So what if you do find someone. Are you gonna meet them? Send them a text?
Astronomers have been offered a cheat sheet on the kinds of things to look out for – from air pollution to energy production – when hunting for signs of intelligent life on faraway exoplanets. “We have no idea whether intelligence is something very common in the Universe or, on the contrary, whether it is extremely rare,” said …
What would it do us of good to build and send such a missile if the other side has already launched one (or will so so before our missile arrives)? At best, satisfaction when we all die that we will be revenged, but that is a poor comfort.
And, in the event that such a missile misses its mark or is intercepted, we will have made an enemy that might otherwise have been an ally.
Interstellar distances are so large that invasion of another civilized planet is unrealistic. We can destroy one, yes, but invasion assumes that there is something worthwhile left to invade. And the amount of war material that it is realistic to bring across interstellar distances will be relatively easily countered by the defender, even if their level of technology is lower -- as long as they have orbital capability. Added to that, invasion is only really worthwhile if the goal is colonization -- sending goods back to the mother planet is too expensive to be worth it -- and sending a large number of colonizers across interstellar space is unrealistic. This is why invasion SciFi postulate hypothetical technologies such as FTL flight.
It might make sense to colonize extrasolar planets that have biospheres but no civilization. You can send frozen fertilised eggs there and let them be raised by robots until they grow up. This will in no way help Earth, but it can ensure long-term survival of the human species.
> What would it do us of good to build and send such a missile [?]
Hiya Torben! The game theories that SecretSon is referring to aren't related to colonisation, invasion or any motive of that type.
Instead they are a chain of reasoning that a civilization might follow out of self preservation.
(Indeed, the very large distances and timescales involved are a reason why one civilisation can't ignore another civilization as 'mostly harmless' since technological advancement might be exponential - in the few centuries it might take to meet them their capabilities will be hugely expanded. )
Just to be clear - I'm not advocating for firing a missile* at the first extra-Solar civilization we encounter (and if people here thought I was, then I'm glad they downvote me!)
I am, however, just noting that the game theories in question (which are just some of many theories advanced to explain the Fermi paradox) involve hiding from all other civilizations and destroying all other civilizations at every opportunity.
The reasons for doing so fall out of the game theory for reasons of imperfect information, trust and fear - they are not built upon motives of empire building or colonisation, or of securing resources.
Again, I'm not advocating for this (and indeed the first thing any thinking person sees in the stake equation is a load of factors for which we have no or little data), but it's just as worthy of consideration as any other explanation for the Fermi paradox.
* By missile, we mean single attack that kills all. Deathstar style. Lobbing rocks at tanks this isn't.
Downvoted for a lack of imagination/humility.
In the age of sail, it took days or weeks for invasion fleets to sail from their home port to their target.
Now we have nuclear-capable bombers that can reach any point of the globe in under 12 hours, firepower and accessibility that were unimaginable less than 200 years ago (outside the realms of fiction). Just because we don't now how to do it at the moment doesn't mean it is impossible, or that nobody else has found a way...
In Star Trek, the Enterprise can't reach other galaxies even at maximum warp speed, and warp speed is highly improbable.
It's worth considering that as distant systems are so far away, it takes even light a very long time to get here. Thus they might not even be there any more when our multi-generational ship arrives, inevitably at velocities much less than C. Quite part of course from the maintenance problems of keeping a multi-generational ship working - particularly the computers (BORK BORK).
In the age if sail, unfortunately, we didn't have very-well-tested theory which said that travel faster than c could be bargained, using technology we understand very well, into a time machine. So one of the following really needs to be true: special relativity is hugely false in regimes in which it is extremely well-tested, FTL travel is not possible, or causality fails. It would be astonishing if SR was false (and I don't mean false in the sense that its predictions are a tiny bit wrong, I mean false in the sense that its predictions are not even ball-park correct) in this way. So that leaves FTL travel and causality failure, or neither. Well, we don't observe time machines.
Don't get me wrong: I'd like FTL travel to be possible too.
Tricks like that don't really help with the time-machine problems unfortunately. They may help if they are traversible only in one direction, but such things kind of are not useful for most scifi. You generally need all sorts of weird constraints on global topology which seem physically unnatural if you don't want CV.
(It's kind of entertaining that someone downvoted the parent of this!)
The whole futility of war on the interstellar scale features in the rather excellent Bill, the Galactic Hero by Harry Harrison (better known for the Stainless Steel Rat books). Basically, what you just said.
> Latest game theories say that in that event we should start building a lightspeed projectile and fire it at them. Just in case they are doing the same.
Such game theories explored in The dark Forest by Liu Cixin- indeed, the very title of the novel is a metaphor for a view of the galaxy as a dark forest, full of silent, stealthy killers.
Superpredator interpretation of Fermi Paradox
Whilst Mr Cixin writes convincingly, it is of course based on lots of unknowns (indeed, he shows how the dangers he describes stem from civilisations' reaction these unknowns / unknowables), so I'm not sure what to think.
There'll be another one along shortly, but they might be moving a bit sharpish:
"an average of 6.9 interstellar objects around the size of ‘Oumuamua – at least 100 metres across – should pass within 1 astronomical unit (the Earth-sun distance) of the sun every year.
The researchers estimated this by calculating the expected velocities of interstellar visitors and working out how long they should remain in our solar system. They found that the large majority should travel up to 100 kilometres per second, indicating they originate from the main plane of the Milky Way.
But a small portion – 0.03 per cent, or three objects per century – could have velocities of more than 530 kilometres per second, meaning they originated from outside our galaxy’s disc, perhaps even from another galaxy."
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“ Latest game theories say that in that event we should start building a lightspeed projectile and fire it at them. Just in case they are doing the same.”
Surely the trick is to trick them into thinking you’re somewhere else and waiting a few hundred years and observing if somewhere else is annihilated (Per The Dark Forrest)?
The last on the list to look for should be Dyson Spheres and Ring worlds, any species sufficienty advance and powerful enough to produce such artifacts are unlikely tp be so inward looking.
While such things make interesting sci fi, the likelihood of any existing is ridiculously low.
Pollutants seem a better bet but the list needs serious thought, many pollutants on Earth can be produced by nature as well as man, though some volatile compounds can be produced by plants and other lifeforms so they may be of interest.
Dyson spheres are only easy to detect if they exist, I doubt very much they are high on the to do list for beings sufficiently advanced to be able to construct them.
If the development of a species is sufficiently outward looking to drive them to space in the first place, I think looking even further outward would ultimately be more efficient than the immense effort it would take to encapsulate a star.
I am not an astrophysicist but I am a reasonable engineer, Dyson sphere construction goes way beyond just the physics and energy required build it, the infrastructure would be truly stellar
Dyson spheres are only easy to detect if they exist
Weeeeelllllllllll.... yes and no. The fact that they have such a characteristic signature which is easy to detect also means that their absence is pretty easy to detect: if you scan the sky and don't find that IR signature with no corresponding visible light, they don't exist. And that negative result would have its own implications which I could prattle on about until you beg me to please shut the hell up.
And as it happens we're just starting to get into infrared astronomy and doing really big sky surveys with orbital IR telescopes like JWST and computers capable of processing huge volumes of data like full-sky surveys. Given that we already have the infrastructure in place for other stuff and it's like an extra 5 lines of code in the software (ok, yeah, I exaggerate, but the point is it's not much extra effort), I think it's probably worth spending the extra 0.1% effort of looking for them.
looking even further outward would ultimately be more efficient than the immense effort it would take to encapsulate a star.
Cool story bro. But what do you do when you've colonised every star in your galaxy and find that you still want more energy and habitable areas to populate? If you're thinking you'll go extragalactic then you should bear in mind that the nearest galaxy is going to be on the order of a million light years away, and you'll need a big fleet to transport a population there, and there's a whole lot of nothing inbetween galaxies. Suddenly building those dyson spheres to more efficiently utilise the matter and energy already at your disposal seems much more feasible. And once you're at that point, you'll realise that it would have been much more efficient to just build dyson spheres in the first place. And if you do even a modicum of fore-planning then you'll come to that conclusion while you're still some primitive civilisation that doesn't even have interstellar travel yet ;)
(that's not to imply that going extragalactic is impossible or unlikely. But you would continue to build up your home galaxy, too, and that means dyson spheres)
In fact, there's not really much more to it than the physics and energy of it. If you're thinking on the long scale then building dyson spheres is basically the only way to go unless you've got some infinite energy cheat code or something similar which breaks our understanding of physics. Sure, you expand outward too, but you build dyson spheres as you go. The only other reason you wouldn't build dyson spheres is if you skipped that step and went straight to black hole farming. But doing that would needlessly and dramatically limit your available energy during the Stelliferous Era.
You're trying to guess the motivations of minds which are alien and unknowable. The assumption that civilizations will tend towards dyson spheres is not built on making assumptions about motivations, it's build around the physical matter and energy limitaitons of the universe. "outward/inward-looking" is subjective and not useful at all, because it requires making assumptions about alien psychology, something we have zero data on. The dyson sphere idea is not based on psychology, it's hard physics and it's the logical conclusion you reach if you're looking to maximise your available energy.
Another thing that I'd like to point out is that when you talk about the immense challenge of building a dyson sphere I'm pretty sure you're thinking of a dyson shell. Possibly because you saw the (awesome) TNG episode "Relics", which uses the term incorrectly. A dyson shell might be an impossible to build. A dyson sphere, on the other hand, humanity has the tech to start building one tomorrow. You might be more used to the term "dyson swarm". That's what we're really talking about when we say "dyson sphere". Nobody really expects to find a shell.
the infrastructure would be truly stellar
Ooh nice one!
No, I don't think that's more likely. Why would you?
The former is something we know could be built, with technology we already understand, for a huge payoff (in energy collection). The latter is magical unicorn-piss-and-fairy-dust idle speculation. A pure Bayesian reasoner would find the former more probable (evidence pushes its probability past 0.5). A frequentist would find no direct evidence for either, but prior proxies favoring the former.
Maybe they just perfected fusion, for example. That's not that much of a stretch.
No, it's not that much of a stretch, at all: I'm sure we'll do this. Unfortunately fusion also fails to be magic.
The Sun (which is, after all, a fusion reactor which has run for a few billion years now) produces about 3.8E26W, which is equivalent to converting about 4.25E9kg/s of mass to energy. The primary process to do this is converting 4 1Hs to 1 4He, and if you do the maths (just comparing atomic masses is enough) you can see this process is about 0.7% efficient (ie the 4He is about 0.7% less massive than the 4 1Hs that made it). So it's turning about 6E11kg of hydrogen per second into a little less helium.
I don't know how efficient the kind of fusion reactors humans will be able to build are, but they will be ball-park the same (for comparison the mass-conversion efficiency of a fission weapon is about 0.1%).
So if some future civilisation wants to use power equivalent to a star they will need to process somewhat more than half a billion tonnes of hydrogen per second. The fusion reactors to do this will, I guess, rather conservatively have masses of trillions of tonnes.
And they will be big: very big. They will need to have radiators which are absolutely vast: if you dissipated that kind of power from the Earth its surface temperature would be tens of thousands of degrees. If you want to keep the temperature to, say, 500K then the waste heat radiators are going to be a sphere with a radius a little less than the orbital radius of Venus.
So these fusion reactors are going to look ... a lot like a Dyson sphere: they won't occlude the light from the star, but they will be absolutely vast structures which are very bright in the infrared.
Well, if you can build these things you could could instead just build a Dyson sphere and let the star do the whole fusion bit for you: this would almost certainly be both simpler and safer. Either way, you are going to have some truly enormous collection of structures which are very luminous in the infrared ... which is what people are suggesting we look for.
But, you say, we don't actually need all that power. Well, OK, so we just build part of a Dyson sphere, or some number of relatively small fusion reactors.
But, unless things change we will start needing this kind of energy in due course. Human energy production was 18TW in 2013, and has been growing at about 2%/year for a long time (actually 2% is rather conservative). Like Dyson, I can do exponentials. If we are to continue this trajectory then in about 1500 years our energy needs will be the entire output of the Sun.
I'm not arguing "magic". I'm arguing that a civilisation that's got 500 years progress on us is going to know things that we don't.
But these "maybe they have super advanced tech that breaks our physics" arguments do effectively sum up to magic.
I assume you don't think that we know everything.
We don't know everything. But there are certain things that we have observed that seem to put some limit on what is possible in the universe we seem to inhabit.
For example, according to everything we know, objects warmer than their surroundings emit infrared radiation. It doesn't matter how advanced your tech is, black body radiation will still be a thing. If your tech is so advanced that you can have a warm object which doesn't emit IR, then you're doing stuff that appears to contradict the laws of nature as we understand them.
"oh but that's just our understanding", you say, "and our understanding is incomplete, so maybe there's some way to do it that we just don't know".
But the problem with that idea is that our understanding is all linked together. The black body radiation stuff is linked to our understanding of thermodynamics and entropy and quantum mechanics, and probably to a bunch of other stuff that doesn't spring to my mind immediately.
And if that one piece of the puzzle is incorrect, then it would have a "ripple effect" on our understanding of physics. If there's a way to not be a black body or to reverse entropy that would mean that a huge portion of our most basic physics is incorrect. And not just "incorrect", but "totally not even in the right ballpark". And we've seen no evidence of that being the case. And we've got tons of experimental and observational data that backs up the understanding we have and which seems to indicate that we're in the right ballpark and not too far off the mark in most cases.
So if you want to conjecture about new physics and warm objects that don't emit black body radiation, you're going to need to work really hard, and come up with an explanation for how that could be a thing that doesn't totally break our entire understanding of the universe.
And it's like that in a bunch of places. Another example would be that if you want FTL travel, you're going to need a good theory as to how time machines won't violate causality. That or you're going to need to explain how causality isn't a real thing but really seems to be to us.
Either of these two examples, and a bunch more, would rock the world of physics to its core. And because they'd rock physics to their core, you're going to need some really good evidence to prove that these phenomena exist. And I'm afraid that saying "oh maybe magic" doesn't live up to the kind of rigour the physicists are going to want.
There is no point speculating scientifically about things for which there is no basis for conjecture. Once you do that, you're not doing science anymore, you're making stuff up. Sure, an advanced civilisation might be able to get free infinite energy. And they also might be able to manifest leprechauns that don't emit black body radiation out of thin air whenever they fart. But the onus is on the person making such a claim to prove that that is possible. You'll also want to make your claims falsifiable so that they can be tested.
See also: Russell's Teapot.
I'm sure an actual physicist would do a better job of explaining this than me :)
Just thinking about it a bit more, another analogy would be that if you were to find an instance of a warm body that's not emitting IR, it would be kind of like finding a case where 1 + 1 = 3.
Imagine a situation where you have one apple, and you add another one, and then suddenly from out of nowhere without anything else happening you now have three. An apple didn't appear out of thin air. Nobody teleported it in. It didn't even appear out of thin air magically, because it's not magic, just math that we don't know about. You had one apple and you added one apple to that and then you had three apples. Does it seem to you like that might be something that a more advanced civilisation might be able to do?
The construction of a Dyson sphere would certainly be an incredible feat of engineering, but so too would be the system protecting it from all those inconvenient comets, asteroids, Kuiper belt objects and extra-solar oumouamoua type objects that just happen to fall into the local star's gravity well.
OK, so you could use some of the energy from the star to try to protect the structure of the sphere from physical impacts of large bodies, but meteor showers, and the fireball meteorite that fell on England recently would tax even the best space defence system to detect. Then there would be the ripple effects on the structure of the larger planets' to consider (there are gravitation reasons why Saturn's rings have gaps in them; why is the asteroid belt a ring of rubble and not a proper planet?).
No offence to the great Freeman Dyson but I reckon that constructing a Dyson sphere is difficult but keeping one in working order for even a enough time to recoup the investment is several orders of magnitude more difficult.
There are various versions of 'Dyson sphere' :
I don't think that many would use up as much mass as you suggest. If one did require most of the non-stellar mass of the solar system then we would never be able to make it. In any case, Oumuamua type objects arriving from another solar system would still be a threat.
we would never be able to make it.
You people who use the word "never" like this need to read The Last Question by Isaac Asimov.
In any case, Oumuamua type objects arriving from another solar system would still be a threat.
They're a threat in the same way that a mosquito is a threat to a 747.
Yeah, I'm not seeing the threat. Say you have a swarm-style Dyson sphere around the sun. Even in a tight orbit, the surface area is [some quick calculations] really big. Even a whole bunch of asteroid-sized missiles will just take out a handful of your many, many satellites.
Even if a shell-style sphere were possible, and we had one, and 'Oumuamua-class object whacked into it, so what? I mean, if you happened to be nearby, it'd ruin your day, but the odds of that are really low. And it's not like the shell would crack like an egg or something -- anything suitable for constructing such an object would be pretty tough. And it's inflated by solar wind and light pressure, while being tensioned by gravity and internal stresses.
(I'm not a solar-system engineer, but I'll play one on the Internet.)
I think that (a) people are thinking about Dyson shells as you say, which require magic materials so let's not think about them, and (b) the risk of something hitting and damaging some tiny fraction of the objects making up a swarm might be a Kessler-style event as debris started taking out other objects. Pretty sure that could be handled.
About 7 per year, it seems, so quite a lot in the expected lifetime of a Dyson sphere. See this article from New Scientist:
"The researchers estimated this by calculating the expected velocities of interstellar visitors and working out how long they should remain in our solar system. They found that the large majority should travel up to 100 kilometres per second, indicating they originate from the main plane of the Milky Way.
But a small portion – 0.03 per cent, or three objects per century – could have velocities of more than 530 kilometres per second, meaning they originated from outside our galaxy’s disc, perhaps even from another galaxy.
Read more: https://www.newscientist.com/article/2271307-seven-alien-space-rocks-should-pass-through-our-solar-system-each-year/#ixzz6pJBRTHlb"
OK, let's assume they're actually a threat. I still say that they're not and that Michael is correct above, but let's just assume they are.
So: I'll build a bunch of telescopes and "lasers" on the outer layer of my swarm, and I'll use about 0.000001% of my available power to continually scan the entire sky using automated systems, looking for threats. As a bonus, this system also gives me super awesome astronomy capabilities because it means I'm doing a continual full-sky survey. And I'm not even going to notice the resources it uses. So I'm actually really happy to do this even though I don't consider these objects a threat.
And if I find any threats, I'll use 0.001% of my available power to vapourise them with my "lasers" before they get within a few AU of any of my important stuff.
And to deal with the really big once-in-a-million-year rogue planets, I'll start working on the infrastructure for a stellaser so that I can put 10% or 20% of my available energy into vapourising stuff if I need to.
The point of Dyson spheres is that Dyson was a physicist, and he was trying to work within what physics seems to be telling us. So he didn't want to invoke magic. Thus no super-strong magic materials (no scrith) no super magic sources of energy, no FTL travel, no magic reactionless drives. That means civilisations are effectively trapped in the space around the star that gave them birth: it's possible they could colonise nearby stellar systems using generation ships, and they could even communicate with those colonies, given a round-trip communication delay of many years. But they could not trade on reasonable timescales or anything like that: the colonies would be entirely independent civilisations.
Given those constraints, if you want to keep your economy growing, a Dyson sphere (really a Dyson swarm, of course since no magic materials) is a fairly plausible end point.
(It makes me sad every time I have to say 'was' about Dyson.)
Dyson spheres are highly unlikely to ever be constructed anywhere. They would have a totally devastating impact on the climate of any planet orbiting the star, so are not a practical solution even if the means existed to make them.
I'm pretty sure that if we advanced to the stage where the construction of a Dyson sphere were remotely possible, we would have found far better & easier ways to get as much energy as we needed. Theoretically anything that has mass can be converted to energy, and a small amount of mass can produce a huge amount of energy. 1kg of any material (sand, rock, water etc) could be converted into about 25 TWh of energy according to Einsteins famous equation. Currently man's *total* energy consumption worldwide is running at about 160 thousand TWh per year, so if we could convert mass to energy we would need only arould 6300kg of any material per year. We just don't yet have the knowledge needed to convert mass to energy in a controlled way.
Dyson spheres are highly unlikely to ever be constructed anywhere.
They would have a totally devastating impact on the climate of any planet orbiting the star
They sure would, given that the idea is to use the raw materials from any planets to construct the sphere. And you'll need a whole lot more than one planet's worth if you want to capture all the light.
You also seem to be assuming "planets with biospheres", and the vast majority of planets aren't going to have biospheres.
...construction of a Dyson sphere were remotely possible, we would have found far better & easier ways to get as much energy as we needed
1. It's possible for humanity to build a dyson sphere today
2. You're assuming such methods exist.
Theoretically anything that has mass can be converted to energy
You're assuming that there's a way to do this with 100% efficiency and 0 joules input.
We just don't yet have the knowledge needed to convert mass to energy in a controlled way.
Again, you're assuming that it's possible. The equation says e = mc^2. It doesn't say anything about how efficiently you can convert it.
Thermodynamics, on the other hand, does. Hint: doesn't look good if you want 100% conversion efficiency. Sorry to burst your bubble.
"It's possible for humanity to build a Dyson sphere today"
How? You claim that a DS would use up most of the non-stellar mass in the solar system. Would that involve somehow mining Jupiter, Saturn, Uranus and Neptune into oblivion (if not then they would have a significant gravitational effect on the constructed sphere). The amount of energy involved in just getting a small robot lander onto the surface of Mars to dig up some rocks is very significant compared to the amount of Mars rock that will actually be moved.
A Dyson sphere isn't a single, stiff and solid mass. It only means putting something around a star to collect all the energy.
First you put up a few satellites in planetary orbit that do some useful work with the energy they collect from the local star. (Done!)
Then you start to put up satellites that beam the collected energy somewhere else.
Then you start putting those satellites into solar orbit instead of planetary.
Then you keep doing that.
Well, if Mark Zuckerberg reads the Register, you may want to hone your sales pitch:
Of course, Jeff Bezos may also be a reader:
Or even Bill Gates:
Although I must say, from bitter personal experience, starting to build something, and actually finishing it are two very different things.
You probably don't actually need a hundred billion. I suspect it might be possible to get started significantly cheaper than that. You might be able to make a pretty reasonable start with only a couple of billion. But I don't have a costing here in front of me, so I threw a number out there that should get the job done.
What you need to do is get enough infrastructure to an asteroid or maybe the moon so that you can start mining and building more infrastructure, which you can then start turning in to power collecting satellites and still more mining infrastructure. The seed resources actually required from earth are really not that high.
If someone wants to give me the resources to start work on a Dyson Sphere, I will gladly spend the rest of my life building that fucker and doing really not very much else. And I just might be the happiest person in human history while I'm doing it. Though I will insist on calling it something along the lines of 'The "AntiSol is a pretty cool guy" Thunderdome Stellarsphere' ;)
OK, for accuracy I should have said that it's possible for us to start building a sphere today. Actually dismantling planets would be a later-stage part of the process.
Richard 12 answers the how nicely. Though I would have added in a "you start mining asteroids and then progressively bigger bodies for materials" as one of the dot points.
"It's possible for humanity to build a dyson sphere today"
Really? Other than the lack of human industrial capability (by several orders of magnitude), how do you propose to get around the issues surrounding the net gravitational interaction with the englobed star? (See Shell theorem, if you're not familiar with the concept.)
> 1. It's possible for humanity to build a dyson sphere today
No it isn't. Talk about wishful thinking! Heck, we aren't even able to go to our moon right now, and you suggest we can tear down and rebuild our whole solar system?
And even if we had the technology, the materials and the manpower required to start, who would pay for that multi-century project (and how?)? Or do you suggest we might be able to finish moving the whole mass of the solar system around in time for the quarterly earnings report?
To resume, we not only lack the technology, but also the will and the coordination required.
The only way to say it might work is to conveniently forget all those real-world issues preventing it. Like other big theoretical notions (like "World Peace"), Dyson spheres are bound to shatter against Reality.
No it isn't
Yes, It is. The necessary tech all existed by the early 80s at the latest. Somebody didn't read the whole thread. Here's the basic HOWTO.
I never said the political will was there. I said it was possible in the technical sense. And it has been for decades.
who would pay for that multi-century project
Somebody didn't read the whole thread. It actually wouldn't be that expensive to get started. Bill Gates or Elon Musk could afford it and still live a very comfy life.
In fact it starts paying for itself relatively quickly because the vast majority of the necessary resources are essentially free once you get it seeded. And as an extra bonus, by the time you have it ~1% completed, you'll be the richest entity in history because you'll have pretty much solved that whole little energy thing for 4 billion years or so.
Dyson spheres are highly unlikely to ever be constructed anywhere. They would have a totally devastating impact on the climate of any planet orbiting the star, so are not a practical solution even if the means existed to make them.
Once you have the sphere you don't need the planet ;)
Assuming you can solve the gravity problem you have so much surface area to inhabit inside a Dyson sphere that the loss of one planet or a hundred, even a thousand is no big deal.
While nature can indeed produce similar pollutants than those that Man produces, in most cases it can only do so after there is significant macrobiological life on the planet (e.g. combustible vegetation), which while not indicating that sentient beings exist would at least show that life exists elsewhere.
Of course, you can't rule it out being artificial 100%. But the overwhelming balance of probabilities is it was natural.
If it was launched deliberately, then it was launched at a time when there only a few monkeys (or a few dinosaurs). And why would you send a probe to a nondescript system?
And if was just happenstance, what are the chance that the first extra-solar object we see is an alien probe? Unless there was a space war a million years ago and debris is regularly passing through the solar system, it would be a total fluke.
"If it was launched deliberately, then it was launched at a time when there only a few monkeys (or a few dinosaurs). And why would you send a probe to a nondescript system?"
If it was a natural object yes. But <devils advocate mode> if not a natural object, who's to say it wasn't travelling a hell of a lot faster and we only saw it after the braking manoeuvre ended? </devils advocate mode>
So, Mr. Devil's advocate, you're telling us the artificial body travels at ludicrous speed then slows down so we can see it tumbling in visual range and then, what ? I assume it will again accelerate at ludicrous speed to visit some other worlds. Question is, why bother will all this ? Would an intelligent civilization spend a hefty amount of ressources to send a probe to a galaxy far, far away only to have it back without even completing a single orbit around our beautiful planet ? Man, they're pretty quick aren't they!
In order to brake, one must point exhaust in the direction of travel (more or less, assuming ballsitic trajectories, which is approximately true outside of orbital dynamics and holds reasonably well for interstellar travel)
Such exhaust would promptly be lit up by the star you're braking towards and show as an "inverted comet"
A great place to go for cosmology stories ......
That paper's a great read. [Clicky, for PDF] It's only a page and a half, and you don't need anything more than A level physics.
(Caveat: crashing probes into visiting objects just so we can do a spot of spectroscopic analysis.is probably not a good idea if we think they might be aliens; even if they are friendly, it's not a good way to start a relationship.)
And Appendix A should be forwarded to a certain C Stross. There's one criticism in there I hadn't even thought of. (Ooops, we vaporised our light sail!)
The researchers are particularly interested in the technosignatures of a Dyson sphere, a hypothetical structure built around a star to harvest its energy. Scientists could detect these spheres – popularized by physicist Freeman Dyson – by inspecting the infrared spectra around stars to see if its heat was being funneled elsewhere, the paper suggests.
It's been known for aaaages that Dyson Spheres will have a characteristic look to them: lots of IR emissions, almost no visible light. In fact I'm pretty sure that we've even done surveys looking for them. So I'm not sure what's new here?
The lead researcher on the team, Avi Loeb, chairman of Harvard University’s Department of Astronomy, has argued that Earth has already witnessed the product of an alien civilization: ‘Oumuamua, the first-known foreign interstellar object to visit the Solar System.
Yeah, I've heard this theory before. It sounds real nice.
But if he's actually advocating that position with no evidence to back it up then he's about as credible a scientist as I am.
OK, yes, but joking aside: Department chairs are not necessarily particularly gifted researchers or theorists. A healthy academic department selects a chair1 based on administrative qualities such as management skills, organization, diplomatic skills, fairness (one hopes), and so forth.
Often "department chair" means "tenured faculty member who was seen as the least-bad compromise by enough of the faculty and hasn't yet pissed off the dean too much". Or, of course, "dean's toady", which is at least as common.
Loeb's other non-research qualifications are more significant, and even those should take a back seat to his actual research publication and presentation history, and how those have been received by the field.
And all of that, still, is hardly a reliable indicator. For exhibit A I give you Linus Pauling. Good chemist, lousy nutritionist.
1In the US, at least, the process for this varies by university and college, but is likely to be complicated and fraught. But usually the department members (at least the tenure-stream faculty, though at sensible institutions fixed-term faculty, staff, and even those scum graduate students may have some influence) get to at least vet candidates and create the final list of options.
Really the only feasible one is using the transit of a planet on its star to detect industrial gas emissions. Everywhere is too far away for radio, do the sums.
Indeed giant spheres and rings are probably just fantasy end of SF. James White's "Federation World" and Larry Niven's Ringworld. Niven had to have fantasy materials.
Also the scale is such that travel would need generation ships, robot probes or some kind of as yet unknown space folding star ship. Warp bubble drive is even less feasible than a ringworld. So there are no worries about invasions. By us or of use.
"Oumuamua, the first-known foreign interstellar object to visit the Solar System." No evidence whatsoever that it was fabricated. The likely explanation is a rock flung across space aeons ago by a natural collision.
Yes, we've known for decades what sort of signature a Dyson Sphere would have, The supposed three"levels" of energy utilisation/capture vs level of civilisation defined by Kardashev in 1964 are pure speculation. Really just plot fodder for SF. A really advanced civilisation might be argued to use less energy. The Kardashev scale and the two later additions reminds me of 1928 EE 'Doc' Smith's Skylark, because it's pure speculation. The start of Space Opera.
A complete Dyson Sphere would also require a couple of large rocky planets to be dismantled in order to provide just the basic building materials for the frame.
Any civilisation that requires even a meaningful percentage of a stars output will most likely be spread across multiple systems already and I struggle to think of any possible reason for that much usable power in just one place. The logic for building a D-S is the same as dropping a miniature 100MW power plant into every house on the planet - why make the effort?.
Much easier to build would be a simple network of orbital arrays* built to capture enough energy to power the actual requirements of a civilisation.
* Hundreds of arrays, covering several thousand square Km each in their own stellar orbit a safe distance away from the receiving planet (or mega station) completely invisible to our telescopes and easily scaled as required.
> I struggle to think of any possible reason for that much usable power in just one place.
Maintaining the consciousness of trillions of individuals, running on whatever substrate. Is one theory. Knowing nothing of the motives (or form) of a civilization with that much ability, it's as good a guess as any.)
If we decide that life is valuable, there are philosophers who suggest that we should have as much life as possible... there's lots of thought, discussion and argument in these areas.
"Any civilisation that requires even a meaningful percentage of a stars output will most likely be spread across multiple systems already and I struggle to think of any possible reason for that much usable power in just one place."
Well, if we want to use the 'gigantic space laser' method to propel a reasonably sized spaceship to another solar system then that amount of energy might come in handy.
Hang on a minute. On reading my above posting, I realise that I've seen lots of pictures on APOD* of stars emitting vast, high energy, high speed (respectable % of c velocity) 'jets' of matter. Our telescopes are as yet unable to resolve the starship and lightsail being propelled by those jets. Maybe the jets are evidence of interstellar travel and so of intelligent technically advanced life elsewhere in the galaxy / universe?
Thinks ... Nahh, don't be silly.
*Astronomy Picture of the Day, from https://apod.nasa.gov/apod/archivepix.html
Not to speak of the huge amount of energy necessary to dismantle a planet and turn it into usable materials or the dire consequences the disappearence of a small to medium size planet will have on the delicate gravitational dance of remaining planets. I surely wouldn't do this to my own planetary system.
A likely end-point of our civilisation is a nuclear war: I think the current most plausible trajectory is failure to deal with global warming leading to serious resource problems (at least water, probably also food) combined with catastrophic levels of migration with resulting awful politics, resulting wars over resources amongst nuclear-armed states escalate, game over. There are other scenarios which lead to the same end-point.
So, well, if we assume other technological civilisations have trajectories which end in the same place, then it would be interesting to ask two things: firstly whether the radiological signatures of a nuclear war are likely to be unique enough to be detectible, and secondly how long they would be detectible for. It's probably safe to assume that the technology of nuclear weapons is determined by the possible physics, so whatever they blew themselves up with will be similar to what we're going to blow ourselves up with. If you assume mildly similar geology etc (which again seems plausible to me) then it ought to be possible to work out what the signature would be and how long it will might be detectible (this depends on half-lives of things obviously).
It might easily be the case that most civilizations go through a period of ~ a century when they might be detectible while they're alive, followed by ~ ten thousand years during which their radioactive corpse might be detectible. So looking for the corpses would be at least interesting (and probably unsettling if we find a lot of them).
The paper doesn't seem to talk about this: I'd be interested if anyone knows of people who have thought about it.
I've also wondered how detectible nuclear flashes are: are they bright enough and unique enough that you could see them on exoplanets with some survey instrument? Obviously you'd have to be looking at a much larger volume of space to find them than you would to find the radioactive corpses they leave.
A tad pessimistic. There's no reason society has to go down the global nuclear war path, unless they active choose to by ignoring technological solutions to artificial and genuine resource scarcity.
Nuclear/solar/wind/whatever powered coastal desalination plants (and use the salts and minerals extracted instead of digging them up), vertical farming and greenhouses utilising hydro/air-ponics, for instance. All perfectly achievable right now, but relatively expensive so why bother.
We've seen over the past year what can be accomplished (albeit with varying degrees of success) given sufficient political will and scientific effort. Just need to turn that same zeal to resource production and management. Critically that's not biting the majority of the world yet, so these things just get talked about instead of acted upon.
But give it time. If things start to get desperate it's much more likely we'll invest in technological solutions than nuking each other into oblivian. The cost of doing nothing is far, far greater than the cost of fixing things.
Multiple nuclear armed countries with enough critical resource issues to contemplate launching nukes.
Hmm.. nuke and get nuked or...
We'll reach a civilised agreement to carve up the non-nuke countries between us into areas of influence and not ask too many questions about what the others are now doing in their new playground.
Humanity can limbo under any ethical bar however low you set it.
A tad pessimistic. There's no reason society has to go down the global nuclear war path, [...]
Yes, definitely pessimistic. On the other hand we have precisely no evidence for technological civilisations which last longer than 150 years, very good evidence that our current trajectory will do very bad things indeed within the next century, and very good evidence that, in the case of that kind of crisis our collective response tends to be, well, xenophobic in the extreme, let's say.
We may get away with it, and I'm certainly not competetent to assess the probability that we will or won't.
But looking for evidence of whether large numbers of other civilisations didn't would be useful, I think (if such evidence is detectable which I don't know). Apart from anything else if we were to find it we would have both an answer to the Fermi paradox and really convincing case that we'd better do something about where we're headed.
Any civilisation has to get through the Nuclear Squeeze.
At some point, a civilisation is going to figure out fissile chain reactions and/or fusion reactions.
One of the easiest things to make with any energetic reaction is a big badda boom, and so someone will do so.
The resources needed to make such boom are easily acquired and handled by a relatively small nation-state. If you can build a motor car, you can build a fission bomb.
Thus a civilisation is very likely to gain the ability to utterly destroy themselves while still divided into small nation-states.
The challenge then is to avoid accidentally or intentionally doing so - and to keep on avoiding that outcome.
It's not thechnology or science that we're lacking. We the human race lack empathy and compassion at planetary scale. Just look at how the rich countries managed to get ahead of the line in order to get vaccines, medical equipment, ventilators etc. when the COVID virus hit us. Medical masks and protective gear traded and hijacked by the highest bidder directly on the tarmac. And let's not talk about famine or the astronomical cost for a single treatment that can save the life of a human being (Zolgensma, priced at a hefty $2.1 million per dose - you'd better hope you don't need to take it three times a day).
It is not the resource production that will wipe us out, it's how we share and distribute those resources.
I would put oil before water and food on the list of resources that once they get close to exhaustion will bring down our civilization faster than you could spell atomic war. Try to imagine how much will cost the last drop of oil and what the countries will be willing to do in oder to get their hands on it.
> competing for the last of the fossil fuels
Hey, that could make a nice setting for a post-apocalyptic movie!
We could set it a desert landscape, and for the wow factor base the civilization on huge, gas-guzzling vehicles people use to fight and steal each other's last gas reserves (obviously burning more gas in the process than they could ever hope to steal)... I think you could nickname the hero "Mad" something.
Sorry, digression... But still, did they add "Thunderdomes" into the list of things to look out for?... :-p
"Try to imagine how much will cost the last drop of oil "
No need. oil is already at 1% of ease of extraction as it was 100 years ago and as the price goes up alternatives are being found
an "oil economy" is predicated on oil being the cheap energy source and that was only every going to be a short term proposition. Richard Milhous Nixon has a lot to answer for his actions in 1972 (as does Henry Kissinger, who in 1973 locked the _world_ into depending on oil for "world peace" by transforming the US dollar from being gold backed to "black gold" backed instead)
100 year sform now our descendants will look at each other and quizzicly ask "why did they burn stuff as fantastically useful as OIL?"
"firstly whether the radiological signatures of a nuclear war are likely to be unique enough to be detectible"
Fallout from weapons is both minor and shortlived. The long-term effects everyone worried about in the cold war (nuclear winter) was a result of many city-scale fires (Dresden/Tokyo, etc) carrying soot into the stratosphere where it can't be rained out in a short period of time
That's what I suspect too. But I wonder. What you want is some fission product which has a half-life of hundreds to thousands of years and also some very characteristic x-ray or gamma-ray signature for its decay. Then you could look for photons of the appropriate energies. The only other way it could have got there would be supernovae and that would all have gone away long ago for any kind of planet.
The problem would be that, even if such nice products exist from fission weapons, just by virtue of having long half-lives they would be emitting comparatively few photons. But, well, astronomers do amazing things, so.
The problem here as I see it is that we have been polluting in a way detectable from space for what, 200-300 years. In another 100 years we need to have reversed that trend, or we are unlikely to last much longer as a speces.
What this means is that pollution as we see it will likely only exist on other worlds for a relatively small amount of time (infinitesimal even) - for much the same reason. A long lived, mature civilisation will have almost definitely gone through a polluting phase and out the other side. Or am I missing something here?
A similar argument applies to radio signals. Human broadcasts from 50 years ago were easily distinguishable from noise. But modern digital transmissions are compressed, and the more efficiently a signal is compressed the more it resembles noise - any regularities indicate inefficient compression.
Since we consider the human race which inhabits the Earth to be a valid example of intelligent life, it can't be argued that industrial pollution isn't evidence of intelligent life.
However, scientists looking for intelligent life aren't just looking for life exactly like ourselves. So, an indicator of intelligent life that would only assist in finding the few worlds which combine the cleverness needed to build technology with the stupidity that allows polluting the planet with it is of limited interest compared to one more general that might actually find life more intelligent than ourselves.
>Since we consider the human race which inhabits the Earth to be a valid example of intelligent life
Well, relatively evolved life anyway. We remain violent and irrational primates who live in tribes which regularly try to wipe out other "competing" tribes, That and trashing our planet's environment. Perhaps we should stick to "potentially intelligent life" as the verdict is not in yet. Joke alert as I am kind of, half joking ;-)
Science Fiction has been exploring all of this for a long time. Which would be part of the problem if you were born after 1980. You haven't read all the scifi literature... (SciFi is the all about exploring what ifs. It is amusing how much computing was predicted, and how much wasn't...)
So, exploring this is good. The same things get invented/discussed over the years, and enhanced with current knowledge. This is how we advance.
"Looking for intelligent life? Have you tried checking for worlds with a lot of industrial pollution?"
Surely a lot of industrial pollution would be a sign of unintelligent life like wot we 'ave 'ere (ref. Monty Python). Truly intelligent life wouldn't be likely to make the poisonous mess we have (but maybe different mistakes and messes?)
As far as we know the only intelligent life needs free oxygen, O2, in an atmosphere. This was created by the very generous supply of cyanobacteria which produce this toxic gas as a bye-product of photosynthesis. O2 will readily combine with anything available, like Iron (this is where all those iron oxide deposits came from) so free oxygen in an atmosphere is highly indicative of some form of life.
The first gas to look for in our search for extra-solar intelligent life is therefore O2, followed by industrial pollutants such as lead vapour: you get that from smelting metals, but I don't know if it can be detected yet. Humanity has been smelting metals for over 6000 years, so the opportunity for discovery would be slightly longer than for say, atmospheric Chloro-Fluoro-carbons (< 100 years).
A rocky planet orbiting in the habitable zone but which appears to have an implausible, metallic upper-atmosphere. This would be a civilisation that fell foul of the Kessler syndrome.