The Big Alien Theory

&gt;No matter what degree of variability is chosen, alien planets are very unlikely to be much larger than the Earth. To be specific, we can say with 95% confidence that another planet with intelligent life, such as our nearest neighbour, will have a circumference no more than 20% greater than that of the Earth.<p>Huh? I see no justification for this.<p>I&#x27;m firmly in the &quot;We know nothing about aliens and won&#x27;t until we get some hard data&quot; camp.<p>Alien life will, by definition, be alien. We have no basis for assuming it&#x27;s even going to be recognisable as life.<p>Life essentially seems to be a persistent self-reproducing dissipative structure that responds to evolutionary pressure. There is nothing in the manual that requires liquid water, gravity, a planetary surface, carbon, or any of the other ingredients that define life on Earth.

So they do something like this: Let&#x27;s choose a human in random - he is more probable to be from Pakistan than from Slovakia. (OK) Now let&#x27;s choose a country - now an average country like Slovakia is more probable than a country as big as Pakistan. (OK)<p>So if you are a human - then it is most probable that you live in a country that is more populous than the typical country. (OK)<p>Now they say - ok - so now instead of choosing humans let&#x27;s do the same thing with sentient beings. If you are a sentient being it is more probable that you live on a planet where there are many other sentient beings rather than on a planet that there are few of them. But if you go to some random planet with sentient life - then the expected number of sentient beings there would be average.<p>Then it goes on that &quot;Physically larger species will on average have lower population densities.&quot; - so most probably the random alien planet will have fewer and larger sentient beings than us.<p>I don&#x27;t know if I buy that whole argument - but I am too lazy to write the bayesian equations to nail it down.

This is a bit like the sleeping beauty paradox. [1] We have to be careful what we&#x27;re sampling.<p>Is it individuals or civilizations?<p>An average civilization will be average sized. An average individual will belong to a larger-than average civilization.<p>It&#x27;s also a bit like the problem that in average, your friends have more friends than you do. (That&#x27;s easy to understand. It&#x27;s because they are not a really random sample of all people. People with more connections are over-represented in your friends.)<p>If we assume that observation doesn&#x27;t depend on civilization size, then we&#x27;re sampling civilizations, and on average would find average sized civilizations.<p>If we assume that we observe individuals and not civilizations, then we&#x27;re sampling individuals and are likely to see individuals of a big civilization.<p>Now, if I look at myself, if I&#x27;m a random sample from all individuals in the galaxy, it&#x27;s likely that I&#x27;m part of a large civilization. That would mean other civilizations would on average be smaller than mine.<p>If I look at my civilization, and assume it&#x27;s a random sample from all the civilizations in the galaxy, it&#x27;s likely that it&#x27;s an average sized civilization. A random other individual in the galaxy would be likely from a larger civilization.<p>I don&#x27;t think either way of thinking is really justified.<p>You can extend this to a doomsday argument by the way. Since I am alive now, it&#x27;s most likely that most people are alive now. Hence in the past and in the future, there will be less people alive.<p>1: <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=10149286" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=10149286</a>

&quot;Not even wrong&quot;. This entire analysis is built on reasonable statistics which are predicated on dubious and unprovable assumptions, which invalidate the entire thing.<p>Consider &quot;the size of alien species&quot;. Okay... so we are extrapolating about the size of beings we know nothing about based on those beings that have come to existence in our particular situation? Assuming that the distribution of weight across animals on Earth is the same as the distribution of weight across beings in the universe is dubious.<p>This is a wonderful example of Brandolini&#x27;s law.

I&#x27;m unclear on why the author posits that we should assume a smaller population necessarily means the average being will be larger.<p>For example, if a human did this thought experiment 2000 years ago - a blink of the eye in the scale we are talking about - we would have perhaps 500,000,000 humans on the planet, or something along those lines. We have 14x as many humans now.<p>Yet we have not shrunk in size as the species has grown in population, and if anything, have grown larger.<p>If we look at the total biomass on earth, we are a fairly small portion of it. So shouldn&#x27;t we assume, as we are assuming our situation is average, that intelligent aliens are also a fairly small portion of their planet&#x27;s biomass? And if so, wouldn&#x27;t the size of the aliens themselves be something that has very little to do with the total energy reaching the planet surface?<p>I get that it&#x27;s just statistical probability and math, and it&#x27;s fun, but this particular thing stuck out for me.<p>It was a fun read regardless, so thank you for the break from work!

Interesting use of inference. Kinda feels like it ignores many of the discussions (or my limited understanding of them) around the Fermi paradox <a href="http:&#x2F;&#x2F;waitbutwhy.com&#x2F;2014&#x2F;05&#x2F;fermi-paradox.html" rel="nofollow">http:&#x2F;&#x2F;waitbutwhy.com&#x2F;2014&#x2F;05&#x2F;fermi-paradox.html</a><p>In summary: &quot;We’re rare, we’re first, or we’re fucked.&quot;<p>The article seems to assume that there are lots of populations just because there are lots of planets. But the time that those planets have been around matters too.

I can&#x27;t wrap my head around the &quot;we should expect to be in a large group&quot;.<p>We, as a single species, found to the question &quot;is there alien life besides us?&quot;. I&#x27;m no individual independent from the culture of our species. I don&#x27;t come up with this question randomly, you pointed me to this today.<p>The other way around: I have to expect to be in the large group only, if the large group makes it more likely that someone in it has questions about his group (more members -&gt; more random thoughts -&gt; greater total of thoughts about which group one is in). This is true for blood types (unless people with weird blood types commonly get in to issues making them wonder about their blood type...). But for aliens, probably either more or less all wonder collectively through cultural exchange, or it wasn&#x27;t part of a public debate.<p>Hm, you get the knot in my brain? can you solve it?

Great thought experiment.<p>I would have thought that a planet&#x27;s life form, shape and variety would be determined by:<p>1- the energy output of nearest star<p>2- the planet&#x27;s gravity<p>He barely mentions gravity which is surprising. Earthlings probably wouldn&#x27;t be as tall with 1.3x more gravity. Maybe life wouldn&#x27;t even have made it out of water, or much more slowly.<p>Evolution would mean &quot;heavier&quot; eggs would be harder to carry. The entire evolution process hangs around reproduction so what would that mean?<p>Same for less gravity - except it would _probably_ be on a smaller planet. Gravity correlates with planet size in the solar system. Would &lt;0.8G be enough to retain water, atmosphere, etc?<p>Somehow I&#x27;m not surprised to find out one day that an intelligent alien life would look a lot like us, on a planet that looks a lot like Earth.

&gt; Within the context of the animal kingdom, our species&#x27; position is clear. Aside from a disproportionately large brain, we&#x27;re fairly ordinary mammals.<p>Oh yeah? :) <a href="http:&#x2F;&#x2F;prokopetz.tumblr.com&#x2F;post&#x2F;57702943181&#x2F;mikhailvladimirovich-bogleech-its-funny-how" rel="nofollow">http:&#x2F;&#x2F;prokopetz.tumblr.com&#x2F;post&#x2F;57702943181&#x2F;mikhailvladimir...</a>

This analysis is based on many unjustified assumptions. I don&#x27;t think we can go reliably very far on this route.<p>However, I do think that we can scientifically study some aliens today, or more precisely what we can see from them, through the UFO phenomenon. Yes, that thing! For me the only paradox in the Fermi paradox is that the UFO phenomenon is boycotted as a manifestation of Aliens on earth.<p>The following three articles are a product of such study. They present a new electromagnetic propulsion system called PEMP inspired by the data of UFO observations. It also present a totally innovative method to produce the intense EM fields required by this propulsion system. These are currently only theories waiting for an experimental validation. The author is a physic theorist, not an experimentalist.<p>&quot;Pulsed EM Propulsion of Unconventional Flying Objects&quot;:<a href="http:&#x2F;&#x2F;www.meessen.net&#x2F;AMeessen&#x2F;Propulsion.pdf" rel="nofollow">http:&#x2F;&#x2F;www.meessen.net&#x2F;AMeessen&#x2F;Propulsion.pdf</a><p>&quot;Evidence of Very Strong Low Frequency Magnetic Fields&quot;: <a href="http:&#x2F;&#x2F;www.meessen.net&#x2F;AMeessen&#x2F;Evidence.pdf" rel="nofollow">http:&#x2F;&#x2F;www.meessen.net&#x2F;AMeessen&#x2F;Evidence.pdf</a><p>&quot;Production of EM Surface Waves by Superconducting Spheres: A New Type of Harmonic Oscillators&quot;: <a href="http:&#x2F;&#x2F;www.meessen.net&#x2F;AMeessen&#x2F;Production.pdf" rel="nofollow">http:&#x2F;&#x2F;www.meessen.net&#x2F;AMeessen&#x2F;Production.pdf</a><p>So there is no need to speculate. Just open your eyes and look at the data we already have for so many years.<p>Note that this is the product of an inductive research process. The initial working hypothesis was that UFO are real and witnesses report real data on them. Now see if we can derive a valid propulsion system matching the described artifacts using only conventional physics law.<p>It was initially a test, an experiment on a pure theoretical ground. The test is apparently conclusive. We now have a theory we can test in our lab and we could validate a disruptive discovery.<p>Objectively, we still don&#x27;t know if UFOs are real and they are aliens visiting earth. But we now have an opportunity to indirectly test that possibility with pure solid ground science and engineering. Thanks to these theories.

I don&#x27;t get the stats here:<p>- I am an ordinary sentient being (for the sake of argument... just nod)<p>- I am a member of an ordinary species.<p>according this theory one of these statements is wrong.

Serious question; why are people willing to seriously entertain the idea of aliens, but not gods?

I think some of the math going on here is interesting and probably has some interesting consequences for people&#x27;s expectations about means. But I&#x27;m not sure about that paper...<p>I want to be generous here and assume I&#x27;m misunderstanding, but it does seem a bit like the argument begs the question a bit.<p>The intended conclusion is that we should consider non-earth-like (i.e. non-earth-sized) planets as just as likely to be inhabited as earth-like planets. Which is to say that we shouldn&#x27;t expect that population density is strongly correlated with planet size.<p>And this is shown starting from a model where &quot;mean population density is invariant to planet size&quot;. Hmm...

Something not mentioned here is the relationship between oxygen levels in the atmosphere and the size of animals on a planet. During the era of giant creatures (dinosaurs) the atmosphere was around 35% oxygen, today it is about 21%.

This strikes me as very similar to the simulation argument. That is most beings probably exist in simulations, and therefore you are far more likely to exist in a simulation than be a living person. Or similar anthropic arguments could be made about many things. You are more likely to be living in a bigger country, you are more likely to be living in the period of time where Earth&#x27;s population is the largest, etc.

Interesting analysis, but after reading the FAQ at the bottom, it rests upon quite a few important hidden assumptions. For example:<p>&gt;However if there is any hope of finding life on other planets, there must be a huge number of planets with life in the Universe. Therefore, for the case we&#x27;re interested in...<p>So during the entire analysis, we were limiting ourselves <i>only to those universes in which we do make alien contact</i>, regardless of how likely <i>that</i> event is.

Reminds me of Joe Polchinski&#x27;s calculation[1] that the probability of the multiverse is 94%.<p>Unbridled Physics-ism (as in [2]) and Bayesianism definitely don&#x27;t mix well.<p>[1] <a href="http:&#x2F;&#x2F;www.math.columbia.edu&#x2F;~woit&#x2F;wordpress&#x2F;?p=8149" rel="nofollow">http:&#x2F;&#x2F;www.math.columbia.edu&#x2F;~woit&#x2F;wordpress&#x2F;?p=8149</a><p>[2] <a href="https:&#x2F;&#x2F;xkcd.com&#x2F;793&#x2F;" rel="nofollow">https:&#x2F;&#x2F;xkcd.com&#x2F;793&#x2F;</a>

What is the process by which &quot;samples&quot; are drawn from the population of intelligent beings? This is a keystone of the article&#x27;s argument, but it entirely hand-waved. It is not as if &quot;intelligences&quot; are created in the void and then assigned with some random distribution (uniform or otherwise) to bodies on planets-- each intelligent being in the universe is itself with probability 1.

A couple of weeks ago I read a more compelling theory, that also is an interesting solution for the Fermi Paradox. It said something like this IIRC:<p>The normal evolution of a civilisation of smart species is to arrive to a point where they experience an Intelligence Explosion [0]. (or how Elon Musk puts it: <i>Chances are we&#x27;re the biological boot loader for digital superintelligence</i>) [1].<p>In a cosmic scale, given the fact that the timespan to go from industrial&#x2F;high technology civilisation to a SuperAI is like a drop in the ocean (1000 or 2000 years), it&#x27;d be impossible to establish contact unless they co-exist at the same point of evolution, in the same (or near) star system, and in the same period of time.<p>Something far from probable...<p>I think that this is the most plausible solution for the Fermi Paradox, we haven&#x27;t been contacted by Aliens for the same reason that we haven&#x27;t &quot;contacted&quot; with ant colonies or microbes. We simply can&#x27;t, we&#x27;re in a different state of consciousness.<p>We are probably living among Aliens, but they&#x27;re too advanced for our reasoning and live in a different dimension&#x2F;cosmic state.<p>[0] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Intelligence_explosion" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Intelligence_explosion</a><p>[1] <a href="https:&#x2F;&#x2F;twitter.com&#x2F;elonmusk&#x2F;status&#x2F;496012177103663104" rel="nofollow">https:&#x2F;&#x2F;twitter.com&#x2F;elonmusk&#x2F;status&#x2F;496012177103663104</a>

Couldn&#x27;t a hypothetical Big Alien make exactly the same argument? There are plenty of exoplanets larger than Earth.

This article strikes me as a man who lives entirely inside a black and white room insisting that if he thinks hard enough, he can infer what colors in the world outside are like.<p>It is true though, that if you spin a black and white patterned disk, you will see colors.

This essay would benefit from making the particular anthropics used like the Self-Sampling Assumption explicit (and the paradoxical implications of it which leads to rejection by many) and explaining examples like the Doomsday Problem.

In &#x27;Solaris&#x27; by Lem the whole planet is an alien life form.

What is less worthwhile for a person to think about than the existence of aliens? Sure, solve world hunger, figure out inter-space travel, light-years distant communication mechanisms, prevent cancer, war, poverty.... Last I checked, aliens weren&#x27;t threatening the continuation of our species, or even leaving the lid up after a visit to the john for that matter.<p>How did this tinfoil-hat ridiculous article even make it into Hacker news!?

Why isn&#x27;t the conclusion &quot;our population size is the most frequent&quot; versus &quot;largest&quot;?

The idea of interplanetary species seems to invalidate this website in one fell swoop.

Wrong. We have no notion if we are more or less populas than other species, so we should assome that we are one of the many smaller (in number) by virtue of that being the more common, thus drawing the exact opposite conclusions.

Please, for all our eyes&#x27; sake, change the color of the font to something darker! Light-grey on white is just terrible.

I&#x27;m of the opinion that life doesn&#x27;t exist elsewhere. That said, I don&#x27;t care enough to even try to support my own bias. I&#x27;m not going to spend time trying to get anyone to believe either way, because we&#x27;ve got bigger issues right now. Aliens aren&#x27;t here, starvation is.<p>How did this ridiculous tinfoil-hat article even make it into Hacker News!?