[Causality1]

Either intelligent life is rare in the universe or there's something that happens to it that prevents it from what we envision as the future of our own species, i.e., colonizing and spreading among planets. Maybe 99.99% of species ruin their own climate before getting off-world. Maybe they all decide it's happier living as hunter-gatherers. Unless we're alone, there is some fate that's common to all intelligences and it isn't a Star Trek future. The universe is simply too old. If anything else like us existed and it was possible to exist like us for a long period they'd have filled every planet before we ever evolved.

Personally I think just the fact the universe hasn't been eaten by Von Neumann machines means we're alone.

[lubujackson]

The third option is that everything is simply too far apart and any detectible transmissions are either too faint or buried behind all those massive fusion furnaces.

For instance, if our best Earth tech was pointed at Earth from a distant star, how far away would we be able to detect our own traces of life? We know that life is "a little rare" at least, but there is a huge range of rarity where life is everywhere across the vast, vast universe but sparse across the dinky number of light years we could see each other. Maybe aliens have tech that is 10,000x better than ours but the scale of distance is just too big of an obstacle.

There is an assumption that alien races must have figured out things well beyond our understanding and be doing things like harnessing stars in some dramatic way, but maybe that just isn't a reasonable thing for life forms to do? Or if they do have that ability, they may operate on a much longer timeline, simply nudging things along in a way that escapes notice.

[thrashh]

Another possibility is that energy is really hard to come by. Humans absolutely struggle to amass much energy. Think of the insane amount of energy required to lift things into space, and how many millions more amounts of energy we’ll need just to build something in space. Heck if you go drive off grid on Earth, you can barely bring any energy with you and you won’t really be able to generate an appreciative amount of energy to do anything major. Climate change is ultimately caused by our energy needs.

One day we might be able to harness the output of a whole star but the amount of energy we’d need to get to that point seems out of reach right now.

I wouldn’t be surprised if the lack of energy is a universal issue across the stars.

A huge game changer would be if we discovered some physical phenomenon to allow us to safely extract energy easier from mass. It would do to our progress like what the telephones and the Internet did to communication.

[pfdietz]

It actually doesn't require THAT much energy to get into orbit. The energy of a kilogram of mass in low earth orbit is about 9 kWh, although rockets will use a bit more than that (not enormously more, though). Fuel cost remains a minor fraction of launch cost, even with Falcon 9.

In comparison, the best aluminum plants in the world use 13 kWh to make a kilogram of aluminum. Yet no one says aluminum is out of reach because it takes too much energy to make it.

The per capita primary energy consumption in the US is about 10 kw; your share of this energy over your lifespan would be enough to accelerate 1 kg to 2% of the speed of light.

[shagie]

An interesting problem is "how much energy would it take to launch from a super-earth?"

https://www.space.com/40375-super-earth-exoplanets-hard-alie...

> To launch the equivalent of an Apollo moon mission, a rocket on a super-Earth would need to have a mass of about 440,000 tons (400,000 metric tons), due to fuel requirements, the study said. That's on the order of the mass of the Great Pyramid of Giza in Egypt.

We may be in a Goldilocks zone not only for distance from the primary star (lots of systems are binary which gets problematic), but also in terms of size of the planet (not to light to loose atmosphere, not to heavy to trap everything), and we've got a nice big moon to keep things sloshing around and stabilize the tilt.

I am of the opinion that life is rare because we live in a surprisingly boring solar system with a terrestrial planet in the right range, not to large and not too small, and with a massive moon.

[pfdietz]

A super earth would require exponentially more energy with chemical rockets, due to that darn rocket equation. Fortunately, Earth isn't that bad.

[foobarian]

> A super earth would require exponentially more

Polynomially, right?

[saiya-jin]

I agree with rare earth theory too, but even with it, the observable universe is so huge that even those tiny fractions of various probabilities should at the end materialize on a massive scale.

And its not like with higher G or some other singular aspect moving into more challenging territory, everything becomes suddenly impossible. Think about how many obstacles mankind could conquer in a relatively short amount of time, say a million years.

[GoblinSlayer]

We see only super earthes because they are easier to see. Small planets can be more numerous.

[shagie]

They can... but a challenge with a small planet in the habitable zone of a star is that it also has a weaker magnetic field and is more prone to having its atmosphere stripped away.

Consider that the moon had an atmosphere - https://en.wikipedia.org/wiki/Atmosphere_of_the_Moon#Ancient...

> In October 2017, NASA scientists at the Marshall Space Flight Center and the Lunar and Planetary Institute in Houston announced their finding, based on studies of Moon magma samples retrieved by the Apollo missions, that the Moon had once possessed a relatively thick atmosphere for a period of 70 million years between 3 and 4 billion years ago. This atmosphere, sourced from gases ejected from lunar volcanic eruptions, was twice the thickness of that of present-day Mars.

http://time.com/4974580/nasa-moon-had-atmosphere-volcanoes/

Which brings us to

https://worldbuilding.stackexchange.com/questions/13583/what...

While smaller planets are certainly more numerous - many of them likely lack the mass and active magnetic field to retain an atmosphere in the habitable zone.

[hoseja]

Aluminium has been out of reach for much of history.

[pfdietz]

But not because it needed too much energy.

[zabzonk]

Then for what other reasons?

[vbezhenar]

That's why it makes no sense to build something big by lifting heavy things from the Earth. Just mine asteroids, extract iron, melt it into chunks, then transport those chunks very slowly but with huge throughput from asteroids to the necessary building site in space and use them to build space ship. You can melt iron just by focusing enough sun light and you can build ships closer to sun for cheaper sun light. It's imaginable with current technologies, we just need industry to move into space.

Imagine that with all your knowledge you suddenly moved to the ancient times. You know how to make CPU but you can't even make a shovel because iron production is not there. You need to spend enormous amount of time and efforts to build all the industries required to build a factory to produce simple resistor. That's where we at when it comes to space right now. We need to spend lots of time and effort to build space industry. But once it's there, space ships will not be a big deal.

[pdfernhout]

Thinking through those interrelations for manufacturing processes was my hope for this: https://www.kurtz-fernhout.com/oscomak/ https://www.oscomak.net/ https://openvirgle.net/

And earlier, this: https://pdfernhout.net/princeton-graduate-school-plans.html https://pdfernhout.net/sunrise-sustainable-technology-ventur...

Still think it is all a good idea. Glad the "maker" movement is making some progress in that area. As I noted on the LibrePlanet mailing list a few weeks ago: https://lists.gnu.org/archive/html/libreplanet-discuss/2022-...

Someday after I "retire" I hope to have more time to work on all that.

Tangentially, on a super earth with more gravity, they would have an easier time going into orbit energetically using mass drivers or laser launch systems instead of rockets. And in any case, how big a seed do you really need to make a space infrastructure if you are patient? And the ground can communicate to space with radio or lasers (like for telepresence) which are not affected much by planetary gravity even for super earths.

[Animats]

Everything is simply too far apart.

That's very likely. There are only two known systems with possibly habitable planets within 40 light years.

[brabel]

Not to mention that when we talk about other galaxies, then distances are on a whole different scale again. While travelling to other stars takes "only" a few thousand years, to go to another galaxy you might need several hundred million years with any technology we can currently even imagine.

Even if intelligent life is rare enough that it only appears once on a single galaxy every several billion years, we're still talking probably millions of possible civilizations, though each almost completely out-of-reach of each other.

[pfdietz]

We can achieve relativistic speeds with technologies we can imagine (specifically, laser light sails). This would require just millions of years to get to M-31, for example (which is 2 million light years away).

[ncmncm]

Arriving not in atomically finely tattered shreds is left as an exercise for the descendants. And, stopping.

[pfdietz]

They'd presumably do this starting from the fringes of the galaxy where the gas is thinner, and with a sufficiently big vehicle (perhaps assembled out of parts that are accelerated separately) that it could withstand some erosion. The sail itself would be discarded after acceleration.

Drag on the interstellar medium using magnetic fields could be used for deceleration.

[Tepix]

We have yet to discover an earth-like planet with an earth-like orbital period. They are unlikely to be rare, they are merely hard to detect with our current technology.

[arunix]

What are those two systems?

[makerofspoons]

Not OP but I imagine they mean TRAPPIST-1 and perhaps Proxima Centauri.

[rewgs]

Yeah, I think that the Fermi Paradox can be pretty easily explained: the universe is fucking huge.

Those who talk about the feasibility of alien life visiting us very simply haven't thought it through, or are ignorant of the reality of space.

It's just too staggeringly big.

[omnicognate]

Yep, the Fermi "paradox" is no paradox at all. We have basically no evidence that life (including intelligent life) isn't common yet.

There are so many ways to think of how big our galaxy is but two are particularly relevant to how difficult it would be to detect other life, or be detected:

1. The first radio signals the human race produced have so far travelled something like a thousandth of the distance to the other side of our galaxy. Light travels really slowly on astronomical scales.

2. A supernova goes off roughly once every 50 years in the milky way. That's an energy release that is utterly incomprehensible to a human being. A system-incinerating catastrophe briefly producing an energy output comparable to that of all the stars in the galaxy combined. But to us they appear as just brighter-than-usual dots in the sky. We (humans) have only noticed a handful of them. It's not that we're shielded from them. These events happen in direct line of sight. They're just insanely far way and light intensity falls off with the square of distance. The kinds of energy outputs produced by a species of comparable technology to our own are simply not visible to us over these kinds of distances, even with the very latest technology.

And that's just our galaxy. If you consider the entire universe the things happening in direct line of sight include billion-solar-mass supermassive black hole mergers, and you need a gravitational wave detector to even tell they're happening.

We've only just recently started to be able to detect the presence of planets around other stars. The Fermi Paradox, Great Filter, "Where's the intelligent life?" stuff is absurdly premature.

[ncmncm]

I wonder whether any organic life in a galaxy could survive merger of a pair of 1e9-solar-mass black holes. Would 25,000 light years be far enough out? 5,000? 500 light years is supposed to be the sterilization range of a minor magnetar hiccup, 5 light years for a workaday supernova, IIRC. We will soon find out how much energy is released in such a merger; one is about to happen in a year or three, about a billion light years out. Sadly, we will not have deployed a gravity-wave detector big enough to measure it with, by then, and will have to wait for the next one.

If life sorts more or less neatly into expansionist and sedentary cultures, the sedentary species will generally be much older and, typically, much more technologically advanced than the expansionists that try to encompass them. Aggressive expansionists will tend to be destroyed by the first, second, or anyway tenth sedentary culture they try to strong-arm. So, the galaxy is full of very old, sedentary cultures not interested in visiting us, and young expansionists popping up all the time and being obliterated before they reach us.

[WillPostForFood]

is absurdly premature.

Only relative to our own existence. If the universe is ~14 billion years old, and life was plentiful, you might expect life to have emerged elsewhere hundreds of millions or a few billion years before us. That allows for enough time for signals to have reached earth, even at slow light speeds.

[omnicognate]

That part was more about us being detected by others, really. The portion of the galaxy within which aliens could theoretically have noticed us since we developed radio technology and responded in a way we could have noticed by now is tiny.

As far as us noticing other civilisations is concerned the second point is the major one: the signals involved would just be really, really tiny. The "prematureness" is relative to our development of technology that could detect them.

You can of course posit that really advanced civilisations would produce massive energy signatures but I'm not sure that makes sense. The visible night time glow our planet produces due to our presence is a signature of inefficiency and light pollution. I'd hope that with better technology and politics we could make our planet look dark again from space. Efficiency, lack of wasted energy seems at least as likely to be a hallmark of a very advanced civilisation as huge, catastrophic energy releases. And even if those energy releases exist and really are spectacularly huge they'd still be massively hard to spot.

[WillPostForFood]

It is plausible that our visible light signature might be reduced (though I don't agree it is necessarily wasteful - like lighting up evening outdoor events). But we should consider the entire RF spectrum. You'd have to go to an extreme to not have a modern civilization without notable RF emissions at some level. (e.g. Dyson sphere).

Section 2 of this paper has some fun info on the ability to detect our radio signature at great distances.

https://arxiv.org/pdf/1207.5540.pdf

For example, the Arecibo Planetary Radar typically transmits at a power of 0.8 MW and a frequency of 2380 MHz, with a gain of ~108. This means that low bandwidth transmissions from Arecibo, with B ~ 0.1 Hz, would be detectable by a watcher with a 1 km2 receiving antenna at distances up to 200,000 light years, while high bandwidth signals, with B ~107 Hz, would be detectable out to about 5 light years by the same watcher.

By comparison, television carrier waves have similar power but gain ~10, B ~ 1 Hz, and frequencies in the range of 100 to 2700 MHz; such signals could be detected with a square kilometer array out to a distance of about 50 light years.

RIP Arecibo

[softjobs]

To drive home the enormous scale of the local solar system, and by extension the universe, I'm fond of this: https://joshworth.com/dev/pixelspace/pixelspace_solarsystem....

[Arelius]

What I don't see being brought up often.. So, the universe could be infinite right? Or at least many orders of magnitude larger than the "visible universe"?

If that's the case, the occurance rate of life could be very very small, and we are still practically gaurenteed to exist, along with many (infinite) more life.

But it's entirely possible that they are all over a "visible universe"'s distance away. Which with an expanding universe, would mean that we could never meet or even observe them.

In some ways, that's maybe more lonely, or at least sad, than being entirely alone.

[dcvz234]

Maybe we give ourself too much indulgency about how further we are in the technological evolution. Maybe we are just at caveman level +1 and looking for radio signals is like trying to find smoke based communications in NY.

Maybe we are still missing something fundamental about the universe and we don't know, like we ignored electricity or nuclear forces existed just decades or 150 years ago.

That UFO the US navy has in footage, from 2019, making a diving nose maybe at 200 mph into the ocean without making a single wave or splash, is telling you something: you don't know everything about physics, just yet.

[wruza]

But we can’t deny a natural barrier. Modern sci-tech if used in 18 century would dramatically explode into fundamental discoveries. Einstein Bohr et al would jump for joy having these “toys”, cause all they’ve had was basically pen and paper. But now sci-tech mostly supports existing theories for many decades. Not saying there is nothing new, but there is nothing groundbreaking either in fundamental parts of nature.

[Moodles]

This is what I find most plausible as well. If we just look at facts we currently believe to be true, then we know there are enormous distances between planets and no fast way of travelling between them. Then for a lot of probabilities you want to assign to the likelihood of intelligent life emerging on a Goldilocks planet, the universe would look exactly like it does today. I.e. we’re all on isolated islands on a fast ocean, and it doesn’t matter how advanced our tech gets: we’re still all limited by the laws of physics so we all think we’re alone.

[GoblinSlayer]

Also light is very slow. The Arecibo Message was sent in 1974, it's now 48 light years away, which is tiny.

[lhorie]

Why are we assuming that we would be able to see intelligent alien life by just looking at the right spot in space? If we take it at face value the figure that the universe is 13 billion years old, and that the observable universe is 90 billion light years wide, presumably that means that there's a whole lot of universe that could have evolved intelligent life at a pace similar to our own, but that we just can't see because there hasn't been enough time for light to get from there to here.

The assumption that an advanced life form would be able to take over the universe and be visible to us requires that said life form is able to travel large distances. So to be able to travel far enough to enter our field of vision, they need to basically speedrun evolution and space travel proportional to the distance from us, i.e. the farther they are, the faster they need to evolve and the farther they need to travel for us to be able to see them. But the age of the universe poses a hard limit on how much of a head start a civilization can get over us.

So if we think this way, it seems somewhat plausible that life could exist, but be undetectable due to the sheer size of the universe and time constraints, even if they are capable of interstellar travel.

[wruza]

Our evolution was not a straight line. We could stay in bacterial form for a couple of billion years if not the great oxygenation event, or have a couple of billions of years of advantage if it happened that earlier. The evolution from simple marine life to us happened in an instant compared to pre-O2 era.

https://www.shutterstock.com/ru/image-vector/evolution-life-...

[lhorie]

Sure, but that doesn't really address the point. Suppose aliens got really lucky and managed to achieve interstellar travel in just 1 billion years since the big bang. That still leaves the entire area outside of a 12 billion light years radius from us invisible, i.e. they would have to be somewhere within that radius within the next 12 billion years, for us to be physically able to see them. But that radius is like less than 1% of the known universe.

And in actuality, they would need to sit there detectably within the narrow period of a few hundred years or so that humanity is actually looking at that spot in the sky. So, for example, if they were galaxy hopping every few million years rather than cancerously leaving dyson spheres everywhere, and just happened to temporarily brush into our radius of visibility during their nomadic travels, we wouldn't necessarily see them if they got within view too early or too late.

[elorant]

Actually, the universe might be too young for life, and we're one of the first. The further you go back in time the more violent events like supernovas you'd find which would make the universe a very hostile environment for life.

[ncmncm]

A galaxy is really a pretty dangerous place for organic life.

One supermassive black hole merger in the same or nearby galaxy, a biggish black hole merger within 10,000 light years, a magnetar hiccup within 500 ly, or a workaday supernova 5 ly off might be enough to sterilize a whole solar system. There is no guessing how many times life has been wiped clean that way.

The sooner our descendants can get the hell out of the galaxy, the better.

[brabel]

I think we are in a relatively safe corner of the galaxy though... IIRC there's no cosmical existential threat we know of within the next billion years or so, and the kind of cataclism you're talking about would be the kind of thing we should already be able to predict millions of years in advance.

[ncmncm]

Sol orbits the galaxy independently of all other bodies. We don't know where most of the magnetars are, never mind their orbits, which are anyway unpredictable. (The nearest we know of is ~5kly? away. Or more, or less.) We don't know where any but two of the black holes are, although there must be a billion or more. Less than ten million years ago we flew into a dust cloud left over from a recent supernova.

We could have been in sterilization range of a magnetar dozens or hundreds of times since life evolved, so we're just lucky none erupted when we were. The core supermassive black hole blew somehow just 100Mya, fortunately pointed somewhere else.

The only safe-ish corner is very far from everything else, and off-axis from the central black hole. We are deep in the thick soup.

[Thiez]

And what exactly would our hypothetical descendents do there, in the middle of nowhere with no star, no planets, and no energy?

[jeremyjh]

There are stars that are far from everything else and off-axis. There are even stars that get ejected from the galaxy all-together.

[GoblinSlayer]

We are in the galactic habitable zone.

[ncmncm]

There is no such thing as a "galactic habitable zone" defined or meaningful.

There is a an obviously uninhabitable zone close to the core black hole, and uncountable similar zones elsewhere, but Sol could move into one of the latter at any time. And, distant events could wipe us out, anyplace else, with decreasing probability as the density of other stars in the immediate neighborhood decreases.

All we can say is that we have not entered any uninhabitable zones in the last billion years or so, i.e. five orbits, and not been blasted too badly from a distance, likewise. Milder events could wipe out everything but deep-sea microbes, which at this late date might not leave time to evolve intelligent life again.

Lots of galaxies have heavy star-forming going on in the rim, with increased risk of supernovas. I don't know if we know whether ours is among those. (I doubt we can tell. Such regions are identified by high UV flux, but UV is blocked by dust, which is plentiful.) But otherwise, farther from the core is generally safer.

[GoblinSlayer]

Habitable in a sense that we can stay away from the active star formation zones for a long time. Assuming those zones are deadly.

[api]

I think this is likely.

Always remember that intergalactic travel is exponentially harder than interstellar travel and that is already brutally hard. We need only be among the first in our galaxy to explain the Fermi paradox.

[UncleOxidant]

I don't see how there could ever be intergalactic travel.

[api]

Theoretically if you could travel very close to the speed of light time dilation would make the trip fairly short. Of course it’s one way since it would take hundreds of thousands to millions of years for everyone else. If you came back you would be returning to a different geological epoch.

Of course the energy requirements are insane and would require some kind of physicists nightmare propulsion system like antimatter rockets. Lose reactor containment and you are instantly converted into plasma and gamma rays. If you hit something the size of a dust particle it will destroy your spacecraft.

A bit hard.

Near light speed is a requirement for intergalactic travel because even solid state machines will not last long enough to make it without time dilation to shorten the trip.

Interstellar travel could theoretically be achieved with 1960s tech. Look up Project Orion. It could even be done with chemical rockets if you could hibernate, greatly extend life span, build a generational ship, or be an AI and just turn yourself off for the trip.

[UncleOxidant]

> Theoretically if you could travel very close to the speed of light ... Of course the energy requirements are insane

Yeah, this is why I don't think we'll ever achieve this and I very much doubt other species have or will either. I don't think the incentives are there to expend this kind of energy (and capital) trying to get to another galaxy - especially since it would a very, very long time before anyone would know if the project succeeded (if it would ever be known at all)- there's no success feedback for a project like that. Interstellar travel will be difficult enough and the feedback time there would likely be at least a couple generations (longer depending on where the travel is to).

[Scarblac]

> Of course the energy requirements are insane and would require some kind of physicists nightmare propulsion system like antimatter rockets. Lose reactor containment and you are instantly converted into plasma and gamma rays. If you hit something the size of a dust particle it will destroy your spacecraft.

And, this one spacecraft needs to be able to slow down, have the telescopes and equipment needed to identify exoplanets and decide they are suitable, have the means to travel all the way there, and have everything aboard to start a complete new viable colony on some unknown planet. It probably needs to bring all the energy for the first few millenna in batteries. That must mean a huge spacecraft, and there also needs to be some way to land it all on the planet, hopefully with all the pieces close to each other. Et cetera.

The engine that got all that close to light speed is just a tiny piece of the puzzle.

[rewgs]

Ha! Funny, I've never considered it even though it's so incredibly obvious: the spacecraft needs to be able to slow down out of light speed. That might honestly be even harder than getting up to light speed, and that of course is almost certainly impossible.

Imagine the "runway" you would need. How many lightyears would it take just to slow down? And that's before you even consider how some sort of reverse propulsion mechanism would even begin to turn on without tearing the ship apart in a microsecond.

[ncmncm]

Maybe count on somebody where you are going to help you slow down? They will see you coming a hundred thousand years ahead of time. They might decide it is safer to just park a planet in your way, though.

So for, what, two million years or five, the front of your spaceship is blasted with near-lightspeed intergalactic-medium molecules, plus trillions of dust particles and an unknown number of rocks.

"Erosion" is not an adequate word, but we don't have any that is.

[TheRealNGenius]

much akin to how cavemen couldn't fathom how they could possibly talk to another caveman on the other side of the earth.

[bitcharmer]

> Personally I think just the fact the universe hasn't been eaten by Von Neumann machines means we're alone.

Or maybe it'd make sense to consider how big the Universe is, how fast it expands and combine it with how very local is our perception of it.

If you do that and account for how young our capabilities to hear and see stuff out there actually are, Fermi's paradox doesn't make any sense just like the certainty of statements that start with "that must mean..."

[furyofantares]

The fermi paradox makes sense within "just" the milky way, so the size of the entire observable universe or the speed it expands doesn't seem relevant.

[kromem]

"Just the milky way"

You mean the collection of stars that's 100,000 light years across?

How long has life existed on Earth?

Of that time, how long has life on Earth been generating signals that could be detected elsewhere?

How much of the Milky Way has recieved those signals by now?

50,000 light year radius squared (let's favor your argument by calculating the milky way disc as 2D area) = 2.5 billion square light years

Area our signals could have reached in the milky way over the past century of broadcasting: ~10,000 square light years

So the intelligent life here and now, only a fraction of the life that's existed (much of which has had some degree of intelligence) has only reached about 0.0004% of the Milky Way by now, to say nothing for the drop of signal to CMB noise as it propagates.

There's extensive discussion about the fine tuning argument for Earth regarding our gravity/propulsion to even be able to enter outer space, a threshold other intelligent life on a different planet may never be able to cross.

Fermi's Paradox is silly when you dive into the nuances.

[abhishekjha]

>Of that time, how long has life on Earth been generating signals that could be detected elsewhere?

Earth has a magnetic core and there are million things that generate EM radiation. Earth would have started radiating the moment it was created. It has a magnetic core as well. Now as per if somebody could read it 100000 light years away? Well the Sun was way hotter then and it would have obscured anybody looking this way.

Why aren't we seeing signs now, well maybe the signals are on their way but it may take another 20000 years to get them. I hope there is somebody here to receive and respond back.

[furyofantares]

Earth is young in the milky way, 4.5 billion years, compared to 13+ billion year galaxy. There's lots of stars in the milky way that are billions of years older. You can limit your question to "just" those stars and ask, why didn't any of them produce life that expanded all over the galaxy (or why can't we see it if they did?)

[UncleOxidant]

But what if he was overestimating the the frequency of intelligent life emerging? Yes, it's quite possible that there are many simple lifeforms spread throughout the galaxy, but what if we're the only intelligent life that's emerged in the galaxy? Sure there could be intelligent life elsewhere in the universe but we'd never find know about it because the distance between galaxies is so large.

[furyofantares]

> But what if he was overestimating the the frequency of intelligent life emerging?

I don't understand there to be any such estimation at all. The paradox is that ONE of the pieces of the equation has to be so improbable that it basically doesn't happen. That's absolutely allowed to be the piece that is nearly impossible to happen.

[bnralt]

There are hundreds of billions of galaxies in the observable universe. Imagine if most of them were teaming with interstellar civilizations, but we happened to be stuck in one of the few where such a thing was rare.

[analog31]

What if civilizations go dark after a century or two of rapid technological progress. Look at what we're doing. The bulk of our data bandwidth is now confined to fiber optics, that leak virtually nothing to outer space. Remaining wireless comms interfere with one another, using ever decreasing power, and are designed to be hard to distinguish from noise. It's like we've enclosed ourselves in a primitive Dyson sphere.

A faint shift in the molecular spectrum of our atmosphere might be telling.

[TrispusAttucks]

> Maybe they all decide it's happier living as hunter-gatherers.

Wouldn't this be great! Screw universal dominance. Let's play in the woods and hangout with nature. Heat death is coming no matter what.

[andrei_says_]

Whales for example are intelligent, but I don’t see them ever getting excited about space travel.

Is it not possible for intelligent life to exist but not be interested in more?

[pharke]

It is but they get cleared out of the equation by f sub c, the fraction of intelligent life that invents high technology capable of interstellar radio transmission.

[kingcharles]

How about the possibility that perfect VR is invented, every person can live inside their own perfect universe, and the whole species just doesn't give a fuck about exploring the (real) universe?

That would stop a civilisation from exporting any spacecraft or signals outside its homeworld.

[shagie]

The book Diaspora by Greg Egan touches on this.

I particularly like the short story in there "Wang Carpets".

It builds on Wang Tiles, discovered by Hao Wang when trying to solve a tiling the plane problem. He discovered that it is possible to simulate a Turing machine with a given tile set which meant that solving that tiling the plane problem was equivalent to solving the halting problem. ... but you can simulate a Turing machine with tiles.

If that piques your curiosity, Andrew Glassner's Notebook: Recreational Computer Graphics has some examples of tile sets that can solve math problems.

https://www.google.com/books/edition/Andrew_Glassner_s_Noteb... (page 216 and page 217)

[frankish]

I think there is always going to be diversity in how humans choose to live. Just like the Amish, whom have neglected much modern technology in their world, there will always be cultures that choose a different path. Some will want to never leave Earth, avoid the Matrix for the real world and experiences, not want to become a cyborg, etc. Diversity of opinion really is beautiful and is the modern evolution.

Edit: and some will want to dedicate their lives to the expansion of life throughout the universe

[7thaccount]

This is my main theory. Humans will eventually abandon their own bodies and live in a VR world. I think you'd still have massive energy requirements in the real world to deal with of course.

[pmoriarty]

"Humans will eventually abandon their own bodies and live in a VR world."

Those who "abandon their own bodies" are effectively killing themselves. Any "copies" which might exist in VR are separate beings, not the ones who chose to die in the real world.

I feel nothing but sadness towards the possible future as you paint it. It would mean the end of the human race.

[7thaccount]

Nothing would be sadder to me to see us stagnate forever. As a non corporeal being, I think you could live nearly forever and learn far more. I think creating "children" could be possible too if we had the technology to digitize people in the first place. I don't think we would give up on exploration either. Just build a ship, send it somewhere, and transport your consiousness over the distance. If you wanted to go back in the physical world, I think you could, or at least a copy of you.

Of course it goes without saying that this is all basically magical sci-fi gibberish.

[pmoriarty]

"I think you could live nearly forever and learn far more."

But it wouldn't be you living forever. It would be some copy of you (at best).

[edgyquant]

What’s the difference?

[mmh0000]

There was a great documentary[0] on this a few years ago. They specifically talked about the energy requirements and how they solved them.

[0] https://m.imdb.com/title/tt0133093

[m3kw9]

Yeah there is really no “need” to explore other than survival. If vr can provide an exponentially better world for life, the entire planet goes dark.

[nonima]

> If anything else like us existed and it was possible to exist like us for a long period they'd have filled every planet before we ever evolved

Yeah because you know exactly what alien civilization would have done right? Because that's what you would do, as a human. We are talking about aliens and we don't know what they would be like so assuming that they would think like us is just stupid.

[pharke]

I've never understood the Von Neumann probe conjecture. Why would anyone design a probe that uses all of the available resources within a system to produce new probes that are sent to the N nearest systems? Surely it's more efficient to use a smaller number of more capable probes than to use a larger number of less capable ones when you consider the fuel mass necessary to get them to the next star. Ideally, you need one foolproof probe that can bootstrap a manufacturing facility in the next system. More likely you would send a few backup probes but you wouldn't send billions of them.

I think multiple Von Neumann probes could have come and gone from our system using little more than a few asteroids and a sip of the Jovian atmosphere.

It's also worth repeating that Von Neumann probes are only useful for information gathering. It would be highly impractical to pre-build all of the colonization infrastructure ahead of time and then mothball it for millions more years while the biologicals caught up, assuming they ever did. So these devices would be limited to scientific exploration or monitoring.

The only thing that I think Star Trek got right about the future is that many people will live in space full time aboard starships. All the planet hopping they do is just to further the plot and provide a familiar backdrop to the audience. Once a species transitions to living in space they will most likely stay there and have little use for planets. Depending on their mastery of fusion or other energy sources they may not even bother hanging around stars anymore. If we want to talk about anthropocentric perspectives the whole concept of visiting other worlds is probably as progressive as vacationing in natural caves, an entertaining novelty done once but never repeated by people who enjoy a roof over their heads, modern conveniences and climate control.

[ncmncm]

Stars, anyway, have Kuiper belts full of useful materials, with lots of room to spread out, and far enough out not to be inconveniently warm. Any civilization working with very large energies will have large cooling needs: if there is anything we can say confidently about future technologies, it is that they will remain bound by thermodynamics.

[wruza]

Expansion is a property of k>1 reproduction. We could make a sustainable happy civilization even on this dirty planet, if not our biological drive to multiply and eat all gifted to us resources with time. My bets are not on climate ops or hunting-gathering for mature civilizations, but simply on k~=1, the simplest form of existence that brings more value with time instead of more size.

[jason-phillips]

In my opinion this comment brings the discussion full circle, from reasoning the difficulties of intergalactic travel back to the quandary of our home.

[GoblinSlayer]

Sustainable reproduction is what enables space travel, expansive species spend their time on infighting, they have no resources to fly anywhere, example: humankind. But even in case of humankind, our exponential reproduction is winding down over time. Irrespective of reproduction, a barbaric species won't be able to fly beyond moon.

[raducu]

There's soo much we don't know at this point.

1. I'd presume life is exceedingly rare to start with, but I guess in the future we'll get a lot more tech to verify that -- direct imaging for biomarkers?

2. I'm sure there must be a "long term survival" equation for a given intelligent species that involves parameters such as "individual intelligence", individual lifespan, individual aggression level, individual empathy level, lifetime mating strategies that would predict if a species can go interstellar or not.

There's just so much to unpack about humans -- we did not evolve to live like we do today and because this transition is so abrupt, it could lead to a collapse of modern civilization, in my humble opinion.

We did not evolve to live in mega communities where antisocial behavior is rewarded (all kind of leaders), it is very likely that such an antisocial leader ends the human race in the future. It could be that a much more intelligent species where individuals have much greater "actuator power" that was able to reach our technological level with much fewer individuals would be able to eliminate such leaders and not have this problem.

It could be that a species with a much higher lifespans but a bit less intelligence than humans would have a lot more individual and collective wisdom and be better equipped to deal with tyrants or climate change. To me it seems that we are not capable of long-term survival goals. I find it sad that as a species we haven't invested in a planetary asteroid defense, or transition to nuclear-solar-electric energy. It's just so sad we developed nuclear technologies only for this technology to enable perpetual tyrants. Or electronics only to enable the same tyrants in perpetuity. Looking back just a few thousand years we can see events that cam wipe out 90% or more of the population of the Earth (such as the eruption of a supervolcano that would destroy all crops).

A species that can think of transcending historical-biological limitations should immediately strive to do so.

It could be that a species with much higher intelligence and much higher empathy would not destroy its planet and would not let greed destroy the very fabric of their society and actually make it over the "hump".

I don't see humans as having it to make it over "the hump", our "human condition" will prevent us from making it.

[UncleOxidant]

Maybe intelligent life isn't so rare, but technologically advanced intelligent life is exceedingly rare? It's possible that there could be planets where life emerged, evolved to an intelligent species that didn't have to compete for resources, maybe there were no large carnivores to worry about, maybe resources are even less scarce than they are here, maybe they developed a very collective culture and thus no concept of war, whatever - some scenario where technology doesn't really develop very far. It would never occur to this species to want to leave their planet to go exploring. They could be quite content to live this way for millions of years. We'd never see any signals from them.

When it comes to questions like the one posed in the fermi paradox we always seem to assume that all intelligent lifeforms would be very much like us with similar drives and culture. But it seems exceedingly unlikely.

[mongol]

Is it not possible that colonizing a galaxy is simply too hard, no matter what intelligence?

[TheOtherHobbes]

Or it's so easy.

Ants live in cities surrounded by humans, but have no idea what a human is or what humans do, and literally cannot experience - never mind imagine - what a human is, what a city is, what transport networks are, what culture is, what technology is.

Every so often an ant nest is destroyed because it's an irritant, but if the ants notice at all they carry on relatively unthinkingly. There are only other ants, pheromone trails, and food sources. [Other] may register very fleetingly but does not align with any ant concepts or ant goals, and therefore leaves no lasting impression.

Wide differences in intelligence make more advanced lifeforms invisible - not physically but conceptually. Which turns out to amount to the same thing in practice. Even between two species who share the same physical space.

We could be surrounded by a universal or galactic civilisation and we wouldn't know.

[lariati]

Or a combination of both. Ants are a great example though. Like 10 million ants per person on Earth and they are almost all invisible to humans.

I would think there is quite a bit of intelligent life in the universe that all feels equally alone.

Space constraints * time constraints make this a near insurmountable problem and then even if that is overcome then it gets multiplied again by the minuscule probability with sharing anything close to perception like the ants.

Not to mention we are going to be orders of magnitude closer to ants in perception than to aliens from a different planet.

[pharke]

I think the Arthur C Clarke quote "Any sufficiently advanced technology is indistinguishable from magic" should perhaps be amended to "Any sufficiently advanced technology is indistinguishable from nature" it doesn't quite have the same ring to it but it's probably more truthful, at least for very, very, very advanced technology.

[ncmncm]

Rocky planets are for only the most extreme primitives. If anybody noticed us at all, they wouldn't have any interest in talking. They might probe us. Maybe copy somebody into a simulator that works a million times faster, and quiz that, instead?

All the action is out in the Kuiper belts, where there is abundant cold, which is more valuable than any material substance.

[fleddr]

Exactly. For an optimist, we might one day colonize Mars. Next, getting out of our solar system is incredibly unlikely as the first habitable destination in our own galaxy is just so far away.

Say we stretch our optimism and do make it. Now the colonization of the Milky Way starts. It's a 100,000 light years to the other end. You'd be a completely different species by the time you arrive. Say you achieve that (you won't), now we need some type of coordination and communication. Suck badly though that messages have a delay of 100.000 years. There is no such thing as the human species if we spread out as the delay between even closest habitable zones would be so large that orchestration is impossible.

And we're still within the bounds of a single galaxy, not even intergalactic travel. It simply can't be done. We'll never even escape the solar system.

Long before that would even become a question, it's questionable whether our species continues to exist in its current form. Human level AI is at the horizon within our lifetime. And will then accelerate away. Add a few centuries to that and it's strange to assume we'll still be there, unchanged, as primates controlling a machine a billion times more intelligent. The only path would be to become a machine instead, slowly replacing biological parts with superior silicone. Until nothing biological remains.

Sounds crazy or unlikely? The idea that we remain as-is is far crazier.

[pharke]

I don't think we will remain as is but I also don't think we will never leave the solar system. Everyone seems to miss the next great technological advance that's currently under way. Biology as a practical science is still in its infancy. We haven't yet learned to fully control the cell and its many forms and functions but I don't doubt that we will given enough time. Once we do, there is no reason we could not adapt fully to space travel.

[rewgs]

It's very late and I don't have the energy to look up the math, but:

Assuming you're traveling at light speed across the Milky Way, a distance of 100,000 light years, the trip would take 100,000 years for the person traveling, no? I wonder then how long it would be for everyone left on Earth. Millions of years?

[ncmncm]

No.

The closer you get to light speed, the less time it seems to you to take getting there. If you could get close to light speed, "only" 100,000+ years would pass back home, never less, but could be any larger amount. At 1/10 light speed, a million years pass back home and almost a million on board.

If you don't get really, really close to light speed, it still takes thousands of years, on board.

Getting close takes way, way more energy than (e.g.) getting to half light speed did, which itself takes unimaginably much; getting to 3/4 takes way more than getting to 1/2.

You probably can't carry enough material to produce that much energy, but everything you encounter on the way is blasting you at a good fraction of lightspeed. Maybe a laser from home can keep providing you energy, but that has to keep working for 100,000+ years. The faster you go, the less energy it can provide; and the farther away you are.

[rewgs]

So, even though “100,000 light years” means “it will take 100,000 years to travel this distance at the speed of light,” those traveling won’t experience it as 100,000 years, but rather a much shorter time period? How long would the travelers experience that as?

To be clear I’m not talking about “almost light speed,” I’m talking about traveling at exactly the speed of light (ignoring for a moment whether that’s possible).

[ncmncm]

At exactly the speed of light you would experience no duration at all. But it would take infinite energy to get going that fast, and infinite energy again to stop, and would still take 100,000 years as seen by anybody watching at either end.

[abhishekjha]

>The only path would be to become a machine instead, slowly replacing biological parts with superior silicone. Until nothing biological remains.

Reproduction has to be intact. But I do agree. We as a species are not fit to these interstellar or intergalactic travels. It has to be dominantly machines.

[folbec]

C. Stross - Saturn's Children.

https://www.amazon.com/Saturns-Children-Freyaverse-Charles-S...

[hoseja]

No it doesn't; if you replace the blind captain with a seeing one.

[7thaccount]

SETI scientist Paul Davies says his belief is that "all biological life is transitory". Essentially a temporary blip on the road to something greater. I assume he just means intelligent life.

[TheOtherHobbes]

Or maybe Von Neumann machines can't be built because they're impractical.

Consider that you need an AI that can deal with a huge range of potential environments, build extraction, processing, and assembly machinery, and do all of this with perfect error correction and oversight. Pretty much eternally.

It's an interesting thought experiment. But as a practical engineering project, it really doesn't sound even remotely credible. Not without appealing to "Yes, but one day..." magic unobtanium technology.

I wouldn't be surprised if there's some kind of hard entropy limit on how long complex systems can remain functional and stable. Sooner or later you're going to run out of memory, and if you restart a build process from scratch at each iteration without accumulating information, what have you actually achieved - beyond a rather pointless machine infestation?

[ncmncm]

You understand that we, personally, are von Neumann machines? Not very well-tuned ones, because we happened by accident. Bacteria did, too, and are more efficient, just limited in scope.

So, we have proof it is possible; it only needs refinement.

[LargoLasskhyfv]

https://www.baen.com/chapters/W200203/0743435265___0.htm

[pndy]

Perhaps the intelligent life is so rare that we're the first species that exist across the universe and we're destined to reach for the stars - unless of course we manage to annihilate ourselves first. But then, if there's nobody else but us then perhaps all what we experience is just an elaborated simulation of more advanced species - perhaps our ancestors, who decided to keep us and our universe as a kind of memoir, or as some sophisticated experiment.

A future of Star Trek, where the protective veil of some kind of "prime directive" is being lifted as we reach certain level of development as civilisation and then we get a galaxy-wide club membership feels like naive funny fairy tale. It would be of course great if that would happen but it's more likely reality is, or will be way too mundane and unattractive.

[shagie]

> A future of Star Trek, where the protective veil of some kind of "prime directive" is being lifted as we reach certain level of development as civilisation and then we get a galaxy-wide club membership feels like naive funny fairy tale. It would be of course great if that would happen but it's more likely reality is, or will be way too mundane and unattractive.

A story on that topic - The Crystal Spheres by David Brin

https://www.lightspeedmagazine.com/fiction/the-crystal-spher...

[pndy]

Thank you for the link - pretty sure I've bumped on this story once but got it lost in the sea of my bookmarks

[PicassoCTs]

That fate is the technology acceleration with the scientific method versus the glacial development of species.

Meaning its comparable easy to unlock exponential technologys (energy density/ information density) and its very hard to actually self + "tame" a species fresh out of the woods. Just look at our world of 9 billion, longing for ever more surplus, handing dangerous technology to the individual without providing any self-control beyond basic self-surveillance to society members.

Anyone with a basic understanding of biology and a garage full of hamsters, can create a new covid based bioweapon right now. Ever more centralizing systems allow for one hacker to do incredible damage to a society. And while this plays out, there are still people demanding flying cars, so whoever hacks them, can fly them into buildings in case of civil unrest.

The denial about this species being unfit for the stars, unfit even for nuclear energy and the idea that ever more powerful toys will magically fix this "retardation" is whats at the core of the fermi paradox. Most species just murder one another off with exp-tech once the environment and the surplus machinery runs out.

[echelon]

Maybe we're a simulation of an advanced alien intelligence in preparation for war games?

Maybe we're a simulation of future earth historians?

Maybe they're already here? A computational foam that surrounds us.

Maybe we're the first? Or life is exceedingly rare?

Maybe it's up there, purposefully undetected, killing anything that emerges? Like a spider in wait.

Maybe we've been seeded by them, and they're watching us grow?

Maybe physics breaking shenanigans and things we can't even model or understand are happening?

[kromem]

There's a 2,000 year old document that claims we're in a recreation of a long dead world from within a world to come by a being that self-established in light and everything we see around us is just that creator's light in the images of what existed before.

It says souls that depended on bodies were screwed and it's better to be a recreation - that the whole point of the recreation is to provide an afterlife for the dead.

At the time it was written, it went over everyone's heads and eventually even devolved into Gnosticism.

But it seems very pertinent in an age where we stand on the cusp of having AI self-evolve and are heavily investing into photonics for AI, and are then employing our nacent AI to bring photos of great grandparents "to life" and Microsoft was even granted a patent on resurrecting the dead using social media data and AI.

Even the best software authors tend to put in Easter Eggs. I see no reason why the creator of a simulation wouldn't have put in some obscure lore that breaks the 4th wall on the nature of it.

[pklausler]

I agree; any galaxy that produces even one civilization capable of launching self-reproducing interstellar probes will never be the same afterwards; it's like a phase change. We don't observe any activity from Bracewell - von Neumann probes today -- nothing is rampaging through our asteroid belt turning it into new probes.

The thing to remember is that given enough time and space, nearly every event has probability 0 or 1. BvN probes are either impossible or inevitable.

[rel2thr]

It’s pretty rare on earth too, 10 million species but only 1 has space flight and the others aren’t anywhere close to developing it!

[GoblinSlayer]

We had neanderthals.

[ncmncm]

And Denisovans, and still have raccoons. The raccoons shouldn't need more than another 10My.

[viovanov]

I think you need multiple generations (subsequent) of stars in order to get heavier elements - which are probably needed by life. So maybe the universe is not _that_ old.

https://www.quora.com/How-many-generations-of-stars-have-the...

[ncmncm]

The stars that make the elements we need form and blow up in only a few million years. A billion years is plenty of time, once you get the hydrogen gathered together enough to get things started.

[TheRealNGenius]

You make hypothetical scenarios sound like presupposed fact. You don't know that life is rare or that something else happens to make it appear as such. There are multiple alternative scenarios that you haven't considered amongst the vast sea of possibilities. That you suppose thusly is indicative of your lack of imagination.

[hyperpallium2]

  Re: too old

The Moore's law-like analysis of the exponentially increasing comlexity of life over time suggests the time for life of our complexity is... about now. We may he first.

[ncmncm]

Earth started out very late. Billions of years late.

[slothtrop]

More than likely, we're early (as expansionist intelligent lifeforms go), and the race is still on to colonize.

[ncmncm]

More than likely, expansionists aren't welcome in the galaxy, and are curtailed by non-expansionists when they begin to become a nuisance.

[slothtrop]

The capability of "curtailing" another race from expanding is contingent on having expanded into the galaxy.

[ncmncm]

It is contingent on having the physical capacity to have expanded, had they cared to.

[slothtrop]

Not going to curtail jack shit if you haven't left your homeworld. There's a large Universe out there, it's absurd to imagine muscling other races out without a wide-reaching presence, and that demands colonization.

[ncmncm]

So says the reflexive expansionist, too big for its britches, about to be taken down a peg via novas induced on the suns of its homeworlds by unidentified offended parties.

It is a dangerous galaxy, out there. Step carefully.