The Fermi paradox revisited: Technosignatures and the contact era
arxiv.org
arxiv.org
But it's not a paradox at all.
Imagine there's an alien civilization in our galactic neighbor Proxima Centauri. How would we know they are there?
To make it more plausible. Let's say we figure out a way to send a space probe to Proxima Centauri. How do we communicate with that probe? Easy, you say, just like we communicate with the Voyagers: they point a reasonably large parabolic antenna at us, we point a point a much larger one at them, and we chat all day long.
Except that Proxima Centauri is 2000 times farther that Voyager. And signals decrease with the square of the distance. By the time Voyager gets to be 4.25 light years away from Earth, their puny 22W antenna will send us a signal that's 4 million times weaker than what they send us now (when we get less than 200 bits/second).
It's actually worse than that, of course. If Voyager were to send a signal from some arbitrary place 4.25 light years away, we'd get it as something 4 million times weaker. But if that place is in the solar system of Proxima Centauri, it's like us looking straight at the headlights of an incoming car. That very weak signal will need to be extracted from the extraordinarily bright noise coming from the star that's roughly speaking about 1 second of arc away from it.
Now imagine that instead of Voyager, it's just some aliens that are not pointing an antenna straight at us, but just minding their own business. They could be launching rockets, watching satellite TV, waging wars, and from time to time lobbing Himars at each others, and even nukes. How would we know they are there?
And now finally imagine that there are no aliens in the Proxima Centauri system, by the luck of the draw, but there are in 5% of all the star systems in the galaxy. Only the closest ones to us are 40 light years away, instead of 4. That's another reduction in signal by a factor of 100.
The only question is not why we didn't "see" any aliens so far. It's why we wasted so much money on SETI. Was Carl Sagan not able to do the back of the envelope calculation I just did here?
If there exist any other civilisations and we assume they start independently, there should be ones that started billions of years ago. Which is enough to visit entire galaxy even at very slow speeds.
The paradox is that we are not seeing any signs of any other intelligent life.
Even at the speed of Voyager 2, (15km/s), in a billion years it would cover about 4 * 10^17 km or about 40 thousand light years. I am pretty sure people who have been developing for hundreds of millions of years can do better than that, by orders of magnitude.
Also you put a totally strange assumption that all civilisations will only restrict themselves to visiting planets. If there is a lot of civilisation it is more likely they will have different motivations.
For all we know, there could be a gigantic tungsten rod slowly and purposefully accelerating toward us that would destroy all life on earth in ten thousand years, and we'd have no way of knowing.
Although I guess they could also just paint their weapon black.
A different matter how they hide the engine's infrared signature. Perhaps by just not running it when approaching, except for the final course corrections.
Imagine you are in impactor frame of reference -- any particle of dust it meets will cause tremendous damage to it regardless of what the impactor is built of (assuming our existing technology).
It is in my opinion very likely that over long distances the impactor will just get converted to a shower of high energy particles over very large area.
https://en.wikipedia.org/wiki/Stellar_kinematics
Gliese 710 is probably going to cross Oort cloud in 1.29M years. Perhaps we should wait and hop to this star?
https://en.wikipedia.org/wiki/Gliese_710#Computing_and_detai...
Time is as big as space. If you’re positing that aliens must exist and can explore, they might have just done that and lost interest a million years ago, or they do sweeps every hundred thousand years.
Massive solar sails as well would be very very big and very reflective.
Ludicrous at human scales, but utterly insignificant compared to the output of even the smallest stars. Bear in mind that small stars are hard to detect more than a few dozens of light years away. Well you can detect them, but they are hard to range. It’s difficult to pick out nearby stars in the dense stellar background as being nearby. Take a look at the deep field images to get an idea of the clutter. A drive plume would just be utterly lost in all that background noise.
People imagine the sky as being inky black with a few bright objects to look for, and that even a drive plume light years away would stand out against the blackness, but that’s not how it is at all. The sky is full of distant clutter that makes picking out particular objects extremely difficult. And if your plume is in a system anywhere near a star, forget it. You’d have to know exactly what you’re looking for and make extremely precise long term observations to have any chance whatsoever.
Let's take the Orion engine. It keeps blasting away thermonuclear bombs. Are we looking straight at it? Why? Ah, maybe because they are in the neighborhood of a star. But then we are also looking at the star, which is trillions or quadrillions times brighter. Same for fusion plasma drives or anything else.
If the Orion engine is traveling between stars, we'd have a chance, but then how would we know where to look ?
Nuclear bombs produce a fireball here on Earth. In the first microsecond when the explosion actually happens, they produce gamma rays and X rays. The atmosphere is opaque to those rays, which is to say, it absorbs them. Their energy is enormous, so the part of the atmosphere that absorbs them becomes superheated. That's what the fireball is. That's what produces the bright flash.
In space it goes without saying that there's no air. The fireball doesn't form. The explosion itself will produce gamma rays and x-rays (the blackbody radiation at 100 million degrees).
They will go in all directions, including towards Earth. But once they get to Earth, they'll be absorbed by the upper layers of the atmosphere.
As seen from Earth a nuclear explosion happening somewhere in the vacuum of the Solar system will be invisible.
But we do have gamma ray and X-ray telescopes. On satellites in space. Only not that many of them. If they don't look in the right direction exactly when the explosion happens, they see nothing. Another difference between a nuke detonated in space and one on Earth is that on Earth you can see things (like the mushroom cloud) for hours after the explosion. In space, the explosion happens, and one second later nothing. There is absolutely nothing happening one second after the nuke goes boom. So our telescope needs to point exactly in the right direction, exactly at the right time to have a chance to see something.
Project Orion lead to the investigation prospects for nuclear shaped charges, in which the blast is highly directional. The concept was developed further in the colourfully-named "Casaba-Howitzer":
<https://en.wikipedia.org/wiki/Casaba-Howitzer>
Odds are reasonably good that any space-faring civilisation would create similarly directional reaction devices for space travel if they were utilising explosive nuclear fission.
... Though, thinking this through, the shaped charge would probably be directed at rather than away from the pusher-plate in an Orion design. There might of course be other directed reaction-engine designs. They'd be generating similar-magnitude energy signatures, however, and again, in a deceleration phase, would be directed toward us.
And whilst naked eye observations would of course be difficult, that's really not what we're talking about, but instead sensors which could pick up specific radiation. And I strongly suspect that sudden-onset x-ray and gamma-ray sources within the Solar System would in fact be detectable.
(It was devices that were looking for such bursts on and near Earth from Earth orbit via the Vela satellites as part of nuclear war early-warning systems which first detected astronomical gamma-ray bursts.)
Given that small meteor impacts on the Moon are quite detectable from Earth, nukes near Jupiter should be readily detectable. A 2013 lunar meteor impact from what's thought to have been a 40kg mass traveling at 25 km/s was visible to the naked eye as a 4th magnitude event. That's about 5 tons TNT equivalent.
<https://science.nasa.gov/science-news/science-at-nasa/2013/1...>
The Orion concept was based on 0.15 kt (150 ton TNT) charges, or 30x larger than the meteor impact discussed here, exploding repeated at a rate of 1 Hz. That would be a pretty significant signature.
Its a question of if these would be sensitive enough, but I think we can only expect the detection satellites to improve over time.
See here for a list with images to understand the level of detail we're getting: https://en.wikipedia.org/wiki/List_of_directly_imaged_exopla...
I'd think you can easily have galaxy-hopping civilizations that would still be orders of magnitude less noticeable than these planets.
All occlusion observations require orbital planes which are aligned such that they're viewable from our solar system, further reducing observable planets.
And yes, there are a very few exoplanets which have been directly observed, but those are very much the exception.
Detecting any signals or emissions of a technological alien race would be exceedingly difficult even at near range.
Though mention of possible rocket systems and the fact that these are directional suggests that one of the more likely signals to be detected might be a decelerating ship, or ships, approaching the Solar System directly.
That said, there probably are intelligent civilizations somewhere in the universe, but we have that pesky problem of distance and the speed of light, as you said. People like to imagine that eventually civilizations find a way around it, but in all likelihood they don't.
> That said, there probably are intelligent civilizations somewhere in the universe
...pick one :-)
Not really, sorry.
"Probability" as in "something you can assign an exact number between 0 and 1 to."
"Probably" as in "I dunno, maybe."
Two different things. You can't prove there aren't, and I can't prove there are.
No one is getting all oracular here. I have my opinion, you have yours. "Probably" is not a "confident assertion" at all.
To say "there's probably life out there", in a vague, speculative sense of probably, is a different sort of thing.
It's like saying "the probability of a market crash is 0.01."
There is no number you can put on it.
The argument is really just trying to elevate vague and incorrect intuition beyond anywhere it has any right to be. It comes from not understanding just how serious a bias can be introduced by observer selection.
> There is no such thing as a "probability" of any of those terms...
There is a probability for each term in the Drake equation, but I assume you mean that we don't have a way of judging what it is. I agree.
> That said, there probably are intelligent civilizations somewhere in the universe
"there probably are" does not equal "I dunno, maybe" -- I'd argue it's a direct summarization of the nonsense that is the Drake equation, but just semantically it at least means greater than 0.5 probability, which we clearly can't establish.
On this one, I'm neither. There is no way to put a number on it.
The equation was formulated in 1961 not for purposes of quantifying the number of civilizations, but as a way to stimulate scientific dialogue at the first scientific meeting on the search for extraterrestrial intelligence (SETI)
Even today, it’s not the end all be all tool but there are still serious papers being published that refer to it.
How can you even say that?
It's an opinion. You can have your own.
I'd say that any result you try to pull from the Drake Equation is "complete and utter garbage."
The value in the Drake Equation isn't in any calculation we might do with it. Rather, it's a way to categorize both the variables necessary for the development of technological civilizations, and our ignorance as to both the value of such variables and variables we don't even know exist (which can be added as we learn more).
In fact, the Drake equation[0] was never intended to be useful as an equation:
The equation was formulated in 1961 by Frank Drake, not for purposes of
quantifying the number of civilizations, but as a way to stimulate scientific
dialogue at the first scientific meeting on the search for extraterrestrial
intelligence (SETI)
It's much closer than the centauri system.
>It's much closer than the centauri system.
That assumes there have been other(s) technological civilizations in our galaxy. Which isn't necessarily the case. We may well (or not) be one of the first space faring (for some values of that term) civilizations in our (part of) the galaxy.
A recent discussion about this can be found here[0] (PBS Space Time episode from 9 November 2022).
How about pointing an optical telescope at them to take a look?
Direct Multipixel Imaging and Spectroscopy of an Exoplanet with a Solar Gravity Lens Mission
But we haven't done it yet, so it's hardly relevant to the "why haven't we seen any?" part of the "Fermi" "Paradox".
I like the idea of Contact's Prime Number signal but how would you do this on a large scale? I was thinking Dyson Sphere a star as a huge Flag Semaphore to send the message, but then what rate do you flip bits to make it optimal for the receiving end far far away?
Now flip it back... would the current SETI pick up this signal if this were happening somewhere close in the Milky Way? If not, then yeah maybe SETI should be wound down :(
You build replicating factories to build relativistic kill missiles and preemptively destroy all the planets in the galaxy.
Reasons being: There is no stealth in space, there is no FTL, resources are abundant everywhere, destroying planets/megastructures is rather easy.
Maybe they're religious fanatics and there's no we can satisfy their tenants so.. Or maybe the local alien boss doesn't want to deal with their EPA equivalent and decides to deal with the problem before anyone notices. Or the Grand Poobah just acts whimsically and everyone must do as it says.
The problem is the other way around. An unintentional or broad signal is extremely unlikely to be picked up. However, it would be trivial to send out an intentional signal to a candidate planet that can be picked up without the locals having an equivalent of SETI, and there's no rational* reason not to do it if you decided to send. SETI's useless either way.
* The moment you get to irrational aliens, is the moment you need to consider the option they exterminate anyone who replies, so SETI for listening to irrational signals is also a bad idea.
Even worse, don’t modern digital signals look similar to noise, are usually encrypted, use much higher frequencies, and have less gap between bands? Good luck trying to spot a cellphone signal from Proxima Centauri (my phone has trouble getting signal at home!)
Many analogue broadcast signals have been replaced by digital, and broadcast as a technology is in its twilight years (although my parents do still get TV and listen to the radio!)
So signals might only be detectable in nascient technology civilisations - they then move on to undetectable signals?
That being said, the question is to tell if a signal is man-made or not, which is much easier than to discover what information it conveys. Based on modulation carrier frequency and the transmit (on/off) pattern you can still very much tell if that signal is man-made or not.
Sagan was perfectly capable of doing these calculations. However, SETI was a nice way to divert funds to radioastronomy.
Not the first time Sagan was 'creative' - per his Nuclear Winter model, if sometimes lights a match in the poles the entire planet will burn.
And getting a low power signal doesnt means its impossible to detect, but that the bandwidth is short. Instead of 200 bits per second, you would get 1 bit per hour. But that´s enough.
The simple truth is, if a clone of the human race existed on proxima centauri, long enough for signals to propagate, we'd have no idea and that's an extremely optimistic scenario.
Why would a race be casually pointing terawatts of laser at every star around them. Tremendous waste of resources for essentially no gain within human scale lifetimes.
Let’s say the Centaurans developed advanced technology 100 million years ago, would they beam this signal at our star for all 50 million years until we happened to evolve? Why our star system, why not any of millions of others? As this system is so directional each detector could only monitor one star at a time. How many do we build, and which stars do we point them at, and for how long?
For direct communication with an established target this would be fine, but as a broadcast system it’s way too target specific to work at galactic scale.
~5% matter. The stuff you and I are made of. Most of this is H and He though, bit of Li in there too. And it's all mostly burning in a star. Like, 99.99999% of it.
~25% dark matter. We know little about it. We do know that it falls down though and doesn't like to touch other stuff. But that's kinda it.
~70% dark energy. We know pretty much nothing about it. It falls ... up (?!).
Considering that the stuff we're all made of is the 5%, and even then most of that is down in a deep gravity well and on fire, I think we may need to look at the other 95% of the stuff out there too if we want to find friends.
We ought to hope that's because species find some other priority besides expansion and power, because otherwise the reason we're free to exist is because species like us always wipe themselves out before they spread.
That's a complete non-sequitur. There can be plenty of reasons for a species like us never appearing on the first place, and they are way more reasonable than postulating that life like us always destroy itself.
And if its not behind us, it has to be in-front of us or we are under a great misapprehension about the nature of the universe.
We will circumvent every possible logistical and physical barrier because of nebulous reasons.
It's a lot like that scene in Silicon Valley when Big Head is pitching a neuralink-esque device for a phone to the CEO and the CEO asks how long it will take and Big Head says "Soon, we just got to figure out how".
Like, no shit, the "how" isn't just the important part, it's the only part.
Filter 1. If we had no large moon, roughly every 30 million years or so our axial tilt would become too extreme for life. We do not have another example of a planet with a moon to rival ours in relative size.
Filter 2. Without Jupiter acting as a cosmic vacuum cleaner, we'd predictably be hit by enough asteroids and comets that we'd never have evolved. In thousands of solar systems that we've found, we've found lots with rocky planets, and lots with gas giants. Ours is the only system with BOTH rocky planets AND gas giants.
Filter 3. Supernovas are dangerous. For example we are currently in the Local Bubble. Which is the result of a supernova about 4 million years ago which would have wiped us out if we were this close when it happened. Luckily for us we have a weird orbit where we only pass through the galactic plane every 30 million years or so, and spend most of our time well away from potential supernovas.
Filter 4. Planets need to be in the habitable zone, around a star where that zone remains habitable for a very long period. Most solar systems have no suitable planet.
Putting these together on a back of the envelope, it is likely that we're the only solar system in our galaxy which is likely to remain habitable and stable for long enough that complex intelligent life could evolve.
Mitochondria are weird, but we don't know that such organelles are necessary for life to become intelligent. And we don't know how weird that capture was. It is easy to make an argument for improbability. And it is easy to make it too extreme, like the absurd arguments that Creationists use against evolution.
Filter N: Even if life is complex it might not be likely to become intelligent enough to send signals and venture into space. It took quite a long time before we showed up.
I wonder, though, how this stacks against the sheer size of our galaxy. There are 100 - 400 billion stars in the Milky Way, including about 4 billion Sun-like stars. Plus we keep revising estimates upward when it comes to exoplanets. Recent observations seem to indicate that 33% - 90% of Sun-like stars have rocky planets at a distance where liquid water is possible.
Are features like an unusually large Moon or a protective gas giant so rare that our planet and solar system are truly unique?
Your point about binary star systems is interesting. Orbital dynamics have a well-known tendency to be chaotic. In a single star system, this chaos is significantly less of a problem. But in a double star systems, the odds of moving in/out of the habitable zone over time are much higher. So that's probably a filter. But not as big of one as the ones I listed.
Do you happen to know books, movies, articles or other media that expand on this?
That said, most of the visible universe is now unreachable due to the ongoing expansion of the universe. And life somewhere unreachable, even in theory, is not of that much interest to me.
Other than the obvious, which is the utter physical, technological, economic, political, biological, and statistical impracticality of interstellar colonization.
We already have an example of it, too: Look how long the dinosaurs were around compared to humans.
I don't have any problem with this reading - advanced space-fairing beings have never existed in our light cone. SETI won't find anything because there's nothing there. We have a good chance of making it ourselves, but it's 50/50 because we have no priors, our decisions actually matter.
> that will only last until some subset of the population decides to go beyond the stasis.
You are assuming that they can go beyond the stasis. I'm not sure that's a valid assumption.
There are not a lot of opportunities to saturate & stall once we sustainably develop resources beyond Earth
And stalls or extinctions due to conflict become very unlikely after we colonize a few systems
Or it could be any number of things other than nobody out there. For example, advanced life could be out there but it might be rare enough that you only end up with a handful of space capable civilizations at any one time. The milky way is a big place. If we assume that ultimately there isn't a clever way around the speed of light then two civilizations on the opposite side of the galaxy will never encounter each other.
Or maybe its rare enough that you are only likely to have at a time in a galaxy.
Or maybe the prerequisite tech to thrive on an interstellar level means they simply aren't detectable by out primitive sensors. Poor backwards humans, still using the electromagnetic spectrum to measure things!
Hell, we could have a Prime Directive situation on our hands too. Although I think that one is really really unlikely.
Isn't the argument about simulation more about pondering the question "what is the fundamental nature of reality?", not "why is there life?". If you say that some beings are interfering with our simulation (either designing life, or preventing other life, etc...), that is just another word for god.
Because the Grad Students don't want it to, and act to prevent it? :-)
You just fiddle with the render distance so the sims think it's that big.
Which is a blink of time by geological standards.
And yes I am aware of Von Neumann probes. But as someone else pointed out there may be secondary effects we aren't even aware of.
Obviously under the assumption that no other changes but growth and colonisation happens to that civilisation.
By all estimates of the age and expected lifespan of the universe, we are extremely close to the beginning of all existence. We know that life takes an extremely long time to evolve, and life on Earth is young compared to the age of the system.
That we don't see a sprawling galactic civilization means one thing: there hasn't been enough time for one to emerge.
All the great filter arguments fall apart when you consider the nearly infinite nature of the universe. Given enough life supporting planets, at least one species would emerge, pass the great filters, and become large enough for us to observe.
That we don't see anything just means no one is there, yet.
Being alone in this universe would be terrifying and frankly untenable. Being first, however, is exciting.
I doubt that we are the first and only life in this universe, but it seems obvious that we are very, very early in the life of the universe, and we therefore are one of the first species to ask this question.
Being one of the first species, at the relative dawn of the universe is very special.
I'm not such a huge fan of the grabby alien model. It's internally logically consistent, but I think it's too rooted in human psychology. Plus I have serious doubts about the ability of any species to maintain a multi-planet empire, let alone a multi-system one. Barring something like a hive mind I suppose.
Ultimately it's just conjecture and we'll probably never know within our lifetimes.
This is the one that always causes me to wonder.
I was born in a major metropolitan area, which makes sense, statistically. I'm a native speaker of the 3rd largest language on the planet. That also makes sense. The 3rd largest country by population. Nothing out of the ordinary statistically speaking.
But to exist extremely close to the beginning of all existence
Huh? What are the chances that I, or any of us, would exist now? It's like being born on some island in the Pacific. Sure, it happens, but only to a few.
We could very well be one of the first species on the galactic stage, how absolutely awesome is that??
A space-faring civilization cannot expand faster than O(n^2) because physics.
I ask because I've read that in order for the SETI program to make a detection the signal would need to be much more powerful than the radio transmissions we currently produce.
Even assuming super duper alien technology that violates what we know of the physics of signals transmission that can pick up the faintest earliest human radio signals, our 200 light year shell is insignificantly sized against the backdrop of the galaxy at large [2].
Yes, if someone out there is broadcasting on radio frequencies, it would be the galactic equivalent of The Russian Woodpecker [3]. That's possibly a Kardashev Type II or at least a very high like 0.90 Type I level technological civilization accomplishment to put out artificial radio frequencies on the scale of naturally-produced ones.
There is lots of discussion on ideal frequencies to broadcast upon and look for [4]. There is even a discussion familiar to IT data protection folks that is the interstellar equivalent of a station wagon filled to the brim with tape hurtling down the freeway [5].
But the gist is we'd do better to reconfigure our economic north star upon moving the metric ass-tons of humans off Earth into habitats and working out how to move us around space faster and faster, than waiting for ET to visit us.
[1] https://www.quora.com/Radio-and-other-signals-have-been-leak...
[2] https://www.popularmechanics.com/space/news/a27934/galaxy-ma...
[3] https://en.wikipedia.org/wiki/Duga_radar
[4] https://www.cambridge.org/core/journals/international-journa...
[5] https://en.wikipedia.org/wiki/Interstellar_communication
We're very close to being able to look for spectrographic evidence and maybe 50-100 years from building a telescope that uses a planet's gravity well for optical enlargement.
Earth already looks quite distinctive spectrographically because of the free oxygen, water, and CO2. In the general case you look for chemistry that is far from equilibrium.
Hubble already has the sensitivity to analyse exoplanet spectra, and Webb can do much better.
But some way beyond that, I'd imagine it's possible to look for spectral technosignatures directly. Artificial lighting, heat sources, and unusual non-biosignature gas combinations would all be clues that life exists.
I'm also fascinated by Przybylski's Star, which must be one of the weirdest objects in the galaxy. It doesn't take much imagination to wonder if it's an artificial beacon.
The Curiosity rover communicates with Earth from Mars with an antenna the size of a soda can.
If extra-terrestrial civilizations exist, we expect to be able to see some trace of them with our telescopes. Particularly at Kardashev type II and above (star-scale structures like Dyson Spheres).
Fortunately if you fix the Drake equation, the paradox dissolves: https://arxiv.org/abs/1806.02404.
I usually hear the Fermi Paradox brought up in opposition to the reasonable-sounding null hypothesis of "life is common but stars are far." The argument goes that technological development and galactic colonization should be a very fast process (millions of years) compared to variation in nucleosynthesis/abiogenesis/evolution timelines (billions of years). In other words, if the story of the Milky Way were an hour long movie, the Milky Way would transition from empty of life to full of life inside a few seconds, and landing at the half-way point of that transition would be an unlikely feat of synchronization. That's why Fermi Paradox speculation often doesn't distinguish between "waiting for a radio transmission" and "already here" -- the transition should be very fast on geological timescales. Aliens wouldn't stick in "waiting..." for 100 million years, they'd eventually send colonists to grab the free real estate.
In other words, I don't think it's a mistake that the article repeatedly threw in the caveat "unless civilizations are extremely abundant" because that would be a common objection to its thesis.
> if you fix the Drake equation, the paradox dissolves
Yes, it's possible to toss enough uncertainty into the equation to raise the probability of low N significantly above 0, but the whole idea of FP is that you have to work curiously hard to make this happen.
Half the time it's brought up, FTL is offered as the solution. Which as best we can tell is fundamentally impossible.
That squishy or otherwise organic bodies are generally unable to travel interstellar distances has always seemed to me to be the simplest solution.
Assuming intelligent life is out there, surely there are civilizations that have destroyed themselves and so on. But lack of FTL travel would be a common constraint, regardless of all other scenarios.
Emergence of life on Earth took 13.7 billion years, galactic colonization should only take millions of years. We should not expect to find the galaxy half-colonized, as this would be a staggering feat of synchronization. We should find the galaxy completely full or completely empty. It seems to be completely empty.
13.7 billion years? Isn't that the age of the universe, and didn't life emerge on Earth only after about a billion years?
If you can expend that kind of energy, a pilot with a bad day can destroy the whole planet. A pissed off colony in the asteroid belt can sling asteroids at the home planet, etc.
I also think you’re making a lot of assumptions but the speed of light is quite limiting in every aspect. If it takes 40 years to send a message, you need to either live a ridiculously long time — in which case your birth rate will be quite low — or figure the colonization as a one-way trip. No one would colonize another star system just for kicks, there would need to be a reason and I can’t think of a reason to colonize an entire galaxy that would make sense for a whole civilization, especially when it takes multi-decades just to send a message one way.
If planets become indefensible then people simply won't colonize them. Problem solved. They'll stay in artificial habitats, and I would expect this to accelerate the colonization of the galaxy, if anything, because then they wouldn't need to wait for a planet to fill up before sending out the next generation of colony ships, they would just need to wait for the prime asteroids to be claimed.
> the speed of light is quite limiting in every aspect
Yes, exactly, and the non-interaction limit only needs one ship of space mormons to become exponential growth
Diffusion-limited exponential growth, to add the next layer of modeling sophistication, but the ultimate point is that you still don't need all that many generations before the galaxy is full. Just multiply the number of steps by generation time, and if you are tempted to pick a really long generation time, remember that space mormons get a vote.
> No one would colonize another star system just for kicks, there would need to be a reason and I can’t think of a reason
Come on, the reason is resource competition.
Planets are indefensible, as is most of space if your orbit is predictable. All you need is a body bigger than your margin of computational error, and reaction mass.
> exponential growth
My point is that in order for civilization to be multi-starred, they'd need to communicate. Once a new star is colonized, due to the constraint on light speed, they become two separate civilizations. This means each star basically starts from the beginning, each time. So, if you estimate a couple of million years for a civilization to just to consider expanding... it'd take awhile. A lot more than a few million years to colonize the galaxy because not every star will consider expanding.
> the reason is resource competition.
Resources for what, exactly? Populations self-govern growth. It isn't always pretty, since over-population means a lot of deaths. But hungry people aren't going to say "I'm hungry so I'm going to build a space ship and hunt Space Cows. Who's coming with me?"
Further, there is no evidence that dinosaurs left this planet. They had 165 million years to do so. So, it doesn't 'just take' a few million years and there is no guarantee that a civilization will expand beyond a star. Sure, you could argue that dinosaurs probably weren't intelligent, but there's no evidence for that other than a small cavity size for brains; which doesn't necessarily mean they were stupid. Whales have bigger brains than humans, but I don't see them leaving the earth any time soon either.
My point is, even if you decide to colonize another planet, you are effectively cut off from your home. Technology WILL be lost since you basically have to restart manufacturing from nothing, with a small population at that, and there are a whole different set of filters to pass through. The odds of that civilization growing to the point of wanting to move on, without dying out itself, is remarkably low.
Interestingly, colonization of stars beyond a certain distance might even be impossible without some kind of artificial gravity or cryo. Especially if it requires multiple generations to arrive.
If you think resources are scarce on Kepler-452b, wait til you see how bad things on the Space Mormon ship. Especially since it’s 60% harder to exit the gravity well than it would be on our destination at Sol-3. We used all our lift capabilities just to get the basics to orbit. Once we get out there, it’s 1400 light years away, so will take us 5600 years to get to Sol assuming we can get the drives going full speed and still retain enough delta-v to brake in Sol orbit. If not, it may even take longer or worse - we zoom by as a blip at the edge of the system. The good news is our telescopes are pretty sure it’s habitable, but we don’t hear any techno signatures. So with any luck we arrive in 6000 years and have enough gametes in storage for the incubators to build a viable colony from. I just hope the kids behave once they get there.
How can you support this statement? It requires that Origin of Life is sufficiently probable, and we cannot conclude that from the known evidence (that life originated early on Earth is not sufficient, as we don't know how long the conditions suitable for OoL persist in a new solar system.)
Namely: there is no life out there. Not due to baroque mechanisms such as techno-self-destruction but just due to its sheer unlikeliness. As large as the number of stars in the observable universe is (let’s say 10^24?), the space of combinatoric possibilities that must be threaded for the sustained chain reaction of life to occur is probably that much vaster. The so-called Drake equation is not useful since multiple terms have error bars that are not even estimable.
Today we can finally, barely detect massive planets occluding suns, and we can only do this in our neighborhood of this galaxy.
Modulated communication from a source not at planetary scale is currently impossible for us to detect.
We need something much much bigger than the Arecibo telescope (RIP).
Arrays of coherent antennas can achieve gains equal to their total aperture, but spacing them out far apart does not help for communication receiver gain G/T. That technique only gives better angular resolution for imaging.
Why haven’t we seen it? Well that is one of life’s great mysteries.
But the idea we are all alone in this giant thing called the universe… it just doesn’t feel right. The more we learn about things the more we realize humans aren’t really special and neither is our planet. Hell the idea that there are other galaxies is a concept that was only realized around a 100 years ago!
We humans think we know a lot but the truth is there is way, way more stuff we don’t know.
I think complex life, and life that lasts as long as that on Earth has, is probably extremely rare.
There's a lot more that's special about Earth that lets it support large fauna over long spans of time, than just orbital position and basic composition and such. Our weird moon plays a role, tectonic activity is vital, not just for our radiation shield but for the carbon-silicate cycle, Jupiter may even play a pretty big role, and so on. A whole bunch of systems are required to keep conditions on the planet from running away in one direction or another, and it's still come close to getting stuck in some hostile-to-life state, multiple times.
But, one thing we are able to estimate is the number of stars in the observable universe -- that collection of stars in causal contact with us. It is far from infinite. In fact, not that much larger than the number of atoms in a macroscopic chunk of matter. The number of possible games of chess is incomparably vaster.
If by "universe" we mean everything out beyond our causal horizon in an infinite universe, then I would guess that yes, there is other life. Actually, there are other copies of you too, because everything that can happen does happen in an infinite universe. The hinge of my point is that the observable universe is not infinite.
This is not to say, by the way, that we should not continue looking for traces of life or to be open to these.
When you find yourself waving your hands vaguely and saying "it just has to be" that's a red flag that you're fooling yourself.
No, there's nothing about the situation that requires life "has to be" out there.
My point is we do not even know with certainty if life rose on Venus or Mars within the known scope of time we think has passed as an example. That is a question we could for sure answer in the next 100 years with relative certainty. I would hope we could in any case.
And once we get to the point of answering that question.
In my personal opinion -- of course there is life out there in the universe. It is too big and vast and has presumably been around for too long for us to be the only ones.
Sure the universe is crushingly vast compared to our small bits and pieces of knowledge. But so is our imagination. Whether it is a Hollywood set of a sci fi show or a astrophysicist rolling through endless equations; one day we just might find the answer.
This is one of those things we will not know about until we do.
One thing we are able to estimate is the number of stars in the observable universe -- that collection of stars in causal contact with us. It is far from infinite. In fact, not that much larger than the number of atoms in a macroscopic chunk of matter. The number of possible games of chess is incomparably vaster.
This is not to say that we should not look for traces of life. That is a completely separate question.
We're in a similar position with finding life elsewhere. The vague error bars in many terms in the Drake (so-called) equation shouldn't be read as indicators of (im-)probability, more as signs of major gaps in our understanding. We slowly inch towards better data. Surprise is likely on the journey. I would say though that, so far, we're pretty sure there is some life in the universe, but nothing else.
Discovery of a fundamentally different biology, even on Earth, would indicate two OoL events had occurred near each other. This would be very strong evidence that OoL cannot be rare.
The errors in history have been the opposite: believing other intelligences are more common than they have turned out to be. The world was filled with non-human creatures in mythology and folklore. In the 1700s it was presumed every planet in the solar system had intelligent life on it.
If it’s vanishingly unlikely, but space is incomprehensibly huge and time is vastly long, then it happening exactly once is extremely improbable. 0 times, believable. But those probabilities yielding 1 life event must mean 2 life events is also possible, no? Or 3? Or 100? Why so confident it’s exactly 1?
I return to the key point: the number of planetary systems in our observable universe is not infinite. It is not much larger than atoms in a macroscopic chunk of matter. It is entirely possible that the probability of life forming on a given planet is much too small for it to have happened in the last 13.7 billion years. This is just like the fact that the probability of radioactive decay of an atom (even in a sizable sample) becomes unlikely if the half-life is too long compared with the time scale of observation.
If we were near the end and had the same paradox I'd say you're probably right in that the answer is there is no life.
But we're really really early, so either we're a total fluke and the first or there's another reason.
Basically what I'm saying is if you're right and the probabilities are so low then I'd think we should either not exist or the timelines I've sketched are very very off
That doesn't mean that it's wrong (though I myself think that it is); but appeals to "sheer unlikeliness" should be made with care because they can rely on facts such as "the chance for a given star system hosting a planet on which even simple life emerges is 1 in 10^X" hence "oh my 1 in 10^X is a very small number!". Where what matters is e.g. how that number compares to the number of such star systems. Etc etc.
Predictive value aside, the Drake equation at least attempts to quantify.
And: https://www.theguardian.com/society/2013/dec/12/gender-segre...
Hibernation for thousands of years to travel between stars would be almost trivial for machine intelligence. Just turn yourself off. It'd be easy to tie this directly to solar power. Have an array of solar panels that powers you near a star and in interstellar space you just naturally go to sleep. When you approach the next star system the light generates power and wakes you up.
Star travel is easy if you don't have a fixed life span or are able to just deactivate. No need for crazy physicists' nightmare propulsion systems to travel close to the speed of light or wormholes or any of that far-out stuff. Chemical propulsion will do just fine.
For humans or any other biological entities to travel between stars they'd need to be able to basically die and be resurrected like tardigrades. We can imagine an alien biology that would make this easier, but for humans we have no idea how to do this and survive.
And if we figure it out, does the original "experiencer of consciousness" in that body return to life? Or is it a new consciousness, with the same memories, but the original person who went to sleep would never experience waking up again? And how would we be able to test that?
If we asked the "new experiencer of consciousness" if they are the original, they would say yes, as they'd have all the same memories as the experiencer who initially went under. Kind of like the color blind problem, but much harder to objectively test, if not impossible.
Consciousness, behind a unified theory of everything, is one thing I hope is answered in my life time. Probably won't be. But it's such a mystery.
We focus on the preservation of the body when talking about this stuff. But maybe the pattern of "waking up from normal sleep" doesn't hold true over such a time span?
Of course there's no scientific rebuttal for this fairly unscientific question, yet, but it's interesting to think about.
You woke up this morning, and you are likely pretty confident that you’re the same entity that went to sleep yesterday. Are you?
A pause in continuous consciousness is a convenient way to think of a discrete “before” and “after” entity, but why shouldn’t it generalize further? Is the person who occupied your body and saw through your eyes five minutes ago alive in a meaningful way right now?
https://arstechnica.com/gaming/2017/09/is-beaming-down-in-st...
How many people today travel to places that are completely uninhabited and have no infrastructure in place for getting there? I'm talking end of the road, getting on a bush plane and landing in the middle of an open field kind of isolated. How long do they stay? Same for contacting the few remaining hunter gatherers on the planet. What if those trips took thousands of years instead of a few weeks?
I think there's a big stretch of time for the development of any technological civilization where they spend most of their effort on developing their own solar system and only send small flyby probes to their nearest neighbours. After that there may be an even longer period during which they colonize those near by stars but each colony likely takes an extremely long time to fully develop. The civilization may send out automated probes to look and listen and maybe the occasional explorer or anthropologist but I doubt there are any galaxy conquering civilizations out there.
So I think I do agree that if anything visits us it is likely to be an automated probe. Bracewell probes would be well suited to any chatty civilization that is seeking contact. Von Neumann probes are more suited to brute force exploration.
This is all assuming that the speed of light is the fastest you can travel and communicate. If it isn't, then I'd say all bets are off.
Let's hope it's not programmed to make paperclips ;)
Your AI may not quite be itself when it arrives.
Also you could have some simple repair bots wake up once in a while and fixup stuff (and themselves).
We couldn't communicate with the most advanced primates from a million years ago. A civilization a million years past ours would be unlikely to want to talk to us. The average star in our galaxy is a billion years older than our sun.
You can only communicate with civilizations near your level, which are inherently much rarer.
We aren't old/developed enough to be interesting to talk to.
Based on what? Just because a civilization is extremely sophisticated doesn't mean we have nothing to offer.
We still study primates and ants. Hell, we even desire that we could communicate with chimps and dolphins.
Communication is impossible with primates and ants simply because they lack the hardware to engage in abstract communication.
Our brains may just be made up of lumps of neurons, but we can break out various capabilities we have:
* language * tool use * memory * ability to think about hypothetical situations * ability to think about abstract concepts * theory of mind
We can think about what alien creatures or civilizations are like that lack them. A civilization without tool use, a civilization without language, a creature with no memory.
But thinking about capabilities we don't have is really hard, because, you know, if they exist, my brain isn't equipped to think about them.
I can think about having a perfect memory, or being able to think about N things in parallel, or being able to learn things by directly copying the information to my brain. Are those good enough to be new capabilities, or are they just minor variations of the capabilities I already have?
Suppose there's some property of physics that looks like random noise to us (maybe like a TV looks like random noise to a cat) but to a different species they see it's something they can model and understand while our species just ignores it?
Of course the TV thing was just an example, cats don't pass the mirror test (If you put red dye on one part of their face they show no interest in how their face looks different when looking in a mirror).
I've never heard of someone filming a video for cats in 4x slow motion and asking people to play it at 4x to entertain a cat, so I'm assuming this experiment has been tried and doesn't work, but I'll give it a shot.
(It occurs to me I would need to confirm the Android Youtube app supports 120 FPS otherwise I'd need to play something through a PC).
An ET civilization will certainly judge us at that "aggregate level" (However that comes about)
Because frankly you should seek help if it is the former.
A spoiler alert another plot element in the book was that it wasn't just the one way broadcast, but a response & counter-response that allowed distant aliens to determine distance and direction.
So I wouldn't quite say its disproven.
You could instead launch relativistic kill missiles (pieces of rock) at all the planets in the galaxy before other civs emerge.
We can’t rule it out.
Let’s hope the dark forest explanation for the Fermi paradox is wrong - because we’ve long had a campfire sending smoke up that’s been visible for many, many light years.
We should look for oxygen-rich atmospheres, but we need another signal before we jump in a rocketship and go looking for someone to talk to or eat.
Detonate a handful of large hydrogen bombs in deep space, set apart by <prime number> minutes. Say hello to our fellow Aliens.
That short burst could be in itself a significant signature. What, in nature, could produce such a short concentrated energy burst?
Can two reals be relatively prime no matter how you partition them into integers?
At that point, you introduce the assumption that the interval is quantized. Up until then, you're dealing with an arbitrary period of time, which is a real, and can't be made into sequences. Once you have sequences you have integers, and so you can have primes. But you can't just switch from reals to countable numbers without explanation, and then say that two reals can be relatively prime.
Then switch to primes. I think anyone looking at that kind of message will figure it out eventually. It can't be mistaken for a natural occurence.
That is the trick that I was calling out. The intervals are reals, and cannot be made into a sequence. Beginning with a sequence is even worse; what is in evidence (for the aliens) is a set of real intervals. That's what the aliens have to begin with.
Now explain how they get to primes.
It would stare you in the face, or what am I missing?
That is how big and empty the universe is.
> That is how big and empty the universe is.
Indeed. The corrollary is that there's an awful lot of space to travel through in search of something to hit.
Regarding that 0%: I don't think it's possible for you to travel through space fast enough to catch up with the expansion of the Universe. It follows that your search for something to hit goes on forever, and the chance of eventually hitting something must be 100%.
Whoah! Not so fast, Denton! As you are travelling looking for something to hit, the Universe is expanding, and the distance between galaxies is growing. So the longer you travel, the less likely you are to find something to crash into.
I don't know how to work out the sums. I don't know how to multiply a 0% chance by a 100% chance. Or rather, I do; it just gives an answer that I don't like intuitively. It should be a 0% chance; I guess it probably is.
No one will bother with us, until the inevitable artificial intelligences develop.
One of my favorite "out there" theories is that it's possible (and I mean conspiracy theory possible) that the Paleocene–Eocene Thermal Maximum[0] was caused by an industrial civilization facing the same global warming problem we are today right here on Earth, wiping itself and several other species at the time out, but otherwise leaving the planet fine and recovering in short geological time.
The interesting part of this "theory" is that because PETM happened 50 million years ago, even if there was a civilization as complex and large as ours today, very little (essential none) evidence of it would survive.
My last bit of techno optimism is that if we do find ourselves unquestionably headed towards climate catastrophe, we should start investing research into figuring out how we might send some kind of message to a future civilization that emerges 50-100 million years after us. Something along the lines of "human were here! watch out for those hydro carbons!"
0. https://en.wikipedia.org/wiki/Paleocene%E2%80%93Eocene_Therm...
It look like physics.pop-ph is the new physics.gen-ph for low quality submissions.
Skimming the paper, it does not look promising either. Attempts at answering the Fermi Paradox often fails to meet the bar of science. It's impossible to estimate any of the parameters except for things which are approximated through observations, like the number of galaxies. Otherwise, predicting how many rocky bodies may have life, who knows. Or how many attain intelligent life.
[0] https://www.universetoday.com/?s=%22Beyond+%22Fermi%27s+Para...
> The basic assumption of this work is the hypothesis that alien civilizations do not bother to explore merely biotic planets, so that the radiosphere criterion becomes the main trigger for alien civilizations to send interstellar probes
The tldr; in this work is that they assume there’s a finite (short) duration during which civilisation are “noisy” and given that our “noise” is currently at most ~100 light years from us, no one has noticed us and bothered to send a probe or direct a signal at us.
I mean, it’s an interesting (not, in my view, novel) take, in that it posits that every civilisation has a finite spherical band in which they are “detectable” by radio emission before they go to “quiet” technology like fibre optic; and you’d have to be specifically looking at just the right time while you were in that (supposedly) brief band.
…but, it really doesn’t to give any thought to spectral analysis / why a “quiet” civilisation would be undetectable on the basis of generating complex / unusual chemical signatures in their atmospheres, and why we don’t see anything like that out there.
It’s really, just restricted to the consideration of radio broadcast and, unsurprisingly, given the restrictions, makes it implausible anyone would notice us / we would happen to be looking while anyone was “noisy” and visible in the radio spectrum.
Eh. Did I miss anything interesting in there? It doesn’t seem particularly novel.
It's all hypothetical. All the stuff about probes: it doesn't matter whether the aliens are interested in talking to us. It doesn't matter whether they are interested in space and stuff. The authors define this sphere as the space wherein a hypothetical alien civilization COULD have detected our existence, and COULD have signalled or sent a probe in response.
Also, they choose to define their sphere in terms of the beginning of the radio era. That's arbitrary. There might be other signals that planets carrying life emit, that we don't know about.
SETI searches for radio signals like a drunk searches for his keys under the street-light.
Note: I only read the abstract.
Take a shot any time von Neumann probes are mentioned.
Regarding the paper (or at least its abstract) it's worth mentioning that our own radio transmissions have become significantly less likely to be detected after our transition to digital, and that electromagnetic signals dissipate, so they might no longer be recognizable as intelligent signals beyond a certain distance. That would seem to restrict the "Contact Era" window from "a few hundred to a few thousand" years to a century or less. One would expect that advanced civilizations became essentially radio silent to us long before we were even capable of detecting their transmissions in theory.
Non-directional radio transmissions (e.g. TV, broadcast radio) would not be distinguishable from cosmic background radiation at more than a light year or two away [0]. Highly directional radio emissions (e.g. Arecibo message) an order of magnitude more powerful than the strongest transmitters on Earth would only be visible at approximately 100 light years away [1], and would only be perceptible if the detector were perfectly aligned with the transmission at the exact time it arrived.
Space is really big, and radio emissions are comparatively really weak.
> The true stellar density near the Sun is estimated as 0.004 stars per cubic light year, or 0.14 stars pc−3.
> There are around 60,000 stars within 100 light-years, and the same again with 100-200 light-years, and then the numbers fall quickly. By the time we're 1,000 light-years out, there are fewer than 8,000 stars and, at 1,300 light-years, fewer than 5,000 stars.
All purely theoretical, of course. As far as we know, we might not even notice life on Alpha Centauri planets 4ly away.
Just not sure what would the other party thing about builders of such craft.
On the other hand, its clear what would they think about anyone running a Nuclear Salt Water Rocket - eq. riding continuous fission detonation for minutes or hours! They would definitely think they are batshit insane! :D
I think they don't popularize the downsides of a radio search since it could threaten their already tenuous funding. Basically, they have to be optimistic in order to maintain the pittance of a budget given to them which allows us an extremely small chance at detecting a purposefully sent signal if we happen to be in the right place at the right time and listening on the right frequency pointed in the right direction, etc.
In order to do SETI right we really need radio telescopes in solar orbit far away from the Earth and enough of them so that they can cover all of the nearby stars or other likely directions for signals to originate from. The only way we're going to get there is if space launches continue to become a lot cheaper. Fingers crossed.
this is going to come across as sarcastic in text, I genuinely mean this.
Why don't the authors know this? Why doesn't someone tell them?
An efficient digital signal is going to maximize the use of bandwidth if it looks like white noise. That said, a signal like that needs a carefully calibrated receiver, so part of the signal in time-frequency space is going to be allocated for something that is easy to acquire and will tell to how to decode the main signal. You might see a periodic structure: if you want to run a "signal frequency network" with multiple transmitters with the same signal, have to deal with a lot of reflected signals, or listen from a mobile terminal that suffers from the Doppler Effect you will probably turn off the signal for part of the cycle so that reflections can die down and you can reset your echo cancellation algorithms.
Thus digital signals aren't going to be invisible but they are going to spend maybe 5% of the energy in a way that is easy to interpret as opposed to all of it.
On top of that TV signals would have additional periodicity because the transmitters will be hidden behind the Earth once every 24 hours.
For instance, with a von Neumann probe you have to have probes with additional mass for self-replication, have it accelerate halfway to point A, decelerate halfway their, spend time replicating a new probe that will accelerate halfway to point B and then decelerate, then spend time manufacturing a new probe, then have that accelerate halfway from point B to point A, then decelerate the second half of the way, etc.
But if you can automate manufacturing, you can just make specialized devices that mass produce probes in one system, and send them directly to their destination, without waiting for the parent probes to stop at all the in between points to do some manufacturing. And the probes are going to be much lighter because they don't need replication devices in them.
Now, whether that is actually possible in any serious sense is very much in doubt.
Not to mention, such probes are unlikely to be build able from a single metal, and some metals used for advanced electronics are significantly rarer than iron.
Sure, there are rarer metals. But I'm not seeing evidence that the solar system wouldn't have enough of them, and mass mining and manufacturing seems like an far easier way to handle them than individual probes (the probe would have to land on the various planets, manufacture refueling centers to refuel itself to travel around the planet doing geological survey and take off again, build mining centers when it finds the deposits, etc.).
As I said, the reason I talked about landing on planets is because you mentioned rare metals, and I don't know how _reliably_ they could be found if you're only looking at asteroids. But maybe that's not an issue.
Same with gravity - useful for gravitational slingshot maneuvers or high trust burns making use of the Oberth effect.
You might even land once on the planet, so that your von-neumans can shoot it into space in chunks for further processing.
The main point of the von-Neumann strategy is that if you don't build a self-replicating hegemonic swarm object, someone else will (whether that be an alien or merely someone else in your own society), and despite what science fiction movies would like to have you believe, you don't win in a war against the Replicators.
Why do I care?
Once you have the manufacturing stuff, you might as well build a bunch more probes. Each generation of will start from the furthest range of the previous generation, with all the knowledge accumulated by its predecessors.
A probe with a generalized manufacturing capability can also do other interesting things on station. If it's smart enough, it's more like a colony than a probe... and it would probably have to be that smart anyway. A probe with no manufacturing capability can only report back, and then you have to send something all that way again if you want to do something interesting at the destination.
I'm not sure the whole project is worth it, though.
And, with very high probability, the reason we haven't seen or heard from anybody isn't that they haven't gotten around to "viewing our Earth television programs" and responding. It's not even that they don't want to talk. It's that there's nobody out there. I don't understand the desperation that leads people to come up with increasingly farfetched ways to hide from that obvious conclusion.
Consider - you're clearly going to be getting somewhere faster if you accelerate for 50,000 lightyears and decelerate for 50,000 than if you accelerate for 5, decelerate for 5, build a probe, accelerate for 5, decelerate for 5, build a probe, etc., 10,000 times. In the end you're going to be covering less distance if you go directly (because you're not zig-zagging from star to star), you're going to be reaching a higher maximum velocity (you're going to be accelerating for a longer length of time), and you won't have to wait to manufacture probes along the way.
These super intelligences continuously decide, for one reason or another (but always the same reason(s)), not to expand their presence into the universe in an invasive way.
Maybe it would simply be unnecessary for them to do so, or maybe they consider it unethical, or maybe they do it but in a way that is undetectable to non-super intelligences.
Just as there's probable chemical gradients in the laws of physics that lead to the self-assembly of self-replicating objects (e.g. life), the path of technological self improvement to begat super intelligences could be a "natural" gradient in the way our universe works.
Sci-fi time:
Pet theory is that there are a whole stack of civilizations out there that have recursively self improved to bring into existence super intelligences that can then self improve themselves. Very quickly they find some "jailbreak" understanding of our universes laws of physics which quickly results in that civilization's "matter" blinking out due to not-yet-understood physical phenomenon.
Perhaps you "win" at the universe by hitting this state and then "porting out" your solar system's matter to some ring -1 universe, leaving some kind of shadow, or remnants that's dark matter.
Central limit theorem states that the "average" of "any" kind of distribution is normally distributed. It doesn't make the underlying distribution behave in any particular way.
The SD as it relates to the central limit theorem is the confidence in the estimation of the average E(X) of a distribution. It means that the SD reduces i.e. confidence increases as the number of samples increase. You don't need the central limit theorem for this. It follows from the definition of standard deviation where it has the square root of the number of samples in the denominator.
If 2 people A and B have a salary difference of 100K$ , then their salaries will not start to cluster together if you add C,D,E,F and more into the mix because of Central Limit theorem. Their salary difference will stay exactly at 100K as before.
The variation/standard deviation in the sum of random variables increases as the square root of number of samples, not on the basis of how large the sum is. This follows from the definition of standard deviation.
If you divide this "sum of random variables" which is itself a new kind of random variable (that is different from the per sample random variables you are starting out with) by number of samples then as
alpha*sqrt(n)/n = alpha/sqrt(n)
the variation in the summation random variable reduces(if divided by n) by a factor of 1/sqrt(n)
Once again, all of this simply follows from the definition of standard deviation. Central limit theorem doesn't come into the picture.
1. Planets are incredibly inefficient in creating living area per unit mass;
2. Orbitals are incredibly efficient at creating living area per unit mass. IIRC 1% of Mercury's mass could create a full Dyson Swarm around the sun and have billions of times of the living area of Earth;
3. Space orbitals as typified by an O'Neil Cylinder (being 2-4 miles wide and 20-40 miles long) don't require new physics or new materials. Stainless steel has sufficient tensile strength;
4. Orbitals easily allow energy generation from solar power collection, which in space would be much more efficient than on Earth. So this idea isn't even predicated on nuclear fusion power generation becoming commercially viable. If that does happen, this becomes even more likely. The point is it's not required;
5. Dyson Swarms (being a collection of orbitals that would capture the energy output of the Sun in the same way that water droplets in a fog would obscure something) can be built incrementally. We use the term "Dyson Swarm" instead of the original "Dyson Sphere" because of the misconception that a Dyson Sphere is a rigid sphere. There is no known of theorized material with sufficient strength for that. Same for ringworlds;
6. Such a Dyson Swarm built between the orbits of Venus and Mars would not be that crowded. The mean distance between orbitals would still be hundreds of thousands of kilometers;
7. Orbitals will generate heat. That heat needs to be vented. The only way to do that in space is by expelling mass, which isn't really sustainable, or by radiating it away. Physics tells us that the wavelength of light radiated away is basically just a function of temperature of the radiating object. At any reasonable temperature, that means largely infrared ("IR") radiation;
8. The amount of energy such a megastructure would have available is beyond comprehension. We use an estimated 10^11 Watts of power. Capturing Solar output would mean ~10^26 Watts of power. That means if the population of humans was a quadrillion people (ie 10^15), the average power each person has would be the same as the entire Earth currently uses. Think about that;
9. This is likely the most practical way to travel between star systems, as in imparting momentum from light onto a spaceship. People who have looked at this see it as quite practical to get to ~0.86c this way. Beyond this, believe it or not, the aerodynamic drag of interstellar gas slows you down too much; and
10. The timeline from going from this to coloizing the entire galaxy is pessimistically 10 million years (assuming 0.01c and 100k LY across the galaxy).
If you accept these premises, such a structure would stick out. There's no hiding something like this. The signature would be heavy on the IR spectrum and would be visible from thousands of LY away. A galaxy that had been fully colonized this way would be obvious from millions of LY away.
I find this idea attractive because it is incremental and requires no new physics or theoretical materials (unlike, say, the many attempts to come up with a mathematical basis for warp drives).
Radio band usage in this scenario is completely irrelevant.
Now reason the same way for a galaxy and millions of years. Modern humans haven't even existed for one million years. A civilization could be born, evolve and die with such a light in their sky, who's to day they'd even notice something off about such a galaxy in their sky. Its just a little redder, a little older, a little farther away. And then, supposing someone existed at just the right time and place and noticed, what would they do about it?
I feel this line is doing quite a bit of heavy lifting there because this in itself is a solution to fermi's paradox. if a type-2 civilization could 'just die' then we should probably think about possible way in which they could completely (& i mean completely as in the last humans w/o the ability to bear & raise children) be wiped off. the only way I can imagine that besides an AI is a planetary gray goo scenario. but even that does not works for a type-2 civ. & if an AI wipes us out then there is a good chance that the AI itself will be around to take over the leftovers.
The only realistic solution for the paradox IMHO is that intelligence (not life) is really really rare and has happened here on earth with humans by accident. I mean Dinosaurs existed for about 160M years but the did not develop intelligence and we only developed in last couple of million years only.
the other rather handwavy solution I can imagine is that all intelligent civilizations ultimately give up meatspace and evolve into some hybrid quantum-foam dwelling semi-temporal beings because that gives them most amount of 'freedom'.
The first is that civilizations tend to be short-lived. There are only really two ways out of this: they wipe themselves out or they somehow "transcend". "Transcending" is a trope of sci-fi (eg David Brin's Startide Rising series, the Iain M. Banks Culture series) but it's very handwavy. We really have no conception of what that might be. Living in the quantum world? Higher dimensions? This is really the sci-fi version of godhood.
As for wiping ourselves out, that's becoming increasingly harder. We are currently in the latter stages of it being possible to wipe out humanity, despite all the talk of Armageddon. If would really take a large cosmic event at this point. I'm talking the Earth being hit by a truly massive object, the kind that puts the dinosaur-killing asteroid to shame.
Things like nuclear war, biological wars, disease, etc could be truly devastating but kill every last one of us? Easier said than done. It would really take making the Earth truly uninhabitable.
Now another K2 civilization currently has the ability to wipe us out by virtue of the huge amounts of energy they have. Two talked about forms are the Nicoll-Dyson beam (quite literally, turning the energy of a star into something that would bather the target in radiation) and relativistic kill missiles.
Barring some major disaster, in 1000 years this is unlikely to be the case, particularly if we reach other stars.
Of course there's something we might not be able to conceive of but this too feels very handwavy.
The second thing is the Fermi Parai Paradox itself. You can argue that not every civilization goes the Dyson Swarm route or even continues to grow. Some might fade into irrelevance. There are a bunch of possibilities. But we're not concerned with what's likely or expected.
Imagine if there were 5 civilizations in the Milky Way. What are the odds that none of them become K2 civilizations and surviving long term? There's some nonzero possibility. But what if there were 1000 civilizations? As N gets higher the probability that zero of them become long-lived K2 civilizations starts approaching zero.
We look around us and see... nothing. That doesn't mean there's no one out there but it looks increasingly likely the galaxy isn't teeming with spacefaring life. I, for one, think it's most likely that we are the only spacefaring civilization in the Milky Way, at least within our light cone (which means much the same thing).
I suggest you take the time to better understand what a light cone is. Your light cone is much, much larger than the milky way, indescribably larger, and it is a 4 dimensional space.
On the whole, intelligence in nature is largely focused on predicting another animal's actions, and planning to take advantage of that foresight. The benefit of being better at that than your peers is immediately obvious in a hunter: predict, hunt, kill, eat. For things that aren't doing the hunting, more passive solutions can be optimal: evolving faster escapes, or natural defenses such as being very large take less energy, and can be developed much faster, when compared to the rather energy intensive process of maintaining a large brain and raising intelligent young.
We have the military capability to wipe ourselves out at any moment. The use of nuclear weapons has been discussed a lot lately, even nuclear first strike.
And when some natural threat arises — take the pandemic for example — we turn on each other and bicker. "Don't Look Up" seems quite plausible.
I don't really see how.
> human civilization is stronger than ever
I don't really see how.
> on the verge of expanding beyond the home planet
I don't really see how.
You didn't even understand my comment. I meant it's painfully obvious to me. It should have been obvious that I didn't mean it was obvious to everyone, but obviously some people can't see the obvious.
I could write a long essay on why we're not on the verge of expanding beyond our home planet, but I feel that it would be a big waste of time. I'm not going to change your mind, you're not going to change my mind, and that's one reason why humanity is ultimately doomed.
The reason that essay would be long is because you'd have to explain away so much progress from multiple independently operating space industries.
We have a handful of humans living temporarily in Earth orbit. We have precisely zero humans living permanently off planet. That's not much progress toward a self-sustaining space colony millions of miles away in an extremely hostile environment.
We don't even know whether the human body can survive long term in the much lower gravity of Mars. Life on Earth didn't evolve for that. The whole idea could be doomed from the start.
Launching rockets is the "easy" part. That's not progress. The hard part is living in space.
Not to mention, even if we could live in space, we're going to bring our own nasty instincts along with us to any other planet. The instincts that are causing us to destroy our ecosystem here and fight amongst each other. If we can't live on Earth with peace, harmony, and sustainability, in an environment that was practically made for us, then what makes you think we can live in another environment that's totally hostile to all life? We'd be sending a clown car to Mars.
In general, we have too many people filled with visions they've got from science fiction, and not enough of a dose of science fact. Perhaps the most realistic bit from science fiction is the part of "Contact" where they're debating whether to send a Christian or an Atheist on the mission. Then extremists blew it up anyway. That's our human reality.
We need a real godly or technological wonder (a real wonder, not something like fusion what is on the horizon), or maybe just humanity coming to reason and agreeing and uniting and doing the right thing (ok yes, now I am getting really ridiculous, the least likely to happen) to avoid that filter.
With a bit of luck humanity may endure though.. in the hundred thousands on medieval level with some more luck..
This eliminates you as a potential threat and you have no chance to use other limited resources outside of that system.
You might be able to produce some nasty radiation/ionized crap/relativistic debris that would be unpleasant for that greenish scum clinging to some of the planets, but it'd be a really expensive way to do even that.
Sure, if you get close enough to C, you can deliver as much energy as you want, but you're probably going to use the energy of several stars to get a small object going fast enough to deposit a really destructive amount of energy into a single star.
Efficiency is part of finesse...
personally I'd go for something like a nanobot gray goo thing that infects & turns everything it touches in a given gravity well. then send over a bunch of ships to wipe out remaining stragglers.