The Fermi paradox is good for a nice chat at a party.
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?
We've been able to fly or emit radio signals only for a bit more than 100 years.
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.
Only if they are in our own Solar system. But you can easily imagine a supercivilization visiting lots of solar systems, but not establishing permanent colonies everywhere. As I said, what if 5% of the solar systems are teaming with life? That would still be tens of millions of solar systems in our galaxy. The diversity of life could be something to make Star Wars look unimaginative. And we'd have no idea they are out there.
What kind of argument is this "only if they are in our own solar system"?
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.
If the dark forest hypothesis is true, you can bet any civilization advanced enough to detect us will go out of their way to avoid being detected by us.
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.
I am not sure about usefulness of kinetic impactors at near light speeds over long distances.
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.
Presumably because it's high density and thus higher destructiveness vs detectability?
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.
Stars move relative to each other. You won't need much higher speeds than what we can already achieve, as long as you're willing to wait for another star to move nearby.
If they visited us a billion years ago, would we know?
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.
Plot twist: dinosaurs were really an alien species. After they were wiped out by an asteroid slung at the earth by an evil prince, the earth was written off as a memorial site.
>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?
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.
Well said. The "Drake Equation" is complete and utter garbage. There is no such thing as a "probability" of any of those terms, in the way we normally understand probability, i.e. dice or card games.
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.
>Well said. The "Drake Equation" is complete and utter garbage. There is no such thing as a "probability" of any of those terms, in the way we normally understand probability, i.e. dice or card games.
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)
First, I was gently poking fun, not seriously criticizing. But since this is apparently that sort of conversation: no.
> 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.
Even then, he is putting bounds on probabilities. Specifically, that the chance that life arises around a random star is >> 1/(number of stars in visible universe).
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.
"Bullshit", as I use the term, is misrepresentation of the state of your knowledge by confident assertions you can't back up with evidence. The statement is precisely that, bullshit.
If you mean the world is divided into frequentists and Bayesians, you're right. I think most people who throw around the Drake Equation are frequentists.
On this one, I'm neither. There is no way to put a number on it.
It seems to have been pretty successful at its intended purpose:
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.
Your calculation is likely wrong. See, you can build a laser in a spectrum not generally emitted by stars, and point directly to another star system. You dont need much power, yes, perhaps some terawatts, but it can be pulsed, total energy would be low.
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.
OP is saying how would we detect a civilisation unknown to us, and for who we are also unknown. A system such as you describe would only be practical for a civilisation trying to communicate with a known counter-party. Otherwise which stars do you target your laser on, and for how long?
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.
All beams will broaden and distort though. No matter the wavelength or pulsing, anything made by not-a-pulsar is likely to get garbled and shifted beyond comprehension. You can fix this with some really really big fancy lenses, maaaaaybe. But you'd have to know the distance of the point you're trying to image the laser onto first. Collimated light over those distances just isn't ever going to stay that way.
Just want to point out the currently known composition of the universe:
~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.
Dark matter appears to be a very weakly interacting fluid, completely unsuitable for developing any kind of structure at the local level. Dark energy is, well, energy. Also incapable of local structure. I’m afraid conventional matter it is.
> it's just some aliens that are not pointing an antenna straight at us
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?
Yup, information theory says that Gaussian signalling is optimal in term of bandwidth utilization in many cases. And we've spent decades trying to achieve this by various techniques in coding and modulation. And yes encryption/secrecy adds another layer of randomization. I believe a radio signal eavesdropped from a US military base is not much different than some random noise.
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.
>The paradox is that the our solar system should have been visited. But so we haven't been able to detect anything.
>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).
Flip the point of view for a moment - what's the absolute best way we could try to say "hey, we're here" to the universe in the hope of detection from far away civilizations?
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 :(
>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 :(
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.
Hmm maybe. If anything, I don’t think it would be killing for competition. Killing a planet is “easy” if you can expend the energy. The risk of accidentally offending another civilization is much easier, offending them to the point of them wanting to wipe you out isn’t that much harder (see Earth History). Thus, it almost makes sense to just wipe out any civilization preemptively.
Yep, I think it makes little sense for them to fear competition (if they exist). I suspect that intergalactic warfare is impractical and there is nothing to gain.
Reasons being: There is no stealth in space, there is no FTL, resources are abundant everywhere, destroying planets/megastructures is rather easy.
If an advanced civilisation was so advanced that it could hop around the galaxy on a whim, why would they come here to destroy us? It's not like the would possibly need any of our resources
It's not difficult to think of realistic (if not necessarily sensible) motivations if we try.
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.
We might be able to see their drive plumes if they use some of the theoretical high performance reactive drives we know of on big crafy. Eq. various fusion plasma drives, Orion, Nuclear Salt Water Rocket release so ludicrous ammounts of energy that they might be visible over interstellar distances, especially if pointed in our general direction when running.
Massive solar sails as well would be very very big and very reflective.
> release so ludicrous ammounts of energy that they might be visible over interstellar distances
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.
I'm not convinced we would be able to view any of those. The only exoplanets we've been able to directly image are huge gas giants that emit a ton of infrared light. A massive solar sail will likely be much smaller and emit a lot less light.
And most exoplanets are observed indirectly: doppler effects on the central star's light, occlusions of the central star's light measured through variances in the observed light from that star, and in a few cases absorption spectra of the exoplanet's atmosphere, again, by occlusion of the central star.
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.
Space is large. If you don't look in some direction, you don't see what's there. Big, or not.
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 ?
Here's an amusing thing. Even if they were within Jupiter's orbit and decelerating and pointing straight at us, we wouldn't be able to detect them.
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.
Rocket propulsion benefits from directional discharge.
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":
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.
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.
Nowadays there are satellites with omnidirectional gamma-ray detectors to detect gamma-ray bursts, so that optical and other telescopes can be turned on them.
Its a question of if these would be sensitive enough, but I think we can only expect the detection satellites to improve over time.
There are other methods of detection and signatures that, assuming similar civilizations to our own also follow similar energy use growth patterns, should be detectable at very far distances in other ranges of wavelength.
The universe we find ourselves in isn't very compatible with a species like our surviving for an extended period. If humans exist for millions of years we're going to either spread out to fill the galaxy or our machines will. The fact earth was free to develop us means that no other species like us existed long enough to beat us to it.
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 argument seems to violate the basic rules of exponentials. If an advanced species did settle on an stasis, then that will only last until some subset of the population decides to go beyond the stasis. Particularly for a space-faring civilization, the time scales and resources are so fast, that any multiplication factor beyond unity will eventually go bananas. Any individuals with the prerogative to multiply will swamp those who lack it, same with Earth evolution. The selfish gene will prevail unless there is centralized control.
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.
I think the answer is pretty obvious, we are the precursor species.
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.
Us being (one of) the first species is the most likely answer IMO. It violates the anthropic principle, but that doesn't account for everything.
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.
we are extremely close to the beginning of all existence
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.
The anthropic principle would hold that we as a species and our circumstances of existence are entirely average and not at all special.
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.
Von Neumann pointed out that an advanced civilization, with technology that we can predict should be developable, can colonize the entire galaxy in roughly 10 million years.
Von Neumann was much smarter than I but for such a calculation you have to make so many assumptions as to make it worthless. How can we possibly be able to predict what happens to a civilization in 10 million years?
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.
That doesn't really solve the problem because the simulation is (apparently) big enough to allow life to evolve. Why couldn't life evolve multiple times in a simulation?
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.
But in real life, it never actually is an exponential. There always is some limiting resource or saturation point or something, that turns it from an exponential into an S curve. An argument based on "the basic rules of exponentials" typically ignores second-order effects (there seem to always be some, even if we may not be able to see them in advance).
> 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.
Well yes, after the distance to the our solar system’s other resources, the next pauses in exponential expansion would be crossing to the next star system, then the spaces to other galaxies, and then to other galaxy clusters.
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
There's no exogenous law that exponential trends continue indefinitely. In fact I'd argue it's much more common to see sigmoid behavior where eventually negative feedback loops cause a plateau.
Yes, this is true but only from the reference frame of the cosmic background radiation. It is still possible that you can get O(n^3) from the reference frame of the aliens themselves, because time dilation makes travel fairly fast. You get into some spacetime philosophy about what metrics are worth evaluating O against in the first place.
> 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.
Yes I wonder if there was some particular condition that prevented higher intelligence to occur before recently. Or if it's just sort of "pure chance".
We are actually running out of places in our history to fit a great filter. Most of the events in our evolution seem probable, even inevitable. In fact the only place IMO that's really left is the emergence of the first self replicating RNA molecule. But even that seems too probable to be a great filter.
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.
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.
Good comment. I would add that our Sun is alone, while up to 85% of solar systems are at least binary. It's possible multi-star systems make life more difficult. Similarly, Earth's magnetosphere may be uncommon, since we don't see a similar one on Mars or Venus. And maybe Earth's rotation is uncommon and many planets are tidally locked.
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?
We don't know how rare either actually is. For both we have just one example - us. This suggests odds of no more than one in several thousand. But it doesn't take too many filters of that order of magnitude for a few hundred billion to become a handful, and the handful to become just one.
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.
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.
But it comes back to the number of chances. To wit, there's approximately 200,000,000,000,000,000,000,000 stars in the universe. We might be that one in a 200,000,000,000,000,000,000,000 shot where it all came together to create life but it's rather improbable. Almost certainly is other life out there.
That's just counting the visible universe. We have no idea how much farther it extends!
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.
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.
> We are actually running out of places in our history to fit a great filter.
Other than the obvious, which is the utter physical, technological, economic, political, biological, and statistical impracticality of interstellar colonization.
Techno-optimism. We didn't have planes, now we have planes. We rode horses and now we go to the moon. Therefore, anything you can possibly imagine is inevitable because "technology".
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.
I am not convinced that self replicating machines spreading out between stars is possible. There's rather a lot that the machine has to be able to do on a destination planet to set up mines and factories etc before the first extra machine can be made,and it has to survive landing.
This paper seems to explore a question I've had for a while which is: What is the maximum distance an Alien civilisation could eventually detect life signatures from Earth assuming their detection technology matches ours? I know that our current radio signals extend 100 light years or so but at which distance could these eventually be detected?
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.
Our electromagnetic shell drops below the noise floor around 15 light years out for say 5 MW military radars. For coherent signal decoding into carrier wave and payload waveforms as opposed to being able to point to a signal and say, yep that's not natural, probably around 5 light years out. Some discussion here [1] to get you started.
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.
I would guess advanced civs don't bother with radio and look instead for direct visual and spectrographic evidence.
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.
For baryonic-matter-based technological civilizations, above a certain technology level there is precious little to no such artifact as "waste", especially waste with energetic properties of any kind. Baryonic matter is vanishingly rare in the universe compared to the size of the universe and dark matter, so I wonder if someone there is dumping radioactive isotopes whether that is another SETI plateau like we hold out conjectures for about radio signals today transitioning to low-power digital signals, and one day we'll notice the spectral output changing.
With correct encoding you can detect signals way below the noise floor. Thats how GPS work, you detect a satellite signal orbiting at 400 km with an antenna the size of a chip.
The Curiosity rover communicates with Earth from Mars with an antenna the size of a soda can.
But the receiver has to know the encoding to be able to detect it. Maybe the aliens are using a different type of spectrum spreading technique that makes a lot of sense to them but is unknown to us.
May be true for radio signals, with the possible exception of OTH radar? But there are other technosignatures such as atmospheric composition that they may also be able to detect at substantial distances I think.
Perhaps I'm missing something, but this seems to get the Fermi Paradox backwards. It explains why we haven't been visited by aliens (the light-cone of our radio transmissions is small and therefore aliens outside of it couldn't send probes to us), but the key observation of the Fermi Paradox is in the other direction; why can't _we_ see _other_ civilizations, in all of the billions of years of history in our light-cone?
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).
> [The Fermi Paradox] explains why we haven't been visited by aliens (the light-cone of our radio transmissions is small
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.
Yeah, this is where I've landed on Fermi. It's very likely life exists elsewhere - possibly even on moons in our solar system. And it's somewhat likely intelligent life exists in other solar systems. But physics is such that it is much less likely two intelligences will be able to talk to eachother much less reach eachother. To quote Douglas Adams: Space is really big. You just won't believe how vastly hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space."
It routinely bothers me a bit that, IME, most IRL discussions of the Fermi paradox tend to omit this rather simple explanation.
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.
It routinely bothers me a bit that, IME, most IRL discussions of the Fermi Paradox settle on this rather simple explanation when the whole idea was that this "simple explanation" was extremely unlikely, pushing speculation to more complicated and interesting hypotheses.
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.
I doubt a civilization could survive being multi-starred.
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.
> A pissed off colony in the asteroid belt can sling asteroids at the home planet
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
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.
I really like this thread. Both make good points. I still land on space being really big and really hard. Maybe so much so that multi-stellar civilization is next to impossible and multi-galactic moreso.
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.
Even with FTL you have to know where to go. Let's say you do 100 solar systems per year (going somewhere close to the star and some local jumps to look around.) There are 100 billion stars in the Milky Way. It takes a billion years to sequentially scan the galaxy. Optimizations in the search algorithm to cut that number down to 100 years are left as an exercise ;-)
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.)
well, for some values of “very likely”. ;) I base it on extremophiles. Life exists in volcanic vents and freezing waters. So it seems possible that at least microbial life exists somewhere else in the universe. Either way, “is/has there been at least microbial life on Venus, Mars, or Jovian moons” seems like a solvable question in the next 100 years or so. The conditions for intelligent life seem much more narrow.
In my opinion, the excitement occasioned by the discovery of so many exoplanets has clouded our collective judgement on the Fermi Paradox, leading the overwhelmingly most probable resolution to be underemphasized.
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.
I think the probability of there being other life is much closer to 100%. There just has to be. Our universe offers way to much of the correct “stuff” that can create life that it just has to exist elsewhere.
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 life's probably fairly common. Like, bacteria-type stuff, maybe something like moss.
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.
If you grant moss and bacteria, then more complex life forms become inevitable. There are _advantages_ to be being multicellular, or multicellular life wouldn't exist. It's energetically advantageous for a plant to acquire a woody stem and stand up above the moss, or for a simple organism to work out how to have eyes, or teeth, or legs, or an exo- or endoskeleton. Assuming an environment that affords nutrients and is stable over a long time, once life kicks off it should keep complicating itself. It wouldn't stop at simple forms.
I fear that "much close to 100%. There just has to be" (as much as I too would like to share in this sentiment) may be an anthropomorphic projection and wishful thinking. Anthropomorphic because we are living creatures and assume that there must be other living creatures in the region of the universe we can see, even if just biochemically.
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.
I do not think so. We know nothing. We really cannot answer if there is life out there or not at our stage. Not until we figure out the loads of problems hampering our very ability to *start to answer the question in earnest. Not to say our efforts thus far do not count as they do.
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.
True that we know little and actually this is my point. I fear that "of course there is life out there in the universe" (as much as I too would like to share in this sentiment) may be an anthropomorphic projection and wishful thinking.
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.
I don't think people realize how quickly EM radiation falls off with distance, and how large the scale of "transmitters" would need be before we could detect.
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.
I also suspect that in time we will discover new mediums of communication that have better properties than the electromagnetic spectrum. Maybe when we listen on those mediums there will be a ton of chatter…
Within EM, gamma rays (highest frequencies) may be able to achieve sufficient spatial directivity for interstellar communication, but we'd have to be very lucky to have a beam pointed at us. Also currently our gamma ray receivers suck, and they have to be in space because our atmosphere largely blocks it.
On the other hand all those tech developments you pointed out we’ve only discovered and utilized in the last 100 years. Now imagine a civilization with 10 times that experience/time
Then you need to explain how life on Earth started a short period after it cooled down. Yes, it took a long time for complex life forms to emerge but life itself started right off the bat.
This may just mean that IF life is to originate, it will do so shortly after a solar system forms, or not at all. To infer that the early OoL means OoL is easy has the implicit assumption that the probability of OoL would remain about constant over time.
Easy to look up! By current estimates Earth cooled enough to have liquid water about 4.46B years ago and the first RNA emerged around 4.35B years ago. So it took just over 100 million years for simple forms of life to emerge.
Ok, so you are setting the scale as "from the present conversation back to formation of Earth" and saying that this is large in comparison to "from formation of Earth to formation of RNA". However, I respectfully don't see how this scale has any bearing on the probability of life forming around another system. Formation of life is certainly a prerequisite to the formation of intelligent life (the two events in question). Both could have a probability of occurring much smaller than 10^-24 (approximate # of finite stars in observable universe).
There is a pitfall with this line of argument in that it is appeal to intuition in a domain in which we have none, because we have no ability to intuit about large numbers.
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.
For a long time we weren't at all sure whether the expansion of the universe would stop, leading to a "big crunch", or continue forever, slowing down for eternity. Then we found the other option appeared to be supported by observational evidence: the expansion is accelarating.
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.
Yes, we know little (aside from the finiteness of the observable universe, which is known at a quantitative level). I am curious why then you say "so far, we're pretty sure there is some life in the universe, but nothing else." I fear this may be anthropomorphic projection and wishful thinking.
In a hypothetical total universe timeline of something like 100 trillion years, say till the degenerate era...we're not really very far in right.
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
If you look at the wikipedia's list of 100 nearest stars, only 4 are single main sequence stars: Tau ceti, Sigma Draconis, 82 G. Eridani, Delta Pavonis. All other are either binary stars with unpredictable orbits or flare stars. Stars where civilizations can quietly mature are rare.
Or they're not communicating using EM. And maybe they can't get off planet. And maybe the mean distance between pairs of civilizations is so large that interstellar travel is just not practical at all for any of them and us as well.
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?
All that's required to explain the Fermi Paradox is that it happen < 1 in an observable volume of the universe. The volume of the universe in which OoL could happen could be vastly larger, but we could never see most of it. Each extremely rare occurrence of intelligent life would never be able to contact any other, as they'd never be causally connected by signals traveling at the speed of light.
How is this the biggest mistake? So far it does appear to be the case. What negative consequences have come of believing ourselves to be unique? We have yet to find, on our planet or elsewhere, any creatures that build complex systems out of dead things.
He's engaging in a kind of ad hominem argument, that believing we are unique is a morally questionable position, therefore we must believe otherwise.
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.
How would your perception change if life was discovered on the moons around Saturn and Jupiter? Does that increase the likelihood of life outside our system?
If it was biologically similar to Earth life, it wouldn't prove much of anything, as it could have gotten there by impact panspermia.
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.
Here is a plausible alternative scenario. As planets form, there is a certain window of opportunity where conditions are right for life to get going (among other extraordinarily unlikely accidents that must come together, the phase of planetary evolution must be just right). Almost always, this too fails. After all, every attempt to date to recreate primordial conditions in the laboratory have failed to produce any life.
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.
I think the first alien we ever encounter will be something like a bacterium or virus, it will spur a debate as to whether it's really life, and it might already have happened.
If something visits us from another star system it's also likely to be an AI.
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.
If we're talking about galactic distances and timescales I don't see why we couldn't safely assume enough technological advancement for either aliens or humans to modify their own biology to the point where centuries would be a small fraction of your total lifespan. I think the bigger question is why any significant number of people would travel to more than a few star systems if you had to do it slowly. If the system is uninhabited then you would be isolating yourself from the rest of society for a long time. If it's inhabited then you would have the excitement of discovery and contact but it would still be difficult being separated from your own civilization and you would want to return at some point even if just to share what you've learnt.
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.
If the Internet has told us anything, it's that as soon as the production of a self-replicating probe becomes accessible to a hobbyist, some people will do it even if there's no benefit to them. And it only takes one. The far future human colonists won't be landing on unspoilt wilderness; they'll be reclaiming systems from some 25th century script kiddy.
What's hard to comprehend is how there could be a possible way to preserve our consciousness through a hibernation state. Like, our cells might not die, and we might be technically revived, but we'd still be brain-dead.
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.
I often find myself wondering if the same is true from simply going to sleep at night.
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?
Do you ask yourself the same questions before undergoing anesthesia, or even going to sleep each night? The experience would be identical (unless you believe in some kind of life after death) - since consciousness just stops, and you can only hope it will pick back up later on. Whether it actually will or not doesn't affect the experience you have right now though.
What if consciousness is something that can only be revived, with the revival of the body, a short period of time after the body "shuts down"? Like its own non-physical life form, for lack of better description.
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.
I don't find it interesting at all. Other than wishful thinking I don't see any reason to suppose that consciousness is special or non-physical. I think it will become like the assumptions that the Earth was the center of the Universe or humans were different from other animals.
Even for an AI, you'd need storage media that are stable for thousands of years, and hardware that will still turn on after thousands of years, and solar panels that are still functional after thousands of years. Oh, yeah, and a fair amount of those thousands of years will be exposed to radiation, including relativistic iron nuclei (fun stuff).
We might not know enough about what intelligence is to recognize it in any other form than the human form we’re familiar with. It could be that we start recognizing several other forms of intelligence around the same time, not necessarily because of new observations becoming available to us, but because we learn more about what intelligence looks like.
The Fermi paradox assumes that "intelligent" is one threshold, and we are beyond it.
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.
So a fun thing to try to think about is "What's missing from our intelligence?"
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?
IMO It is not only the possible form of intelligence at the personal level that counts, but also the aggregate "intelligence" of all humans. This is more easily imagined. To put this crudely, have you ever thought (maybe after an encounter with some person), how better our society would be without all the "backward" (no offences) elements?
An ET civilization will certainly judge us at that "aggregate level" (However that comes about)
If you look at animals on earth, they just aren't curious about many of the things we are curious about. My cats for example don't find television interesting.
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?
Your cats don’t find the tv interesting because they can’t even see it. Their visual refresh rate is different enough from humans that they just see flashes of images (a refresh rate above 100hz is needed for cats to watch tv or see a screen, IIRC).
I don't think making Youtube videos go at 4x speed will result in more interest from the cats, but I'll test it later.
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).
The speed of the YouTube video doesn’t matter, it’s the refresh rate of the tv or monitor that matter. With a tube tv or older lcd screen, it just looks like a flashing gizmo.
I have a 120 hz Oled Android TV. Unless Youtube drops frames speeding up a 30 FPS video 4x should hit 120 FPS.
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).
I’m not talking about FPS. At all. It doesn’t matter how many FPS there are. I’m talking about the refresh rate, ie, how many times per a second the hardware updates the screen which is in no way related to FPS, which is how many times per second your video card fills the display buffer.
I don't follow. All high end OLED TVs these days have a 120 hz refresh rate. This would appear to disprove the idea that TVs have too low a refresh rate for cats.
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.
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.
We as a species are very hostile towards all forms of life on earth. Some of us are scientists and open to communication and peaceful existence. Some of us are locusts, everything is devoured for personal gain. Our track record for meeting other species and other human cultures is such that were the roles reversed, meeting a human traveller from another star system would better be met with armed resistance.
The author raises an interesting question in his notes - human nations & races have for much of human history distrusted each other & gone to war. And yet we broadcast our location and welcome out into the cosmos assuming that alien species will be benign and friendly!
IMO that fact is actually a pretty strong reason to doubt the dark forest hypothesis as a serious explanation for the lack of observable aliens. If we've broadcast ourselves to each other for thousands of years and now even to the universe, why should we expect that every single other civilization out there is consistently doing the exact opposite?
Arguably we've only been broadcasting outwards for something like 50 years, so the message hasn't gotten that far yet.
There was a plot element in the book about using a technique to broadcast a message more strongly than terrestrial antennas alone.
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.
I thoroughly enjoyed Cixin Liu's Three Body series. Even if wildly unlikely I find the idea kind of comforting to existential dread despite it being possibly the worst fate for humanity.
If there was an advanced civ that fears competition, waiting for a random radio signal and then venturing on a crusade would not be the smart strategy.
You could instead launch relativistic kill missiles (pieces of rock) at all the planets in the galaxy before other civs emerge.
honestly i find the chain of suspicion to be the most problematic axiom for Dark Forest Theory. for example the turn of events with Bronze Age and Quantum, and eventually Gravity to be very unlikely, if enjoyable storytelling.
Until SETI locates something like a pulsar braking and accelerating to signal prime numbers we're really really really unlikely to stumble onto more life. Space is just too big.
But is it? We can detect things about the chemical makeup of the atmospheres of extra solar planets. Our own atmosphere is broadcasting the likely presence of life, plus near certainty of industrial civilization. We could detect that up to some distance with our technology. What could advanced aliens detect? What if they used gravitational lensing to magnify the signal?
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.
Our signal for oxygen and other bio-signatures is so much stronger than the signals we have been sending recently and it's been going out for...quite some time.
I mean, the Great Oxygenation Event is ~2 billion years in the past, and the Cambrian Explosion is only half a billion years ago. If intelligent, space-faring aliens checked it out, there's a 75% chance they arrived while the most interesting thing on Earth was, well, I can't think of anything that wasn't "technically before the Cambrian but like, only by 50 million years". Fungi?
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.
Well, you're almost certain to hit a hydrogen atom within a meter of travel in deep space. Larger objects will be less common, no doubt.
> 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.
How far away do you think such a thing could be detected? Say someone set off a 100 megaton nuke in space within the Centauri star system. Could we detect it?
Well, someone running a nearby Dyson Swarm might as well run a couple thousand telescopes when they are at it, even to just make really sure no habitats are ending up in collisions with comments and extrasystem asteroids. In spare time such system could be used to look for interesting stuff in other systems, possibly like a big synthetic telescope of some sort.
its inverse square falloff for radio energy dissipation so I'd say it goes away really really quickly. also you have the problem of overcoming Sun's 'blaring' background signal unless you took your signal generator and placed it outside of oort cloud or further.
Another idea is to put a mylar parabolic mirror behind the bombs. A very short burst of light is going to get focused in a beam before the mylar is vapourised. Maybe someone smart here could calculate exactly how short the beam would be.
That short burst could be in itself a significant signature. What, in nature, could produce such a short concentrated energy burst?
problem with such a tight-beam is you have to be in direct line of sight for it to be seen. which means a very small number of receivers civilization can ever know, that is exact opposite of the goals of a 'lighthouse'. perhaps something that sweeps around at regular intervals with some precession thrown in for coverage, that makes it closer to GP's comment about neutron star emitting prime numbers.
oort cloud is just a stand-in for generating enough parallax in the signal from sun. further out you go better it would be. in fact it just occurred to me that you could just launch an emitter perpendicular to galactic plane with enough velocity that it bobbles up and down say 3x over what a normal star would and it would serve as a galactic lighthouse for intelligent civilization.
Luckily, the aliens are wearing Swiss wristwatches, they know how long a minute is, and so are able to notice that the intervals are a prime number of minutes :-)
OK, that makes a bit of sense. But I don't know what it means for two real quantities to be relatively prime. Primality is about factoring, right? And you can only factor integers. So to observe primality, you'd have to partition interval measurements into an integral number time-units.
Can two reals be relatively prime no matter how you partition them into integers?
You're looking at the sky and you see a bright and otherwise unexpected signal. Then you see it again, some time later. You write that time down as T_1. You don't know of any astronomical phenomena with period T_1, so you wonder whether this could be a weird rare event. Then you see it again, spaced by T_2 this time, and you start to wonder whether it could be a purposeful signal. Then T_3 etc. How could they be linked? They're getting farther and father apart, so maybe it is a sequence with some significance. Maybe it's the fibonacci sequence for example. So you try dividing all the intervals by T_1. And you get 1,1.503,2.496,3.500,5.506... huh, lots of nearly-half-integers in there, maybe T_1 was supposed to be 2 units actually?
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.
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.
If the precision between the intervals is good, how can you not get to primes?
Of course the intervals would be real, but there would be a very discernible pattern.
It would stare you in the face, or what am I missing?
I disagree. Sequences of reals are still sequences. So maybe hypothesis one has nothing to do with integers, maybe it's that the intervals are increasing geometrically. You're still going to take ratios and and start having suggestive numbers fall out. "can't just switch ... without explanation". The point is that this putative alien observer would be looking for the explanation. Maybe the first few explanations they come up with are the wrong ones, but they are trivial to check. It's not like it's a research project to reject the Fibonacci hypothesis.So you would still have the right answer on day one.
My pet theory to address the Fermi Paradox is that we live in a unpleasant place in the universe/multiverse. Out there, exists a place much more attractive (think of another dimension with much better physical properties). And this is where everybody is.
Before we worry about communicating with civilization far away in space but coexisting with us in time, we should work at communicating with civilizations coexisting with us in space but far away in time.
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!"
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.
If you like thinking about the Fermi Paradox, a series that might be enjoyable is the Universe Today's Beyond Fermi's Paradox [0] , it is about 17 articles on different aspects of the problem along with links to papers and essays to make it easy to go deep into a topic.
Good grief, did anyone read the paper, or are you all just sprouting your own personal Fermi paradox theories?
> 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.
Well, I didn't notice the bit about a "noisy period" - I took the sphere to be the surface of a volume, not a shell. I think the idea was that once you start emitting detectable information, you don't stop.
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.
Even a very efficient and radio quiet civilization would still have to release obscene amounts of heat if they do any serious stuff in space. Unless they somehow hack thermodynamics there is really no way around that.
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.
I feel the same way. How do the SETI people explain this away and justify their search? One light year is tiny, I think it would take an incredibly generous Drake equation estimate to make that contain intelligent life. Same for 100 light years too. But I lean towards pessimistic Drake equation values. Life is even more rare and precious the more I dig into the equation.
> 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.
I would have to assume that they know this and are in fact only looking for messages that are purposefully sent at very high power. It's also why they favor listening at the hydrogen line since transmissions at that frequency stand the best chance of penetrating through cosmic dust, i.e. you would only use that frequency if you were intentionally trying to transmit across interstellar distances.
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.
For me it boils down to- would an advanced civilization beam out a very strong locating signal on purpose? They would have to be very certain they were the baddest strongest civilization in the galaxy. I can’t think of a way intelligence and that idea go together.
With one single data point, we presume that life is ubiquitous in the universe and that intelligent civilizations probably exist in more than one place, yet we assume that everyone else is scared to give away their position, even though we aren't. If we can presume intelligent life is out there even though up to now we only know of ourselves, why not presume that that life behaves like us in at least this one way? Seems paradoxical to assume differently, no?
I don’t think we are that intelligent obviously. When I watch the news this is confirmed. And when we send out a “look here and come plunder” beacon it is confirmed as well. We just exited the campfire stage a hundred years ago or so. An alien civilization could be millions or billions of years ahead of us with weapons that we can’t even imagine.
There are other techno-signatures to look for: Dyson swarms (marked by irregular dimming). Infinitely more powerful transmitters - i.e. irregular pulsars. Oumuamua type fly-bys. "Unnatural" gasses in atmospheres.
All purely theoretical, of course. As far as we know, we might not even notice life on Alpha Centauri planets 4ly away.
I think a big Orion drive powered spaceship flight profile would be widely noticeable. Like, nature rarely produces hundreds of sequential nuclear detonations in deep space in quick succession, possibly perfectly matching high energy transfer orbits.
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
> Non-directional radio transmissions (e.g. TV, radio) would not be distinguishable from cosmic background radiation at more than a light year or two away
this is going to come across as sarcastic in text, I genuinely mean this.
Because I suspect that under focused analysis the signal won’t quite look like cosmic radiation background.
Now I also haven’t done the analysis, but information, and entropy are funny things. Will they get to watch a human TV show ? Hell no. Would it look “random” versus showing that it once contained some structured information ? I think that’s a very open question.
There are probably more serious papers that deal with the matter and how long and far “techno-signatures” survive in the noise.
An old NTSC video signal has a clear periodic structure. Simply counting lines is going to reveal a lot about the structure and if anyone gets the idea of plotting lines they will figure out how to decode it.
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.
Makes me wonder if alien life will actually not find our messages simply because we're using such "ancient" techniques. Perhaps they invented a TV like object and used a NTSC like signal, but like 100k years ago and no one in their race knows to look for our old signals. Maybe our comms look like hieroglyphics to them ?
Periodicity is a clear signal that is useful for natural objects like pulsars. I think it would be very clear that analog videos are periodic at the line level and periodic at the frame level. If somebody gets the idea of plotting signals on a grid they will get a sequence of frames. Even creature that don’t see the way we do might develop some kind of raster basted signal processing.
On top of that TV signals would have additional periodicity because the transmitters will be hidden behind the Earth once every 24 hours.
I've been wondering what the advantage of von Neumann probes are. Once you have the ability to autonomously construct probes, it seems like it would be easier and faster to mass produce them in one solar system and send them directly to their destinations.
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.
To send you back any information, your probe has to either send back something physical or use the electromagnetic spectrum. If you send a probe with no manufacturing capacity, then it either has to carry all the fuel, shielding, and redundancy for both directions of the trip, or carry a very large radio and its much larger power source. That's gonna be really, really heavy. Probably heavier than the manufacturing machinery. So you would want to be able to manufacture just so you could report back.
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.
Like you said, if you want it to do "something interesting," like building a colony, we're not talking about probes anymore. But even then, it seems like mass producing the would be faster.
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.
If the probes don't have replication devices in them, what are they doing?
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.
If you've achieved enlightenment and freedom from all desire, then it's a bit weird that you're posting on Internet forums. If not, presumably you'd quite like to not be turned into a paperclip.
Hey, if they can't build a swarm that does something more fun than that, why would I think I could? I mean, my own swarm is subject to value drift and may also clip me.
The point is that solar systems have tiny amounts of resources when compared against the idea of colonizing an entire galaxy, whereas the concept of a von Neumann probe swarm would have resources proportional to the task.
Now, whether that is actually possible in any serious sense is very much in doubt.
There are ~2 x 10^9 stars in the solar system. The mass of earth is 6 x 10^24 kilos, with about 1/3 of that being iron. So even if we're just using the mass of a single celestial object the size of the earth, and only looking at iron alone, that'd be 1,000,000,000,000,000 kilos of iron you could use per star (for reference, this would be the equivalent of ~300 million fully fueled Saturn V's per star). It seems like a single solar system would have enough resources.
I am quite certain that using all of the iron in a single planet's core is well beyond the difficulty of building a self-replicating probe (which itself is well beyond our technical capabilities).
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.
If you want to restrict yourself to the earth's crust, that'd still be ~5,000,000,000,000 kilos of iron you could use per star, or 1,500,000 Saturn V's. And that's just using one planet.
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.).
The fact that you're talking about Saturn Vs and landing on planets and taking off again shows that you're considering the wrong paradigm entirely. If you're landing on planets you're already doing it wrong. Atmosphere and gravity wells are the enemy. Remember, even the non-self-replicating probe still needs to be self-repairing, since in your scenario it has to last for probably a million years' worth of radiation and micrometeorite damage. A million years' worth of spare parts is probably a much bigger investment than some automated manufacturing.
I brought up Saturn V's to give people a sense of the mass we're talking about, not because I thought the probes would be actual Saturn V's (and I don't think we'll be sending 1.5 million of them to a single star).
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.
The problem wasn't that you thought they would be actual Saturn Vs, the problem is that you think the mass of a Saturn V is remotely enough to send a probe to the other side of the galaxy. Designs for intra-galactic probes typically include meters of shielding because of how nasty hitting even a grain of sand is at interstellar velocities, and in your case this is even worse, since said shielding doesn't have to stand up to a century of ablation, it has to hold up for a million years. You're exceeding the mass of a Saturn V on shielding alone, and the tyranny of the rocket equation still applies. Building bigger means building everything else bigger.
Further because a sufficiently powerful compression+encryption scheme would be indistinguishable from noise, how would we even know any pattern is or isn’t a natural noise or an artificial noise?
My pet theory (which I'm sure is not original) is that absolutely all intelligent life, through AGI and/or genetic engineering, eventually converges into an undifferentiated super intelligent state.
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.
Yup, feel like there's a "strong attractor" to a non-biological super intelligent end-game for any civilization and this happens relatively quickly once their species enters an external-to-biology recursive self-improvement state (e.g. humans discovering, externalizing, and transmitting technology over multiple generations leads to recursive self improvement of technology).
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.
Yes, my extremely layman pet theory is that dark matter / energy are the evidence of advanced intelligent civilisations too; just we don't understand what we're looking at yet.
My problem with this kind of things are its assumptions: life is made of carbon, every discovery being conditional probability of being discovered, each civilisation makes exactly the same chain. And the biggest of all: life is the most general and important thing for everything that comes to be in the universe. I.e, everything lives in our own terms
If I were an advanced civilization with some sort of jump technology, I'd have probes jump to different solar systems for only a few milliseconds, which would be more than enough time to collect technosignatures. I wouldn't wait to for the technosignatures to come to me.
It always amazes me that right now, as I type this comment, there could be countless intelligent civilizations out there with their own histories, philosophies, science, literature, etc. All asking themselves the same thing: "are we alone?".
If you assume that intelligent life has to pass a certain number of "steps" to develop, doesn't the central limit theorem dictate that the more of those steps there are, the closer in time each separate species will achieve intelligence?
Incidentally, my statement above is incorrect on a couple of levels: first, I was thinking of the law of large numbers not the central limit theorem, and second, even the LLN would only say that about the average step length, not the total time to the end of any step.
The central limit to theorem states no such thing even if the steps vary independently.
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.
SD is defined by dividing by the square root of the number of samples. It is never divided by the mean - as this metric has no relevance.
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.
The variation in the random variable relative to the value of the random variable is fixed. It doesn't change, no matter how many times you sample the random variable. It's called the per-sample standard deviation.
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.
i feel like its premature to discard the possibility of FTL travel and it should be taken into account when discussing the fermi paradox. if FTL travel / FTL communications exist, we have no means of detecting that
Focusing on radio communications for SETI purposes and as a solution to the Fermi Paradox I find to be incredibly outdated thinking. Let me summarize:
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.
You're ignoring the temporal aspect. A dyson swarm would be visible thousands of light years away, thousands of years after it happened. Humans current technological kick start has only been going on for a hundred or so years. Our entire known history, complete with dark ages, is a few thousand years. By the time something even sees it, who knows how much such a civilization will have changed. Would the dyson swarm even be there? Would the civilization? Is it even worth investigating?
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, 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.
I'd suspect the vast majority would. Apex predators are pretty much the only niche that gains any incremental, real utility from investing energy in increased intelligence. What benefit would an individual slightly smarter manatee acquire?
Scavengers are probably the second most likely to develop intelligence, and I was definitely thinking in terms of carnivore vs. herbivore. Intelligent scavengers such as corvids and raccoons come to mind. That said, it's quite possible to scavenge with limited intellect. Vultures, for example, are somewhat intelligent, but not the extent of a dolphin, wolf, or primate. Additionally, a sufficiently intelligent scavenger will probably eventually turn to hunting. If you've got tool use, and are hungry for something dead, it's not a terrible leap to kill the thing yourself.
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're in the process of wrecking our own ecosystem.
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.
Above statements are proving my point. Despite its many flaws human civilization is stronger than ever and is on the verge of expanding beyond the home planet.
Proving what? With a sample size of 1 that is all just survivor bias so far... and after all we know it is ending soon
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..
Really? You don't see how our civilization is stronger than it's ever been? You don't see how we are on the verge of expanding beyond our home planet? Just, don't see it huh? Perhaps you're not the person that should be explaining to everyone what is painfully obvious and what is not then.
> Perhaps you're not the person that should be explaining to everyone what is painfully obvious and what is not then.
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.
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.
If we assume alien life in the universe is predatory and seeks to consume other life forms, and since the universe allows detection from other species over infinite distances and time scales, we would expect life in the universe to either be totally undetectable or else be consumed by life that is totally undetectable.
That's not a great starting assumption. How would the economics of travelling hundreds or thousands of light years in order to "consume" (whatever that means) other life forms work out? What is the benefit? How would it be worth the investment?
If you are talking about a dark forest then it is more opf the idea that any other sufficiently advanced civilization would simply destroy you as soon as you are known to them rather than attempting to consume any potential resources you have as that isn't economical. The most economical thing could be as simple as sending a small object at light speed through your sun to cause a supernova.
This eliminates you as a potential threat and you have no chance to use other limited resources outside of that system.
While your main point stands, I doubt that crashing even a moderately sized planetoid into a star at any achievable speed would do much to that star. It definitely wouldn't cause a normal supernova.
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.
At least as far as our current understanding of physics it is probably not possible to accelerate an object to the actual speed of light, but who knows if there is some kind of universe hack that we don't know of.
maybe not a planet but a mini blackhole tugged by a small ship at high velocity to crash into your sun and turn it into a proper black-hole with accretion disc and the works would do some serious damage to you as a species.
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.
Bold and odd. I read Under the Skin. Excellent and innovative sci fi, but nobody goes that far and spends that much even for a Kobe beef burger. Even here on bloody barbaric Earth, weapons exist mainly to keep trade from being disrupted and the largest military has an environmental compliance department.
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?