24 ms·

The Big Alien Theory

147 points by lisper 5y ago

hindsightbias 5y ago
Decades back, Omni Magazine talked to biologists about what dinosaurs could have evolved to if it hadn't been for the meteor. They seemed to have assumed the smart ones would have all been human sized.
- 867-5309 5y ago
  other than birds, crocodilians, etc.
- cletus 5y ago
  So the thing about the dinosaurs is they were probably always doomed. It just happened to be the meteor that (mostly) finished them off. Why? Well, in times of consistency, the natural trend is for life to get bigger. For herbivores, bigger means access to more vegetation (eg giraffes can eat higher in trees) and is a defense against predators. For predators, size increases the size of prey you can, well, prey on. But as soon as there's a sudden change, size is a disadvantage. You have high food needs (predator or prey). This makes you vulnerable. It's probably more amazing that the dinosaur era lasted >150M years than that this era was ended by a meteor impact.
  - booleandilemma 5y ago
    It’s crazy that they lasted > 150M years and never developed intelligence. Meanwhile we’ve been here just 10 million years or so and we’re starting to make it to other planets.
    - nojokes 5y ago
      Perhaps they did but they did not have means to express themselves and modify the environment?
      - booleandilemma 5y ago
        I started thinking about that after I posted. What a shame that would be!
      - nullc 5y ago
        https://pbfcomics.com/comics/dinosaur-meteors/ https://pbfcomics.com/comics/dinosaur-meteors/
    - deleted 5y ago
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    - asdff 5y ago
      Intelligence is usually a huge waste of resources so it's not typically selected for past a certain level. I would still consider my cat highly intelligent with her strategy making during play, and her understanding of human emotions. In the case of our ancestors, there was a time when traditional resource gathering techniques were not as successful as those that took strategy, coordination with others, understanding migrations of other animals and seasonal progressions of edible plants, and potentially even tool use. Those that were intelligent enough to adopt these techniques managed to feed themselves and reproduce, while those lineages that weren't struggled, and eventually died out entirely. The end of the Neanderthal was sort of like this. They failed to improve their hunting strategies, their population shrank especially in competition with early humans, and eventually they died out.
    - cpeterso 5y ago
      Or dinosaurs developed technology, detected the killer meteor, and relocated to Venus.
    - edgyquant 5y ago
      Mammals have been around for more than a hundred million years, maybe as old as the first dinosaurs themselves. 10 million years is about the time humans and gorillas diverged from a common ancestor. We’ve been evolving just as long as every other animal and it was environmental pressures (and luck) that lead to us being what we are.
  - majkinetor 5y ago
    Whales seem to have better feeding strategy as they can depend on microbiota.
  - sgt101 5y ago
    There were small dinosaurs as well...
    - acjohnson55 5y ago
      Some of them still exist! https://en.wikipedia.org/wiki/Origin_of_birds https://en.wikipedia.org/wiki/Origin_of_birds
      - cletus 5y ago
        That's kind of the point: the _small_ ones still exist.
        Jorengarenar 5y ago
        And some are crazy intelligent
  - catlifeonmars 5y ago
    There were plenty of small dinosaurs.
- asdff 5y ago
  More large (potentially far more terrifying )flightless birds today, that's probably it.
bryanrasmussen 5y ago
>We cannot learn anything about aliens until we find them" >The above statement might sound reasonable, and intuitive, but it lacks justification. Standing on its own, it’s just a piece of dogma. well let's try the following statement then 1. Most things that are learned about are observed to exist before being studied. There are rare items of knowledge that are cogitated upon first and found to exist later, but in general things that you learn about will be like most of the things that you learn about - they will be observed as existing and then be studied.
- dwohnitmok 5y ago
  > Most things that are learned about are observed to exist before being studied. Is this true at this point for physics and astronomy? I have no idea what the relative proportion of discoveries are "this was predicted to exist and we found it!" vs "whoa this is totally unexpected." I suspect that there's also a ton of things in the middle, where an anomalous reading that doesn't directly show the existence of something but does show the deficiency of a theory then leads to corrections in the theory which then result in another cascade of predictions of existence from the theory.
- sorokod 5y ago
  A lot of math is done by working on conjectures that take time to prove or disprove.
  - phkahler 5y ago
    Conjectures in math are based on observations and intuition gained from related observable things. Specifically they seem to be statements about properties of things already known.
    - sorokod 5y ago
      Allowing the word "related" to do a lot of heavy lifting, I'd say that it is the same for aliens.
    - neonological 5y ago
bostonsre 5y ago
If larger aliens means smaller populations of aliens, would that mean that there are fewer possibilities for einsteins to come into existence? If einsteins are less likely, I could see the rate of growth of civilizations being slower, but no real intuition of whether or not that would make much of a difference in the long term.
- thisiscorrect 5y ago
  Does this assume that the likelihood of each alien to be an "einstein" remains constant with size? It seems like a larger being which can support a larger brain might stand a better chance to develop higher thoughts.
  - teruakohatu 5y ago
    Larger brains don't necessarily mean higher cognitive function. Humans have smaller brains than African elephants and many dolphin and whale species.
    - fighterpilot 5y ago
      "Necessarily" is a standard that's too strict and binary. The relevant question is to what extent brain size facilitates and is correlated with intelligence. It doesn't seem to be irrelevant. Large brains are correlated with higher IQ within humans. Also, humans' intelligence came about with an almost doubling in brain volume over two million years. Across very different species there is a weaker correlation but it still seems to be positive. Whales and dolphins are far smarter than ants. Octopuses seem to be an outlier in that respect. I think it's fair to say that the probability of an "Einstein" is positively correlated with body mass, and therefore negatively correlated with population density, at least up to a point (whether that correlation turns negative beyond a point can be debated).
      - baja_blast 5y ago
        Bird brains, such as parrot and crows so that brain size is not everything. A crows brain is smaller than a chimps in overall size and body:brain ratio, yet crows show more complex social behavior, problem solving and tool use (despite not having hands). Bird's brains are much denser than mammals, so it's less size and more number of neurons, and the complexity of how these neurons are networked.
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Semiapies 5y ago
At some point, this sort of thing turns into a weird inverse of naive copernicanism. I look forward to the version of this argument that concludes that we statistically must be the giant aliens and everyone else in the universe is probably hobbit-sized. ETA: or the copernican wrap-around: "Any random person is more likely to be near an average size than not, so...[five dubious steps later]...obviously aliens are mostly going to be average human-sized."
- shakezula 5y ago
  I take this the same way I take the Drake equations: As an interesting thought experiment but only as good as the assumptions they make. But I will say this is based on entirely reasonable assumptions and observations. It's an interesting argument as I've always been of the opinion that life is abundant but the universe so large that it's still quite spread out.
  - mortenjorck 5y ago
    > I've always been of the opinion that life is abundant but the universe so large that it's still quite spread out. This is basically my optimistic/pessimistic view of alien life. The scale of the universe means the probability of alien life existing must be essentially 100%, while the scale of the universe also means the probability of any life finding another instance of life must be essentially 0%. Although a fun corollary inspired by the Big Alien thought experiment is that local maxima must also exist: Somewhere, some planet with intelligent life must have been close enough to another such planet that they did indeed find each other.
    - shakezula 5y ago
      > local maxima must also exist Interesting point. It follows that as we can observe how galaxies and clusters form, it must follow that if life requires a star, it would cluster and group similarly, and eventually group closely enough for two intelligent species to bump into one another.
      - 5y ago
cletus 5y ago
I'm usually a skeptic but I don't buy into the idea that we can't reason anything about aliens until we find them. Some things are just physics. Physics places absolute limits on how small or large an organism can be, for example. It's why I'm not worried about the possibility of superintelligent viruses. There is a long theory of the value of thought experiments in science. The word "atom" is derived from the Greek "atomos", which was the result of a 2000+ year old thought experiment about if something was infinitely divisible or not. Experimental evidence didn't come until the 1800s (IIRC). It seems weird that any article talking about possible alien life doesn't at least touch on the anthropic principle, which is a whole set of thought experiments. My personal view is that our knowledge of the Universe at this point isn't perfect but it's closer to correct than not. That means (IMHO) the speed of light is an absolute limit and thermodynamics holds true. With just those two things, you have a lot of constraints and you can start making some observations. For example: a burgeoning civilization needs energy (and matter), will produce waste heat and that waste heat has to go somewhere. This of course touches on various thought experiments relating to the Fermi Paradox. My personal view is that there simply aren't any starfaring civilizations to find within a pretty large (1M+ light years) light cone. And if you look at the Milky Way, if there aren't any to find now, it's highly unlikely there other civilizations beyond our light cone just because of the low probability of two (or more) such civilizations evolving to that point within 100,000 years of each other.
- colordrops 5y ago
  > superintelligent viruses What if some virus evolved to work super intelligently as a hive mind? > My personal view is that our knowledge of the Universe at this point isn't perfect but it's closer to correct than not. I think most of the evidence contradicts this. My suspicion is that if we continue to progress at the same rate or accelerate, in 1000 years we (assuming we are still recognizably human) will look back at our understanding of reality right now as nearly completely wrong. So your constraints don't seem to be givens. > My personal view is that there simply aren't any starfaring civilizations to find within a pretty large (1M+ light years) light cone. This makes a lot of assumptions, including that intelligent species don't accelerate quickly into something unrecognizable as they evolve to more advancement, or that our model of spacetime is basically right and there isn't much more to expand into besides our sparse region of reality.
fighterpilot 5y ago
Thought experiment: Suppose every human in China severed their corpus callosum such that they now have two distinct conscious observers in their heads. If my memory is completely wiped, and I'm given the above info and nothing more, should I maintain or increase my probability estimate that I am Chinese (i.e. should I guess 1.4/7.67 or 2.8/(7.67+1.4))?
- onychomys 5y ago
  That's not at all how the CC works. Severing it used to be a common treatment for epilepsy (it prevents the synchronized firing of neurons that cause seizures), and those people were all basically themselves afterwards. https://sites.psu.edu/intropsychsp14n2/2014/02/04/severing-the-corpus-callosum/ https://sites.psu.edu/intropsychsp14n2/2014/02/04/severing-t...
  - fighterpilot 5y ago
    It is how the CC works. They're two separate conscious entities after the CC. See the wiki page on Split-brain for an overview.
    - qayxc 5y ago
      The sad (scary?) part is that one of the two is forever silent.
      - Yoric 5y ago
        I assume that onychomys and fighterpilot are actually two halves of the same brain, debating on HN.
      - deleted 5y ago
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- bmc7505 5y ago
  What is your prior probability that sudden memory loss occurs in the general population?
moralestapia 5y ago
I really like this theory and enjoyed the read, however, the arguments are full of (very naive and) wrong interpretations of statistics and non sequiturs. Examples: "if other sentient species exist, we should expect ours to have an unusually high population" "most planets will have a very much smaller population" "The Earth represents the planet of an ordinary being, and Homo Sapiens represents the species of an ordinary being." ??? what? "Compared to our seven billion strong civilisation, their population will be much smaller. Perhaps only in the tens of millions." "We should expect to be in a large group, not an ordinary one." <- No! This is the author's main flawed argument. You have to look at the distribution of the data. For instance: "you are more likely to have attended a school with more pupils than most other schools", no way, schools have limited attendance and it doesn't follow a power law, i.e. there isn't a school with 1,000,000 students and many small ones with 10 students each, and, even if that were the case, if all of the small 10-student schools make up for 10,000,000 students, the probability of an individual coming from the "big one" is only 10%. Come on, this is common sense. "this also means we should expect to be living on a large planet". This goes against the evidence found, so far. "You might be tempted to think that most of our energy is spent moving around or by fighting against gravity." No. "A species with twice the body mass of another, will on average have half the population density." The plot right before that argument disagrees with that ..., also that plot, named "The probability distribution for the body mass of intelligent species, based on our single piece of data" is nonsense; it has varied greatly throughout the history of life on our planet. "I'm an astrophysicist at the University of Barcelona, formerly a research fellow at the University of Edinburgh, following my PhD at the University of Cambridge." Oh well ... Update: OMG! The guy seems to apply that same line of reasoning to everything: https://twitter.com/frgsimpson/status/895944043645075457 https://twitter.com/frgsimpson/status/895944043645075457 inb4: "Aliens' lifespan should be around 70 years since that's the average for humans, on Earth, at the present time."
- sgt101 5y ago
  You put this brilliantly. Especially the last bit about credentials, what a silly, silly person.
  - 5y ago
sgt101 5y ago
The assumption stated is that we should imagine that we are part of the population of intelligent species and then imagine are we in a big country or a small country.... well the thing is if we say that the country is our species then that says things about homo saps. But we could just as well say that we are in the group of rapidly emerging soon to go extinct species, which would make us typical but with no species specific characteristic. Our biology, morphology and origin are probably irrelevant when characterizing us.
oolonthegreat 5y ago
lots of hand-waving and conclusions pulled out of thin air :(
gizajob 5y ago
The author really needs to bone up on clear arguments and philosophy - this topic is covered more pellucidly and at greater length elsewhere. I couldn't work out what he was arguing for even after scrolling all the way to the end. Amazed someone could get through Phd at Camb. and not have their arsed handed to them repeatedly for poor argumentation. The reasoning throughout seems confused and wooly. Also, 'which begs the question' doesn't mean what the author think it means. Really bored of seeing this phrase misused. 'To beg the question' is a fallacy that occurs when an argument's premises assume the truth of the conclusion, instead of supporting it. What exactly is the argument? Humans are uniquely unique?
idlewords 5y ago
Why don't the larger aliens simply eat the smaller aliens?
- DrJohanson 5y ago
  Because they probably don’t need to eat.
vagabund 5y ago
Why is it more reasonable to expect that the human individual is typical among intelligent lifeforms and thus belongs to an atypical, larger-than-median population and planet, than to expect that earth is a typical habitable planet and that its individuals are atypical?
dang 5y ago
Some past threads: The Big Alien Theory - https://news.ycombinator.com/item?id=23089274 https://news.ycombinator.com/item?id=23089274 - May 2020 (11 comments) The Big Alien Theory - https://news.ycombinator.com/item?id=11358491 https://news.ycombinator.com/item?id=11358491 - March 2016 (7 comments) The Big Alien Theory - https://news.ycombinator.com/item?id=11353239 https://news.ycombinator.com/item?id=11353239 - March 2016 (140 comments)
ncmncm 5y ago
On that note: Aliens Are Slow. http://cantrip.org/slow.pdf http://cantrip.org/slow.pdf
- wyager 5y ago
  This reminds me of the novel Semiosis. Some similar concepts.
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phs 5y ago
> I am more likely to have been born in a high population country than a low population country There are more people who are not me than who are me. Therefore I am more likely to have been born not me than to have been born me.
- alexanderdmitri 5y ago
  I believe this is commonly known to mathematicians as the 'karma is a bitch' rule.
- natosaichek 5y ago
  It's true! If you didn't know who you were, and were asked to take odds on the probability that you were phs, I hope you'd bet that you weren't, 'cause odds are about 10 billion to one against.
- croon 5y ago
  There shouldn't be an I in statistics.
  - titzer 5y ago
    Except we're reasoning about the chain of events that led to us reasoning about the chain of events, so it is inherently self-referential.
- imtringued 5y ago
  The problem is that there is no one on the other side of the bet. The self referential word play obscures the actual bet instance. "There are more people who are not phs than who are phs. Therefore I am more likely to have been born not phs than to have been born phs." "There are more people who are not imtringued than who are imtringued. Therefore I am more likely to have been born not imtringued than to have been born imtringued." The problem becomes obvious, it's a different bet each time and each time all winners are excluded because they never enter into the bet in the first place. E.g. I will never bet "Therefore I am more likely to have been born not phs than to have been born phs." even though it's a clear win for me.
exo-pla-net 5y ago
I feel like a lot of people here are pontificating about something they don't understand. It smells like few people here are mathematicians, and yet they're speaking with reddit levels of hubris, attributing simpletons' logical fallacies to a published astrophysicist. Usually Hacker News is better than this. I'm myself not a mathematician, but I believe I understand his argument, and I see no fallacies. Everything he's written falls out of assuming power laws govern the pertinent quantities. In the absence of additional information, this seems not just valid but the correct starting assumption. I hope we all understand the linked website is a casual release for the public. With the reception he's getting here -- the absolute lack of respect for a professor's passion project -- it's no wonder few scientists bother to engage with the public. He's written a formal paper on this: https://academic.oup.com/mnrasl/article/456/1/L59/2589573 https://academic.oup.com/mnrasl/article/456/1/L59/2589573 A dollar says that his ideas have survived close scrutiny by his colleagues, both mathematicians and astrophysicists. One of them might step in to teach us something, if we were a bit more respectful.
- freshhawk 5y ago
  It certainly uses a logical structure that requires independent variables when we have strong evidence to believe these things are not independent. "if other sentient species exist, we should expect ours to have an unusually high population" Except that sentience evolving is, as far as we know, extremely tied to population numbers and then afterwards sentient agents will have strong incentives to manage their population in some way (or you could say: the odds of them deciding to exactly match their pre-sentient population levels, now that they can make a choice, is small). The underlying explanation of the principle of mediocrity and a mathematical intuition for it is pretty good. Maybe people in 2021 are just extremely skeptical about "if we assume the most likely thing every step and pretend each choice is independent we can build a prediction that we can assume is maximally accurate, which means it is meaningfully accurate" chains of reasoning? That's how you get "Roko's Basilisk scenarios scaring people" type outcomes. It certainly is the source of my distaste and bias against it if I'm being honest with myself.
  - natosaichek 5y ago
plank 5y ago
Read it through (quickly though). One thing that I did not get is why the alien should be around 310kg. If I were to naively use the same arguments: as surely as I am probably from a country with a very high population, and as surely as I probably have a common bloodtype, surely I have probably a very common weight? So should not the average alien bij somewhere around 80-100kg?
- Aransentin 5y ago
  For the average alien, yes. For the average alien species, no.
choeger 5y ago
I don't like these kind of arguments (see doomsday argument) because they do indeed have a deep logical flaw. They use definitions and mechanics from probability theory for phenomena that are not repeatable. For instance, my blood type is not a "likely" or "unlikely" choice out of all existing blood types. It is predetermined to a large degree by my parents. So is my country of birth. Of course, if you pick a human at random, or repeat the test with many different humans, the argument is valid again. But this shows you why the extrapolation to aliens does not work. We don't have any aliens in our sample set. Without postulating a quasi-randon mechanism that made you a human instead of an alien, this argument simply doesn't work. Or rather it doesn't have any meaning.
- setr 5y ago
  The point he’s making is that if you don’t know what the factors are, then your best bet is to pick from the larger group — you’ll be more likely to be correct. If aliens are sufficiently common, then we are much more likely than not to be a “normal” species. It is possible we are not normal, but that’s what a confidence interval is for.
  - adwn 5y ago
    > The point he’s making is that if you don’t know what the factors are, then your best bet is to pick from the larger group — you’ll be more likely to be correct. If your best bet only has a miniscule probability of being right, then your best meta-bet is not to bet. At some point the correct conclusion is to say "We don't know", instead of fooling ourselves with empirically-unsupported navel gazing.
    - croon 5y ago
      "More likely than not" is not a "miniscule probability".
  - choeger 5y ago
    You make a mistake in your argument. Some assumption being "more likely to be correct" has no meaning without a distribution that can be described as random. Without repeating the assumption multiple times the words "probability" or "likelihood" simply cannot be applied.
matco11 5y ago
I like this idea, but I am not convinced about how it is applied here. If they could have made this video a 200 years ago, the population on earth would have been 800mm people, instead of 7.7bn people. Same humans, same planet, but ~10x difference in what our existence implies about population of other forms of life existing out there
- marcus_holmes 5y ago
  Yes, but it covers that - out of all the possible times to make the video, this one is more probable because the population is higher and there are more professors of statistics with free time on their hands. I find the other corollary worrying - we're more likely to be existing at a point in time when we are a higher population than any other. In other words, this is likely to be a high point in human population over time, and our future contains less people than now.
  - nearbuy 5y ago
    That corollary is known as the Doomsday Argument: https://en.wikipedia.org/wiki/Doomsday_argument https://en.wikipedia.org/wiki/Doomsday_argument
  - simiones 5y ago
    The corollary also shows the limitations: you can't actually come up with a real probability for being wrong without knowing other things about this distribution (you can't know how likely you are to be in the most populous time in the history of the human race without knowing the entire past and future history). So the whole argument from statistics holds no water: it depends entirely on other arguments that give a shape to the distribution, and those arguments have their own problems and ways that they can be attacked.
- srcreigh 5y ago
  The predictions actually won't change at all! None of the predictions in the article actually use # of humans as a data point. You aren't gonna input 800m to a calculation and get any different result - no calculation uses that number. The author uses all species of earth to estimate a species size - population density ratio. This works if you remove humans from the equation. The only other data point specific to humans is our weight.
jtolmar 5y ago
When you making predictions about wide ranges of possibilities along many axes, it's very reasonable to choose the single most likely option on each of these, but you end up multiplying some 10% chance by a 20% chance by another 10% chance N layers deep, and the net result still ends up vanishingly unlikely. We are almost certainly not in the most likely possible world. By example, most users on this forum are men from the US born in the 80s or 90s. The most common first name in the US those decades was Mike. The most common surname in the US is Smith. The most populous county in the US is LA County. The single most likely combination of these is that you are Mike Smith from LA County, but you are probably not.
- croon 5y ago
  > We are almost certainly not in the most likely possible world. But we are probably in 9/10 of those likeliest assumptions, even if we don't know which 9.
- folli 5y ago
  But a hypothetical Mike Smith from LA County will be very representative for an average (or median to be more correct) user on this forum. I think that's the point of the article.
kgwgk 5y ago
Related, maybe (I've not read TFA, but the comments about the reasoning made me think of this): https://en.wikipedia.org/wiki/Doomsday_argument https://en.wikipedia.org/wiki/Doomsday_argument
KronisLV 5y ago
That seems like a nicely made webpage! Based on the comments in the source code, it seems like it's made from: https://html5up.net/ https://html5up.net/ Well, maybe it's a bit heavy, but still was pleasant to read.
- kfarr 5y ago
  Fun fact I just made another site last week with an html5up.net theme: https://3d.st https://3d.st
gadf 5y ago
Detractors propose alternate theory explaining data or criticism immediately invalidated.
- Grustaf 5y ago
  Explain what data? We don't have any data at all on aliens.
  - gadf 5y ago
    Well, in the case of that paper it's true. It's using deductive reasoning, but my statement is more easily read about inductive reasoning. However, you could equally read it, "other theories that provide predictions that contradict this reasoning". My point was be constructive and creative, not just dismissive and destructive. Have something to offer, an alternative way of viewing the world, rather than just saying "this way doesn't work". But reading it the way you did, I disagree. We do have plenty of data on aliens. Do we have any "data" on drug-use? On parental abuse? On sexual assault? Most of these "data" are self-reported by people involved. But that's "hard data" from a public health / legal point of view. Equivalently, we have plenty of witness data about actual non-human beings in craft. And we have plenty of data about craft that seem to exceed anything we are capable of. So we have "we do have plenty of data" not "we don't have any data at all" is what you meant to say, if you were reading the world consistently, honestly and openly.
DemocracyFTW 5y ago
I don't think the argument is sound. If I walk into a big room with the general assembly of humankind and shake hands with a random person, that person will probably be from China, Russia, US, India or some such because those few countries have more than 50% of Earth's population. However if I walk into the UN where each state has one seat no matter how small and I shake hands with a random person, that delegate will likely be from a small country because there are many more small countries than big ones. Now if I were to resettle humankind to 250 or so exoplanets and gave each country its own planet, and each planetary civilization eventually brings forth a smart guy who reasons along the lines presented in the Big Alien piece, then I end up with 250 papers or so arguing that surely most exoplanets will have a much smaller population than their own. Almost all the papers will have guessed wrong. Note that while one can always ruin likelihoods by tampering with the data, in this case the exoplanetary populations were modeled on a realistic sample that does follow a power (Zipf, Pareto) law.
- dgudkov 5y ago
  >China, Russia, US, India or some such because those few countries have more than 50% of Earth's population It's interesting that Russia is frequently perceived as a high-population country while in reality by population it's only slightly bigger than Japan and is smaller then Bangladesh, Pakistan, or Nigeria.
  - DemocracyFTW 5y ago
    Sorry bias from someone who's been living ~100m from the iron curtain. Russia's sort of close. But you're right, according to Wikipedia the ranking is (1) China — (2) India — (3) United States — (4) Indonesia — (5) Pakistan — (6) Brazil — (7) Nigeria — (8) Bangladesh — (9) Russia; the first 6 countries (of 241 countries and territories, i.e. 2%) give you 49% of the world's population; 14% of all countries and territories account for 80% of the population, so Pareto more or less.
    - sam_goody 5y ago
      China + India have well over a third of the world's population between them, the next seven largest countries combined (which includes Russia) roughly equal that of China.
pbhjpbhj 5y ago
If you're reading this you're likely to be from Earth; more likely than from some other sentient-life bearing planet; therefore other sentient-life bearing planets must have fewer sentient beings! Simples.
GuB-42 5y ago
For me, it is similar to the doomsday argument[1]. An argument that predicts the likely end of humanity by year 10000, using only statistics. There are 8 rebuttals in the Wikipedia article alone... The problem in the article is that it tries to predict something with nothing but a single data point. In which it explicitly argues that you can: you can have an idea about how fast a human can run by clocking a single human (Usain Bolt). However you have absolutely no way of knowing if it is fast or slow for a human, at least not without making assumptions to create artificial data points. It doesn't mean it is wrong to believe aliens are big, but I think it is wrong to believe anything about how aliens would compare to us using maths alone. Considering that we don't know any aliens, the argument for big aliens have to be somehow backed by observation, physics, chemistry, etc... not just statistics. [1] https://en.wikipedia.org/wiki/Doomsday_argument https://en.wikipedia.org/wiki/Doomsday_argument
sivizius 5y ago
Too many predictions with too many assumptions and too little data.
sivizius 5y ago
Btw. as you can see in the figure about blood type distributions, »I am more likely to have a common blood type than a rare one"« is actually false. It is more likely to have any other type than A. But fair enough, neither of the blood types are very rare.
ac42 5y ago
Using the same line of reasoning, men could argue that the majority of people are men. The whole argument is based on a crude form of survivor bias It's complete and utter bunk.
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reissbaker 5y ago
I believe the author is correct that statistically, most intelligent alien species are likely to be less populous, and more physically massive than, human beings. That being said, at least in the blog post — I haven't read the paper the author also wrote on the subject — there's one critical error, where the author assumes that because most alien species are less populous and more massive, if we ever successfully contact one, we should expect our own species to be more numerous and physically smaller than the contacted alien species. But that assumes contact is based on a random distribution of species! It seems much likelier that contact would be biased just as population size is: that is, we are more likely to contact aliens from a more numerous species than a less numerous one, because they have more spaceships and satellites and listening devices, etc. Using that framework, the contact case actually inverts: the most likely species to contact is the most numerous one, and while it is likely that we are among the most numerous intelligent species, it's not likely that we are the most numerous — at least, not using the country-based datasets. Therefore, it's likely that even though the author is correct that we are more numerous than most, in general alien contact will seem to contradict this, because we will likely be contacting the (relatively few) species that are more numerous than us. We are most likely the Pakistan of the galaxy, but we are also most likely to contact galactic China — not galactic Iceland. The contacted species will also likely be physically smaller than us, for the same reason: contact is biased towards the largest populations, and species with large populations are biased towards physical smallness for thermodynamic reasons. Edit: I read the author's paper, and indeed, the error is not present in the paper (which presumably received more scrutiny) — it's only present in the blog post. The paper instead claims that our nearest intelligent neighbors are likely to be less numerous, physically larger, and from smaller planets — which seems correct. The conclusion of the paper speculates that it may be more useful to search for nearby neighbors than more-numerous far away neighbors, and thus we should prioritize searching nearby systems that have smaller planets (since that's where the neighbors likely are). I'm not necessarily sure that's true — it really depends on whether physics allows reliable semi-FTL travel such as stable wormholes — but it's an interesting take and not immediately controvertible.

147 points by lisper 5y ago

Decades back, Omni Magazine talked to biologists about what dinosaurs could have evolved to if it hadn't been for the meteor. They seemed to have assumed the smart ones would have all been human sized.

867-5309 5y ago
other than birds, crocodilians, etc.
cletus 5y ago
So the thing about the dinosaurs is they were probably always doomed. It just happened to be the meteor that (mostly) finished them off. Why? Well, in times of consistency, the natural trend is for life to get bigger. For herbivores, bigger means access to more vegetation (eg giraffes can eat higher in trees) and is a defense against predators. For predators, size increases the size of prey you can, well, prey on. But as soon as there's a sudden change, size is a disadvantage. You have high food needs (predator or prey). This makes you vulnerable. It's probably more amazing that the dinosaur era lasted >150M years than that this era was ended by a meteor impact.
- booleandilemma 5y ago
  It’s crazy that they lasted > 150M years and never developed intelligence. Meanwhile we’ve been here just 10 million years or so and we’re starting to make it to other planets.
  - nojokes 5y ago
    Perhaps they did but they did not have means to express themselves and modify the environment?
    - booleandilemma 5y ago
      I started thinking about that after I posted. What a shame that would be!
    - nullc 5y ago
      https://pbfcomics.com/comics/dinosaur-meteors/ https://pbfcomics.com/comics/dinosaur-meteors/
  - deleted 5y ago
    [deleted]
  - asdff 5y ago
    Intelligence is usually a huge waste of resources so it's not typically selected for past a certain level. I would still consider my cat highly intelligent with her strategy making during play, and her understanding of human emotions. In the case of our ancestors, there was a time when traditional resource gathering techniques were not as successful as those that took strategy, coordination with others, understanding migrations of other animals and seasonal progressions of edible plants, and potentially even tool use. Those that were intelligent enough to adopt these techniques managed to feed themselves and reproduce, while those lineages that weren't struggled, and eventually died out entirely. The end of the Neanderthal was sort of like this. They failed to improve their hunting strategies, their population shrank especially in competition with early humans, and eventually they died out.
  - cpeterso 5y ago
    Or dinosaurs developed technology, detected the killer meteor, and relocated to Venus.
  - edgyquant 5y ago
    Mammals have been around for more than a hundred million years, maybe as old as the first dinosaurs themselves. 10 million years is about the time humans and gorillas diverged from a common ancestor. We’ve been evolving just as long as every other animal and it was environmental pressures (and luck) that lead to us being what we are.
- majkinetor 5y ago
  Whales seem to have better feeding strategy as they can depend on microbiota.
- sgt101 5y ago
  There were small dinosaurs as well...
  - acjohnson55 5y ago
    Some of them still exist! https://en.wikipedia.org/wiki/Origin_of_birds https://en.wikipedia.org/wiki/Origin_of_birds
    - cletus 5y ago
      That's kind of the point: the _small_ ones still exist.
      - Jorengarenar 5y ago
        And some are crazy intelligent
- catlifeonmars 5y ago
  There were plenty of small dinosaurs.
asdff 5y ago
More large (potentially far more terrifying )flightless birds today, that's probably it.

bryanrasmussen 5y ago

>We cannot learn anything about aliens until we find them" >The above statement might sound reasonable, and intuitive, but it lacks justification. Standing on its own, it’s just a piece of dogma. well let's try the following statement then 1. Most things that are learned about are observed to exist before being studied. There are rare items of knowledge that are cogitated upon first and found to exist later, but in general things that you learn about will be like most of the things that you learn about - they will be observed as existing and then be studied.

dwohnitmok 5y ago
> Most things that are learned about are observed to exist before being studied. Is this true at this point for physics and astronomy? I have no idea what the relative proportion of discoveries are "this was predicted to exist and we found it!" vs "whoa this is totally unexpected." I suspect that there's also a ton of things in the middle, where an anomalous reading that doesn't directly show the existence of something but does show the deficiency of a theory then leads to corrections in the theory which then result in another cascade of predictions of existence from the theory.
sorokod 5y ago
A lot of math is done by working on conjectures that take time to prove or disprove.
- phkahler 5y ago
  Conjectures in math are based on observations and intuition gained from related observable things. Specifically they seem to be statements about properties of things already known.
  - sorokod 5y ago
    Allowing the word "related" to do a lot of heavy lifting, I'd say that it is the same for aliens.
  - neonological 5y ago

bostonsre 5y ago

If larger aliens means smaller populations of aliens, would that mean that there are fewer possibilities for einsteins to come into existence? If einsteins are less likely, I could see the rate of growth of civilizations being slower, but no real intuition of whether or not that would make much of a difference in the long term.

thisiscorrect 5y ago
Does this assume that the likelihood of each alien to be an "einstein" remains constant with size? It seems like a larger being which can support a larger brain might stand a better chance to develop higher thoughts.
- teruakohatu 5y ago
  Larger brains don't necessarily mean higher cognitive function. Humans have smaller brains than African elephants and many dolphin and whale species.
  - fighterpilot 5y ago
    "Necessarily" is a standard that's too strict and binary. The relevant question is to what extent brain size facilitates and is correlated with intelligence. It doesn't seem to be irrelevant. Large brains are correlated with higher IQ within humans. Also, humans' intelligence came about with an almost doubling in brain volume over two million years. Across very different species there is a weaker correlation but it still seems to be positive. Whales and dolphins are far smarter than ants. Octopuses seem to be an outlier in that respect. I think it's fair to say that the probability of an "Einstein" is positively correlated with body mass, and therefore negatively correlated with population density, at least up to a point (whether that correlation turns negative beyond a point can be debated).
    - baja_blast 5y ago
      Bird brains, such as parrot and crows so that brain size is not everything. A crows brain is smaller than a chimps in overall size and body:brain ratio, yet crows show more complex social behavior, problem solving and tool use (despite not having hands). Bird's brains are much denser than mammals, so it's less size and more number of neurons, and the complexity of how these neurons are networked.

deleted 5y ago

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Semiapies 5y ago

At some point, this sort of thing turns into a weird inverse of naive copernicanism. I look forward to the version of this argument that concludes that we statistically must be the giant aliens and everyone else in the universe is probably hobbit-sized. ETA: or the copernican wrap-around: "Any random person is more likely to be near an average size than not, so...[five dubious steps later]...obviously aliens are mostly going to be average human-sized."

shakezula 5y ago
I take this the same way I take the Drake equations: As an interesting thought experiment but only as good as the assumptions they make. But I will say this is based on entirely reasonable assumptions and observations. It's an interesting argument as I've always been of the opinion that life is abundant but the universe so large that it's still quite spread out.
- mortenjorck 5y ago
  > I've always been of the opinion that life is abundant but the universe so large that it's still quite spread out. This is basically my optimistic/pessimistic view of alien life. The scale of the universe means the probability of alien life existing must be essentially 100%, while the scale of the universe also means the probability of any life finding another instance of life must be essentially 0%. Although a fun corollary inspired by the Big Alien thought experiment is that local maxima must also exist: Somewhere, some planet with intelligent life must have been close enough to another such planet that they did indeed find each other.
  - shakezula 5y ago
    > local maxima must also exist Interesting point. It follows that as we can observe how galaxies and clusters form, it must follow that if life requires a star, it would cluster and group similarly, and eventually group closely enough for two intelligent species to bump into one another.
    - 5y ago

cletus 5y ago

I'm usually a skeptic but I don't buy into the idea that we can't reason anything about aliens until we find them. Some things are just physics. Physics places absolute limits on how small or large an organism can be, for example. It's why I'm not worried about the possibility of superintelligent viruses. There is a long theory of the value of thought experiments in science. The word "atom" is derived from the Greek "atomos", which was the result of a 2000+ year old thought experiment about if something was infinitely divisible or not. Experimental evidence didn't come until the 1800s (IIRC). It seems weird that any article talking about possible alien life doesn't at least touch on the anthropic principle, which is a whole set of thought experiments. My personal view is that our knowledge of the Universe at this point isn't perfect but it's closer to correct than not. That means (IMHO) the speed of light is an absolute limit and thermodynamics holds true. With just those two things, you have a lot of constraints and you can start making some observations. For example: a burgeoning civilization needs energy (and matter), will produce waste heat and that waste heat has to go somewhere. This of course touches on various thought experiments relating to the Fermi Paradox. My personal view is that there simply aren't any starfaring civilizations to find within a pretty large (1M+ light years) light cone. And if you look at the Milky Way, if there aren't any to find now, it's highly unlikely there other civilizations beyond our light cone just because of the low probability of two (or more) such civilizations evolving to that point within 100,000 years of each other.

colordrops 5y ago
> superintelligent viruses What if some virus evolved to work super intelligently as a hive mind? > My personal view is that our knowledge of the Universe at this point isn't perfect but it's closer to correct than not. I think most of the evidence contradicts this. My suspicion is that if we continue to progress at the same rate or accelerate, in 1000 years we (assuming we are still recognizably human) will look back at our understanding of reality right now as nearly completely wrong. So your constraints don't seem to be givens. > My personal view is that there simply aren't any starfaring civilizations to find within a pretty large (1M+ light years) light cone. This makes a lot of assumptions, including that intelligent species don't accelerate quickly into something unrecognizable as they evolve to more advancement, or that our model of spacetime is basically right and there isn't much more to expand into besides our sparse region of reality.

fighterpilot 5y ago

Thought experiment: Suppose every human in China severed their corpus callosum such that they now have two distinct conscious observers in their heads. If my memory is completely wiped, and I'm given the above info and nothing more, should I maintain or increase my probability estimate that I am Chinese (i.e. should I guess 1.4/7.67 or 2.8/(7.67+1.4))?

onychomys 5y ago
That's not at all how the CC works. Severing it used to be a common treatment for epilepsy (it prevents the synchronized firing of neurons that cause seizures), and those people were all basically themselves afterwards. https://sites.psu.edu/intropsychsp14n2/2014/02/04/severing-the-corpus-callosum/ https://sites.psu.edu/intropsychsp14n2/2014/02/04/severing-t...
- fighterpilot 5y ago
  It is how the CC works. They're two separate conscious entities after the CC. See the wiki page on Split-brain for an overview.
  - qayxc 5y ago
    The sad (scary?) part is that one of the two is forever silent.
    - Yoric 5y ago
      I assume that onychomys and fighterpilot are actually two halves of the same brain, debating on HN.
    - deleted 5y ago
      [deleted]
bmc7505 5y ago
What is your prior probability that sudden memory loss occurs in the general population?

moralestapia 5y ago

I really like this theory and enjoyed the read, however, the arguments are full of (very naive and) wrong interpretations of statistics and non sequiturs. Examples: "if other sentient species exist, we should expect ours to have an unusually high population" "most planets will have a very much smaller population" "The Earth represents the planet of an ordinary being, and Homo Sapiens represents the species of an ordinary being." ??? what? "Compared to our seven billion strong civilisation, their population will be much smaller. Perhaps only in the tens of millions." "We should expect to be in a large group, not an ordinary one." <- No! This is the author's main flawed argument. You have to look at the distribution of the data. For instance: "you are more likely to have attended a school with more pupils than most other schools", no way, schools have limited attendance and it doesn't follow a power law, i.e. there isn't a school with 1,000,000 students and many small ones with 10 students each, and, even if that were the case, if all of the small 10-student schools make up for 10,000,000 students, the probability of an individual coming from the "big one" is only 10%. Come on, this is common sense. "this also means we should expect to be living on a large planet". This goes against the evidence found, so far. "You might be tempted to think that most of our energy is spent moving around or by fighting against gravity." No. "A species with twice the body mass of another, will on average have half the population density." The plot right before that argument disagrees with that ..., also that plot, named "The probability distribution for the body mass of intelligent species, based on our single piece of data" is nonsense; it has varied greatly throughout the history of life on our planet. "I'm an astrophysicist at the University of Barcelona, formerly a research fellow at the University of Edinburgh, following my PhD at the University of Cambridge." Oh well ... Update: OMG! The guy seems to apply that same line of reasoning to everything: https://twitter.com/frgsimpson/status/895944043645075457 https://twitter.com/frgsimpson/status/895944043645075457 inb4: "Aliens' lifespan should be around 70 years since that's the average for humans, on Earth, at the present time."

sgt101 5y ago
You put this brilliantly. Especially the last bit about credentials, what a silly, silly person.
- 5y ago

sgt101 5y ago

The assumption stated is that we should imagine that we are part of the population of intelligent species and then imagine are we in a big country or a small country.... well the thing is if we say that the country is our species then that says things about homo saps. But we could just as well say that we are in the group of rapidly emerging soon to go extinct species, which would make us typical but with no species specific characteristic. Our biology, morphology and origin are probably irrelevant when characterizing us.

oolonthegreat 5y ago

lots of hand-waving and conclusions pulled out of thin air :(

gizajob 5y ago

The author really needs to bone up on clear arguments and philosophy - this topic is covered more pellucidly and at greater length elsewhere. I couldn't work out what he was arguing for even after scrolling all the way to the end. Amazed someone could get through Phd at Camb. and not have their arsed handed to them repeatedly for poor argumentation. The reasoning throughout seems confused and wooly. Also, 'which begs the question' doesn't mean what the author think it means. Really bored of seeing this phrase misused. 'To beg the question' is a fallacy that occurs when an argument's premises assume the truth of the conclusion, instead of supporting it. What exactly is the argument? Humans are uniquely unique?

idlewords 5y ago

Why don't the larger aliens simply eat the smaller aliens?

DrJohanson 5y ago
Because they probably don’t need to eat.

vagabund 5y ago

Why is it more reasonable to expect that the human individual is typical among intelligent lifeforms and thus belongs to an atypical, larger-than-median population and planet, than to expect that earth is a typical habitable planet and that its individuals are atypical?

dang 5y ago

Some past threads: The Big Alien Theory - https://news.ycombinator.com/item?id=23089274 https://news.ycombinator.com/item?id=23089274 - May 2020 (11 comments) The Big Alien Theory - https://news.ycombinator.com/item?id=11358491 https://news.ycombinator.com/item?id=11358491 - March 2016 (7 comments) The Big Alien Theory - https://news.ycombinator.com/item?id=11353239 https://news.ycombinator.com/item?id=11353239 - March 2016 (140 comments)

ncmncm 5y ago

On that note: Aliens Are Slow. http://cantrip.org/slow.pdf http://cantrip.org/slow.pdf

wyager 5y ago
This reminds me of the novel Semiosis. Some similar concepts.

deleted 5y ago

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phs 5y ago

> I am more likely to have been born in a high population country than a low population country There are more people who are not me than who are me. Therefore I am more likely to have been born not me than to have been born me.

alexanderdmitri 5y ago
I believe this is commonly known to mathematicians as the 'karma is a bitch' rule.
natosaichek 5y ago
It's true! If you didn't know who you were, and were asked to take odds on the probability that you were phs, I hope you'd bet that you weren't, 'cause odds are about 10 billion to one against.
croon 5y ago
There shouldn't be an I in statistics.
- titzer 5y ago
  Except we're reasoning about the chain of events that led to us reasoning about the chain of events, so it is inherently self-referential.
imtringued 5y ago
The problem is that there is no one on the other side of the bet. The self referential word play obscures the actual bet instance. "There are more people who are not phs than who are phs. Therefore I am more likely to have been born not phs than to have been born phs." "There are more people who are not imtringued than who are imtringued. Therefore I am more likely to have been born not imtringued than to have been born imtringued." The problem becomes obvious, it's a different bet each time and each time all winners are excluded because they never enter into the bet in the first place. E.g. I will never bet "Therefore I am more likely to have been born not phs than to have been born phs." even though it's a clear win for me.

exo-pla-net 5y ago

I feel like a lot of people here are pontificating about something they don't understand. It smells like few people here are mathematicians, and yet they're speaking with reddit levels of hubris, attributing simpletons' logical fallacies to a published astrophysicist. Usually Hacker News is better than this. I'm myself not a mathematician, but I believe I understand his argument, and I see no fallacies. Everything he's written falls out of assuming power laws govern the pertinent quantities. In the absence of additional information, this seems not just valid but the correct starting assumption. I hope we all understand the linked website is a casual release for the public. With the reception he's getting here -- the absolute lack of respect for a professor's passion project -- it's no wonder few scientists bother to engage with the public. He's written a formal paper on this: https://academic.oup.com/mnrasl/article/456/1/L59/2589573 https://academic.oup.com/mnrasl/article/456/1/L59/2589573 A dollar says that his ideas have survived close scrutiny by his colleagues, both mathematicians and astrophysicists. One of them might step in to teach us something, if we were a bit more respectful.

freshhawk 5y ago
It certainly uses a logical structure that requires independent variables when we have strong evidence to believe these things are not independent. "if other sentient species exist, we should expect ours to have an unusually high population" Except that sentience evolving is, as far as we know, extremely tied to population numbers and then afterwards sentient agents will have strong incentives to manage their population in some way (or you could say: the odds of them deciding to exactly match their pre-sentient population levels, now that they can make a choice, is small). The underlying explanation of the principle of mediocrity and a mathematical intuition for it is pretty good. Maybe people in 2021 are just extremely skeptical about "if we assume the most likely thing every step and pretend each choice is independent we can build a prediction that we can assume is maximally accurate, which means it is meaningfully accurate" chains of reasoning? That's how you get "Roko's Basilisk scenarios scaring people" type outcomes. It certainly is the source of my distaste and bias against it if I'm being honest with myself.
- natosaichek 5y ago

plank 5y ago

Read it through (quickly though). One thing that I did not get is why the alien should be around 310kg. If I were to naively use the same arguments: as surely as I am probably from a country with a very high population, and as surely as I probably have a common bloodtype, surely I have probably a very common weight? So should not the average alien bij somewhere around 80-100kg?

Aransentin 5y ago
For the average alien, yes. For the average alien species, no.

choeger 5y ago

I don't like these kind of arguments (see doomsday argument) because they do indeed have a deep logical flaw. They use definitions and mechanics from probability theory for phenomena that are not repeatable. For instance, my blood type is not a "likely" or "unlikely" choice out of all existing blood types. It is predetermined to a large degree by my parents. So is my country of birth. Of course, if you pick a human at random, or repeat the test with many different humans, the argument is valid again. But this shows you why the extrapolation to aliens does not work. We don't have any aliens in our sample set. Without postulating a quasi-randon mechanism that made you a human instead of an alien, this argument simply doesn't work. Or rather it doesn't have any meaning.

setr 5y ago
The point he’s making is that if you don’t know what the factors are, then your best bet is to pick from the larger group — you’ll be more likely to be correct. If aliens are sufficiently common, then we are much more likely than not to be a “normal” species. It is possible we are not normal, but that’s what a confidence interval is for.
- adwn 5y ago
  > The point he’s making is that if you don’t know what the factors are, then your best bet is to pick from the larger group — you’ll be more likely to be correct. If your best bet only has a miniscule probability of being right, then your best meta-bet is not to bet. At some point the correct conclusion is to say "We don't know", instead of fooling ourselves with empirically-unsupported navel gazing.
  - croon 5y ago
    "More likely than not" is not a "miniscule probability".
- choeger 5y ago
  You make a mistake in your argument. Some assumption being "more likely to be correct" has no meaning without a distribution that can be described as random. Without repeating the assumption multiple times the words "probability" or "likelihood" simply cannot be applied.

matco11 5y ago

I like this idea, but I am not convinced about how it is applied here. If they could have made this video a 200 years ago, the population on earth would have been 800mm people, instead of 7.7bn people. Same humans, same planet, but ~10x difference in what our existence implies about population of other forms of life existing out there

marcus_holmes 5y ago
Yes, but it covers that - out of all the possible times to make the video, this one is more probable because the population is higher and there are more professors of statistics with free time on their hands. I find the other corollary worrying - we're more likely to be existing at a point in time when we are a higher population than any other. In other words, this is likely to be a high point in human population over time, and our future contains less people than now.
- nearbuy 5y ago
  That corollary is known as the Doomsday Argument: https://en.wikipedia.org/wiki/Doomsday_argument https://en.wikipedia.org/wiki/Doomsday_argument
- simiones 5y ago
  The corollary also shows the limitations: you can't actually come up with a real probability for being wrong without knowing other things about this distribution (you can't know how likely you are to be in the most populous time in the history of the human race without knowing the entire past and future history). So the whole argument from statistics holds no water: it depends entirely on other arguments that give a shape to the distribution, and those arguments have their own problems and ways that they can be attacked.
srcreigh 5y ago
The predictions actually won't change at all! None of the predictions in the article actually use # of humans as a data point. You aren't gonna input 800m to a calculation and get any different result - no calculation uses that number. The author uses all species of earth to estimate a species size - population density ratio. This works if you remove humans from the equation. The only other data point specific to humans is our weight.

jtolmar 5y ago

When you making predictions about wide ranges of possibilities along many axes, it's very reasonable to choose the single most likely option on each of these, but you end up multiplying some 10% chance by a 20% chance by another 10% chance N layers deep, and the net result still ends up vanishingly unlikely. We are almost certainly not in the most likely possible world. By example, most users on this forum are men from the US born in the 80s or 90s. The most common first name in the US those decades was Mike. The most common surname in the US is Smith. The most populous county in the US is LA County. The single most likely combination of these is that you are Mike Smith from LA County, but you are probably not.

croon 5y ago
> We are almost certainly not in the most likely possible world. But we are probably in 9/10 of those likeliest assumptions, even if we don't know which 9.
folli 5y ago
But a hypothetical Mike Smith from LA County will be very representative for an average (or median to be more correct) user on this forum. I think that's the point of the article.

kgwgk 5y ago

Related, maybe (I've not read TFA, but the comments about the reasoning made me think of this): https://en.wikipedia.org/wiki/Doomsday_argument https://en.wikipedia.org/wiki/Doomsday_argument

KronisLV 5y ago

That seems like a nicely made webpage! Based on the comments in the source code, it seems like it's made from: https://html5up.net/ https://html5up.net/ Well, maybe it's a bit heavy, but still was pleasant to read.

kfarr 5y ago
Fun fact I just made another site last week with an html5up.net theme: https://3d.st https://3d.st

gadf 5y ago

Detractors propose alternate theory explaining data or criticism immediately invalidated.

Grustaf 5y ago
Explain what data? We don't have any data at all on aliens.
- gadf 5y ago
  Well, in the case of that paper it's true. It's using deductive reasoning, but my statement is more easily read about inductive reasoning. However, you could equally read it, "other theories that provide predictions that contradict this reasoning". My point was be constructive and creative, not just dismissive and destructive. Have something to offer, an alternative way of viewing the world, rather than just saying "this way doesn't work". But reading it the way you did, I disagree. We do have plenty of data on aliens. Do we have any "data" on drug-use? On parental abuse? On sexual assault? Most of these "data" are self-reported by people involved. But that's "hard data" from a public health / legal point of view. Equivalently, we have plenty of witness data about actual non-human beings in craft. And we have plenty of data about craft that seem to exceed anything we are capable of. So we have "we do have plenty of data" not "we don't have any data at all" is what you meant to say, if you were reading the world consistently, honestly and openly.

DemocracyFTW 5y ago

I don't think the argument is sound. If I walk into a big room with the general assembly of humankind and shake hands with a random person, that person will probably be from China, Russia, US, India or some such because those few countries have more than 50% of Earth's population. However if I walk into the UN where each state has one seat no matter how small and I shake hands with a random person, that delegate will likely be from a small country because there are many more small countries than big ones. Now if I were to resettle humankind to 250 or so exoplanets and gave each country its own planet, and each planetary civilization eventually brings forth a smart guy who reasons along the lines presented in the Big Alien piece, then I end up with 250 papers or so arguing that surely most exoplanets will have a much smaller population than their own. Almost all the papers will have guessed wrong. Note that while one can always ruin likelihoods by tampering with the data, in this case the exoplanetary populations were modeled on a realistic sample that does follow a power (Zipf, Pareto) law.

dgudkov 5y ago
>China, Russia, US, India or some such because those few countries have more than 50% of Earth's population It's interesting that Russia is frequently perceived as a high-population country while in reality by population it's only slightly bigger than Japan and is smaller then Bangladesh, Pakistan, or Nigeria.
- DemocracyFTW 5y ago
  Sorry bias from someone who's been living ~100m from the iron curtain. Russia's sort of close. But you're right, according to Wikipedia the ranking is (1) China — (2) India — (3) United States — (4) Indonesia — (5) Pakistan — (6) Brazil — (7) Nigeria — (8) Bangladesh — (9) Russia; the first 6 countries (of 241 countries and territories, i.e. 2%) give you 49% of the world's population; 14% of all countries and territories account for 80% of the population, so Pareto more or less.
  - sam_goody 5y ago
    China + India have well over a third of the world's population between them, the next seven largest countries combined (which includes Russia) roughly equal that of China.

pbhjpbhj 5y ago

If you're reading this you're likely to be from Earth; more likely than from some other sentient-life bearing planet; therefore other sentient-life bearing planets must have fewer sentient beings! Simples.

GuB-42 5y ago

For me, it is similar to the doomsday argument[1]. An argument that predicts the likely end of humanity by year 10000, using only statistics. There are 8 rebuttals in the Wikipedia article alone... The problem in the article is that it tries to predict something with nothing but a single data point. In which it explicitly argues that you can: you can have an idea about how fast a human can run by clocking a single human (Usain Bolt). However you have absolutely no way of knowing if it is fast or slow for a human, at least not without making assumptions to create artificial data points. It doesn't mean it is wrong to believe aliens are big, but I think it is wrong to believe anything about how aliens would compare to us using maths alone. Considering that we don't know any aliens, the argument for big aliens have to be somehow backed by observation, physics, chemistry, etc... not just statistics. [1] https://en.wikipedia.org/wiki/Doomsday_argument https://en.wikipedia.org/wiki/Doomsday_argument

sivizius 5y ago

Too many predictions with too many assumptions and too little data.

sivizius 5y ago

Btw. as you can see in the figure about blood type distributions, »I am more likely to have a common blood type than a rare one"« is actually false. It is more likely to have any other type than A. But fair enough, neither of the blood types are very rare.

ac42 5y ago

Using the same line of reasoning, men could argue that the majority of people are men. The whole argument is based on a crude form of survivor bias It's complete and utter bunk.

deleted 5y ago

[deleted]

reissbaker 5y ago

I believe the author is correct that statistically, most intelligent alien species are likely to be less populous, and more physically massive than, human beings. That being said, at least in the blog post — I haven't read the paper the author also wrote on the subject — there's one critical error, where the author assumes that because most alien species are less populous and more massive, if we ever successfully contact one, we should expect our own species to be more numerous and physically smaller than the contacted alien species. But that assumes contact is based on a random distribution of species! It seems much likelier that contact would be biased just as population size is: that is, we are more likely to contact aliens from a more numerous species than a less numerous one, because they have more spaceships and satellites and listening devices, etc. Using that framework, the contact case actually inverts: the most likely species to contact is the most numerous one, and while it is likely that we are among the most numerous intelligent species, it's not likely that we are the most numerous — at least, not using the country-based datasets. Therefore, it's likely that even though the author is correct that we are more numerous than most, in general alien contact will seem to contradict this, because we will likely be contacting the (relatively few) species that are more numerous than us. We are most likely the Pakistan of the galaxy, but we are also most likely to contact galactic China — not galactic Iceland. The contacted species will also likely be physically smaller than us, for the same reason: contact is biased towards the largest populations, and species with large populations are biased towards physical smallness for thermodynamic reasons. Edit: I read the author's paper, and indeed, the error is not present in the paper (which presumably received more scrutiny) — it's only present in the blog post. The paper instead claims that our nearest intelligent neighbors are likely to be less numerous, physically larger, and from smaller planets — which seems correct. The conclusion of the paper speculates that it may be more useful to search for nearby neighbors than more-numerous far away neighbors, and thus we should prioritize searching nearby systems that have smaller planets (since that's where the neighbors likely are). I'm not necessarily sure that's true — it really depends on whether physics allows reliable semi-FTL travel such as stable wormholes — but it's an interesting take and not immediately controvertible.