozen of experts had some additional decision you didn't know about, e.g. they want to influence a regime change and agreed before that it would start with you not being harmed. Such kind of information turns very improbable event to very probable. More than that, even improbable events do happen all the time. It is very improbable that I personally will never win a huge prize on the lottery ticket, but the lotteries are intentionally made that somebody from time to time wins it. If we are a "lottery winner" and don't know anything about the rules of the lottery and the number of the participants, we just can't conclude anything else about the lottery probabilities than that we got what we got. As long as more different universes are possible, no matter how we think our is improbable, as long as we have information only about our state we don't have to be able to conclude more than that we have what we have. So there's no value is empty talk, we know more only by moving the boundaries of what we can measure. We have actually have learned amazingly much about the Universe, but there's no "guaranteed first prize win" ("learning everything") in these endeavors.
  - deleted 8y ago
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  - ubernostrum 8y ago
    Such kind of information turns very improbable event to very probable. The issue is, as I pointed out, that it works for anything and produces the same result. Anthropic arguments literally consist of stating that "P(A|A) = 1". Which of course is true, but what does that actually tell you?
    - acqq 8y ago

philwelch 8y ago

Why would another species be millions of years ahead of us in development?

adrianN 8y ago
Because the universe is pretty old and planets similar to Earth but much older are probably abundant.
waterhouse 8y ago
The solar system formed, apparently, 4.6 billion years ago. The universe itself is closer to 14 billion years old. Might a solar system like ours have formed, somewhere, 4.7 billion years ago instead? And once it's formed, how long does it take for life to evolve? If the earth had 10% more surface area, would evolution have occurred 10% faster? There were various huge extinction events during the life of the earth, at least one of which appears to be due to a collision with a giant asteroid; if that happened 70 million years ago instead of 65 million, would humans have evolved a few million years earlier? The point is that, if you rolled the dice on a new universe that had a decent chance of producing something like our Earth, there are lots of sources of variance, such that the "95% confidence interval" during which something like us might have evolved is probably hundreds of millions of years wide. Given that, the chance that two independent civilizations would reach a particular level of technological development during the same million-year period is less than 1%.
Izkata 8y ago
Consider how long the dinosaurs were around vs the short period humans existed. If another planet managed to skip over that long delay...
goatlover 8y ago
Because planets suitable for life could have formed several billion years before the Earth. Our solar system is relatively recent. I don't know when rocky planets first started to form, but I've heard for at least the past 10 billion years. Also, we don't know what evolution always takes as long to result in a technological species. It could be tens of millions of years slower or faster, just depending.

rdtsc 8y ago

> Milky Way is colonizable in a couple of million years. I have two takes on it: 1) We don't know the possible implication of new discoveries. Well, actually we get some glimpse of it, for example with nuclear or biological weapons around, it is fairly easy to wipe out a large part of the population. The more advanced the technology becomes it seems there is a higher chance of it blowing up in our faces and us destroying ourselves. So the galaxy could be colonizable in a few million years, but any civilization headed closer to that ability, gets closer (and faster) to its own destruction as well. > The only logical conclusion is that there are no other technologically advanced species in the Milky Way or that we're the first(very unlikely). Given my other pessimistic take on it (1), I would say it likely there were (are) quite a few technologically advanced species, but they've wiped themselves out or will do so before the reach the ability to colonize planets in other galaxies. 2) Another take on it is these civilization have to share the same physics and chemistry that we do. And maybe there is just a limit that gets achieved and long term colonization or fast travel is just no possible. That is there are no shortcuts like wormholes, Alcubierre drives, antigravity and other such things. We've been used to seeing huge leaps in technology and science in the last 1000 years, so it's tempting to extrapolate and but maybe we are close to reaching a wall. So there are quite a few civilizations out there but they've flown probes in their own start system, now developed internet and are sharing pictures of alien cats, hanging out on their version of Facebook and watching their alien Netflix, and of course discussing their equivalent of Fermi's Paradox on online forums. All without a chance of ever leaving their neighborhood.

raducu 8y ago
1) It takes just ONE civilization not wiping itself out to colonize the galaxy; furthermore, colonizing the galaxy is a great insurance policy against extinction 2) 1% of the speed of light is very achievable even with today's technology, it's just the(irrational) fear of nuclear reactors in space and lack of political will that keeps us from exploring interstellar travel.
- AstralStorm 8y ago
  We have not implemented space mining that would allow refilling those reactors in space though. Reusable landing is still very iffy.

TheOtherHobbes 8y ago

I suspect your second and third points contradictveach other. We literally have no idea what a >10^6 more advanced civ would look like. There’s a kind of parochialism about these arguments. They seem to assume that aliens will be flying around the galaxy communicating by radio in big metal boxes or giant rocket powered rocks looking for planets to xenoform. But in the same way that ants can’t see a human city around them, it’s possible humans will see no evidence of an advanced civ that isn’t doing any of the things we expect technology to do.

pavlov 8y ago
Also, less than 5% of the universe is observable to us. The rest we're calling "dark matter" and "dark energy" because we have no idea what it is. There's a lot we don't know that billion-year-old civilizations may have figured out to use.
the6threplicant 8y ago
But that's the beauty of this calculation it just takes one splinter group of one splinter group and they could easily populate the whole galaxy in under 10-100 million years - which, being the conclusion that Fermi found, is nothing at the time scales of when our galaxy was formed.
Chathamization 8y ago
> We literally have no idea what a >10^6 more advanced civ would look like. Yep. We don't even have much of a clue about what our own civilization will look like a few hundred years from now, it seems insane to pretend we would know what a far more advanced alien civilization would look like. Imagine showing someone from a thousand years ago a picture of suburbia and them saying, "Nope, this place must be abandoned...no one is growing crops on the land, there are no wells around, deer and other wildlife are walking around houses without being hunted. Must be no humans there." Even just a few decades ago a lot of people thought we would be building cities under the seas by now (hey, maybe not everyone would do it - but with billions of humans, it would only take a few splinter groups). It's also worth pointing out that even a civilization at our level existing at the nearest star would be undetectable to us in most circumstances (even in the extremely unlikely event that the timing matched up).

dingaling 8y ago

The third premise is its downfall, though. A WW1 wireless operator of only 100 years ago wouldn't be able to detect modern spread-spectrum military radios, let alone separate encrypted signals from the noise. Why should we suppose we could detect a civilisation two million years more advanced?

bodas 8y ago
I think the point is that they would have colonised Earth already. It is comparing the age of the Earth (billions of years) to the size of the galaxy (100kly)
- vidarh 8y ago
  Or maybe the value of colonising a planet relative to the cost just does't make it worth it by the time you have the technology to try. Maybe every advanced civilisation ends up turning inwards to simulations rather than outwards. Maybe there are aliens all around us, but we can't notice them, because we're living in someones phone, in the latest top-hit: SimHumans5000. There's quite literally an infinite number of possibilities where we're not alone after all, and part of the problem is that we don't just not know the values to plug into the relevant probability calculations, but we don't even know all the variables.
  - raducu 8y ago
    An inwards turning civilization would be much more incentivised to collect all the matter they can since E=mc^2, and for them E is their lifespan. For a civilization living for trillions upon trilions of years inside a simulation, intergalactic latancy is just a blink of an eye -- they have no reason not to distribute their simulation across the galaxy. All of the burning stars would be just lost time for such a civilization
- jsjohnst 8y ago
  > I think the point is that they would have colonised Earth already. Not saying I believe this, but are we sure they haven’t? There’s a bunch of fringe people who believe it did happen.

skgoa 8y ago

This is not hard to attack: > Presume such a large scale colonization would be easy to observe There is no reason why this should be true.

Mirioron 8y ago

>the only logical conclusion is that there are no other technologically advanced species in the Milky Way or that we're the first(very unlikely). Why is this unlikely? The likelihood of intelligent life emerging that gets far enough in their development to try to colonize a galaxy might be so low that it could easily only be once per galaxy or even rarer than that. Think about how long multicellular life has existed on this planet and yet a very narrow band ended up 'becoming intelligent' and even then it took a long time before industrialization that finally propelled us forward.

krapp 8y ago

> Presume that even with something like travel at 1% o speed of light, the Milky Way is colonizable in a couple of million years. You're not assuming that it is, you're assuming that if it can be, it must be. Which assumes that every part of the milky way is equally amenable to colonization, as if the galaxy were merely points laid out on a Cartesian grid, and that any species capable of colonizing one star must continue to colonize them all. You must consider the case of technologically advanced species incapable of colonizing other stars, and technologically advanced species capable of colonizing other stars, but unwilling to do so on a large scale, or attempts at large scale colonization which fail across a scale of millions of years or even attempts to hide the obvious presence of such colonization from observers. >Presume that we are not special at all and there exist more technological advanced civilizations that predate us by at least a couple million years Ok. >Presume such a large scale colonization would be easy to observe By humans, given that we only recently became aware that extrasolar planets are even a thing, and have only been studying the universe with anything but optical telescopes for less than a century, and don't even know what the signs of "large scale colonization" would look like. No. Why? >Or you can choose to attack any of the presuppositions, but that's also very hard in my humble oppinion. Any argument can seem airtight when you refuse to consider more than a single case to be valid.

goatlover 8y ago
But it only takes one advanced civilization to do it. And we're probably only a century away from being able to spam the entire galaxy with probes, if we wanted to say take apart Mercury and use solar panels for propulsion. The probes would be small, smart and able to replicate themselves.
- vkou 8y ago
  > And we're probably only a century away from being able to spam the entire galaxy with probes, if we wanted to say take apart Mercury and use solar panels for propulsion. The probes would be small, smart and able to replicate themselves. 1. We're really not. 2. Solar panels obey the inverse square law. Right now, we can't even use solar panels to power probes beyond the orbit of Jupiter - let alone drive an energy-hungry ion engine. 3. Even with an ion engine, you need fuel to thrust. 4. Even if we could send them, they'd need incredibly power-hungry antennas to transmit any useful data back. See 2. People say things like 'only 1% of c' as if it's trivial. It's only 1%! It's also 3,000 km/s. No man-made machine has ever gone faster then 16 km/s. If we tried really hard, we might hit 1% of 1% of C. And then it would still take that probe 400 years to visit our nearest star. 10 million years to cross the galaxy.

AnIdiotOnTheNet 8y ago

If you have the ability to live in space long enough to cover the vast distances between stars, why would you bother colonizing planets at all? Pretty much all the raw material you need is readily available in asteroids without having to deal with a steep gravity well or a thick atmosphere, and the star itself will give you plenty of energy to work with. Pretty much every star system becomes habitable if you don't have to care about whether or not it has a planet that meets your species's environmental needs.

bluGill 8y ago
Only if gravity isn't a requirement of life. We know that bad things happen to humans when in low/zero-g for more than a month. What happens to when we are talking about lifetimes - science is exploring this topic but doesn't really have answers.
- gnode 8y ago
  > We know that bad things happen to humans when in low/zero-g for more than a month. This is mainly because humans are adapted to live standing upright in gravitational conditions, with a pressure gradient across their body. If you take animals which are not adapted for this (e.g. large invertebrates from the sea) they're crushed by their own weight when taken out of a buoyant environment. Even so, that doesn't make it infeasible to live in space for long periods of time. Artificial gravity can be generated with a centrifuge. However, I would say it's likely that gravity is necessary for life similar to what we are familiar with to form in the first place. Earth's gravity facilitates the existence of dense fluids, allowing for the complex reactions of primordial life.
- magduf 8y ago
  A civilization advanced enough to colonize other star systems likely 1) is advanced enough to tweak their genetics to deal with low/zero gravity 2) is advanced enough to build a ship with artificial gravity (we came up with this idea long ago, go watch "2001", it's not hard).
raducu 8y ago

jonathanstrange 8y ago

- There is no reason to believe that species want to colonize the whole Milky Way. In fact, our current value and belief systems would not recommend such an expansion either. (The same for self-multiplying robot ships - if you think it's a bad idea, why would aliens think otherwise?) - Cyclical cultures, filters, and large time frames are not properly taken into account. If you take them into account, colonization of the whole Milky Way seems unlikely. - Life could occur only very rarely. So basically, the missing premise is that if all of your conditions are fulfilled, then a civilization will colonize the Milky Way and has done so far enough in the past that we can easily observe it. There is no reason to think that. Now here is the bad news: Even if we accept your original line of thought, that would still be entirely compatible with the view that some intelligent species is just about to colonize the Milky Way and just in front of our doorstep... I'm just kidding, of course. Like others have pointed out, this "research" is almost entirely based on speculation. We don't even know how likely life would arise if all conditions for life are fulfilled, let alone whether that also means that intelligent life will arise or with which likelihood. We know nothing. The only thing that we can say with relative certainty according to our current knowledge is that if intelligent life develops with high probability whenever the conditions for life are met, then it is a bit harder to detect then we thought or Xenoarchaeology will be booming some day in the future.

aeorgnoieang 8y ago
> In fact, our current value and belief systems would not recommend such an expansion either. This just isn't true. There are current value and belief systems, even ones held by people with a relative large amount of political and economic power, that do in fact recommend such an expansion (someday).
- DennisP 8y ago
  I would say it's the dominant value system, given that our global economy and energy consumption grows by around 2% per year, with no serious efforts to change that.
  - 8y ago

posterboy 8y ago

> Presume that even with something like travel at 1% o speed of light, the Milky Way is colonizable in a couple of million years Imagine an intergalactic astro physicist raising three eye brows, wondering, "only?!"

naravara 8y ago

>If you accept the 3 presuppositions, the only logical conclusion is that there are no other technologically advanced species in the Milky Way or that we're the first(very unlikely). Or they have a culture/value system that doesn't care about sprawling out to occupy as much space as possible. Why is it presumed that advanced alien civilizations would use their technology to maximize, rather than minimize their ecological footprint? It stands to reason that environmental degradation could be one of the major filtering mechanisms for advanced life and any civilization that clears the filter will need to have fostered sustainable, symbiotic production systems rather than extractive ones.

KaoruAoiShiho 8y ago
Game theory basically. Any civilizations that minimizes would be destroyed by any civ that maximizes, so the survivors must be maximizers. Furthermore any civ that minimizes would never get to an advanced stage in the first place.
- naravara 8y ago
  >Any civilizations that minimizes would be destroyed by any civ that maximizes Unless we're talking about hive-minds I don't think this premise holds at all. Civilizations that culturally value domination and expansion can dominate within their own civilization much more easily than casting out into space to find alien ones. They're more likely to destroy themselves than others.

Freestyler_3 8y ago

More technical advanced meaning they can effectively use all resources on their own planet? Or even further where they can effectively gather all the energy from their star? The only reasons to branch out is because your own star is dying or your population (demand for energy) is growing too fast. Essentially I think that population control is a big hurdle for any advanced species. Which would be the main drive for colonizing space. But at what rate does it grow? After their first star, how long does it take for the next one to be used fully.

raducu 8y ago
Or they would gather all the mass they can before the heat death of the universe, since E=mc^2 and since they could live forever.

Semirhage 8y ago

Why would a species want to colonize a galaxy? You’re talking about insane travel and communication times after all, and spreading very thin. Sticking to a single system or handful of systems while controlling reproduction rates is a solution that achieves the same ends without spreading your species so far that it amounts to a million different civilizations. At some point over such distances you’re not colonizing anything, just throwing generations into the night with no hope of a return. That same energy could be used to engineer a structure or structured for those same beings to live within a reasonable distance of each other. The whole Fermi Paradox reasoning is flawed, because the assumptions are flawed.