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Comment by kentonv | Hacker News Reader

My pet theory (which is not intended to be taken too seriously) is that it is indeed a discarded light sail, and that light sail in particular was used to transport a Von Neumann probe which detached at some point after the object entered our solar system but before we first observed it. This detachment, in addition to leaving the sail tumbling, would have changed its trajectory, meaning our estimation of which direction the object originally came from is incorrect. In any case, the probe is now busy replicating, perhaps on the surface of Mercury. In a few years an army of robots will launch from there and invade the rest of the solar system!

Realistically, though, it's too much of a coincidence that such a probe would first arrive so soon after we gained the ability to conceive of it.

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Excellent page discussing the physics of colonizing mercury: https://einstein-schrodinger.com/mercury_colony.html

"Colonization of Mercury appears to be a very real and practical possibility, whereas colonization of Mars or the other planets, moons or asteroids is really more in the realm of fantasy."

A big advantage of Mercury over mars is higher light intensity: "One very important advantage is the high solar light intensity, which is stronger than on Earth by a factor of 10.6 at perihelion and 4.6 at aphelion"

Big disadvantage of Mercury is its depth in Sun's gravitational well. This is worse than planetary escape velocity, because you have to pay it on both ways (to get to Mercury as well as get back). Another problem is radiation which this close to Sun and with no atmosphere is pretty huge issue.

Light intensity is irrelevant. Energy in the form of light is pretty much free within solar system unless it is somehow obstructed. Free in that you don't need to take it with you and it is completely renewable. If you have less light you just gather it from a larger area. Mars has actually pretty good light intensity because it has thin atmosphere (it blocking much less electromagnetic spectrum).

For a colony much more important are parameters: how difficult and long to get there, how much need to be taken with you (ie. do you need to have water/air with you), how much protection you will need to live there (temperature, differences, atmospheric pressure, radiation, gravity, etc.)

Can you explain why you have to pay for the Sun's gravitational well on the way to Mercury? From the famous XKCD illustration[1] I get the impression that it might be hard to "stop at" Mercury since the pull of the Sun is relatively strong. Is there no clever trajectory that comes close enough to Mercury to get caught in its orbit?

[1] https://xkcd.com/681/

A better image (imho): https://i.imgur.com/SqdzxzF.png

You want to stop when you get to Mercury. In the XKCD illustration you have fallen quite a bit from Earth to Mercury and now have that as kinetic energy. You can dissipate that by hitting Mercury but that would likely have significant negative side effects.

Loosing the energy on Mercury is only part of the problem. You also have to get there.

Contrary to popular belief, going closer to the Sun is as much difficult as going further away from it. Orbits require energy to change them regardless which direction you want to do it. You can go to tables and see going to Mercury costs almost the same as going to Jupiter: https://en.wikipedia.org/wiki/Delta-v_budget

There are handy maps of Sol system if you are interested: https://forum.kerbalspaceprogram.com/index.php?/topic/131682...

You can of course minimize the energy even further using gravity assists, but this would require multi-year journey.

There is another trick when you want to go very close to the Sun, which is to go further away first, and then use much less energy to actually stop your orbital speed and fall however deep into Sun well you want. Unfortunately, Mercury is just far enough from the Sun to make it unprofitable and it also takes an awful amount of time to execute.

I think Randall's image is a bit misleading. I mean it is correct and fun, but for an uninitiated person it might cause impression that going down the well costs zero energy.

That of course is true, if you are stationary. Then you just start falling like apple from apple tree. But almost no objects in space are stationary, typically everything orbits something and frequently multiple things at the same time. Think about a rocket that is on an orbit around Earth. It is not free to fall to Earth, it must expend delta V to slow down enough so that its perigee is within Earth atmosphere (and typically well within atmosphere or it will just bounce off it).

At the same time, the rocket orbits the Sun, so even if it leaves Earth it still is not free to "fall" into Mercury. It must expend delta V to slow down so that its perihelion lowers at least to Mercury orbit.

So the graph on xkcd is correct, but with regards to bowling balls you might want to shoot up or let fall down from a position that is stationary in some celestial body's frame of reference.

Cool! Personally, I like the idea of building a Dyson swarm out of it (sorry Mercury!) https://www.youtube.com/watch?v=pP44EPBMb8A

Kim Stanley Robinson wrote a book, 2312, which featured an equatorial city on Mercury mounted on massive concrete rails.

The expansion of the concrete rails on the day side permanently keeps the city in the planets relatively pleasant pre-dawn zone.

The city only needed to move at walking pace to stay ahead of the sunrise.

IIRC one of the major mercurian industries was maintaining massive solar reflectors that were used to boost light going to specific asteroid greenhouses.

What if the city would have engine trouble, though...

It had no engines. The sun-side tracks thermal expansion provided the energy to keep pushing the city into the night-side.

Which forces the logical conclusion that this isn't the first such probe, obviously.

That could only be true if they are intentionally hiding from us, rather than replicating and harvesting the solar system as fast as they can. But personally I have a hard time believing that hyper-intelligent devices would care about avoiding detection by lowly biological organisms like us.

Someone asked this once and now I can't stop thinking about it:

There's so much good stuff out in the Oort cloud, why would you ever bother climbing down the gravity well, let alone attacking the poor primitives most of the way down it?

A more likely "War of the worlds" scenario would be someone mining the outer solar system to bits and leaving without us being able to throw so much as a rock at them. If they take enough, even our ability to hunt them down for revenge would be significantly hampered.

Speculating about the motives of a species that may or may not be biologically similar to us and which, even if they are similar, may well be millions of years more advanced than us is very hazardous. I think these kinds of speculations lead many people to hold all sorts of strongly held but unfounded beliefs about what ET's may or may not do here.

Maybe after another million years of development a species' main motivation would be simple curiosity, in other words they are basically scientists. Scientists may want to avoid interfering with a species they are studying and therefore remain hidden. But then the same scientists conducting a different experiment may want to selectively perturb the specimen's environment to probe their psychological reactions and degree of intellectual development.

Exactly, the classic Terran (of the norm), functions mainly with the help of cognitive biases and other syndromes preventing him, by social cohesion, to admit other tunnels of reality than those that composed their groups (majority currently) It's a pity, with a brain so powerful, if you knew what you could understand, admitting to omit the permanent self-awareness.

Exactement, le terrien classique (de la norme), fonctionne principalement à l'aide de biais cognitifs et autres syndromes l'empêchant, par cohésion social, à admettre d'autre tunnel de réalité que ceux qui ont composé leurs groupe (majoritaire actuellement) C'est dommage, avec un cerveau si puissant, si vous saviez ce que l'on peux comprendre, en admettant d’omettre la permanente conscience de soi.

If this is a quote, how can I read the rest?

https://arxiv.org/abs/1302.0606 MAD with Aliens? Interstellar deterrence and its implications

Just from reading the abstract that looks extremely speculative. Frankly you might as well try to make inferences about human behavior by studying aggression in bees.

If the mission of the probe is exploration then it doesn’t need to consume all of the resources of a solar system. It just needs enough to make a few copies to reach the nearest handful of stars. If they are using light sails as propulsion they probably need barely anything. I don’t have a hard time believing that an advanced civilization would choose hiding as the default method of exploration. Anything from the dark forest to the prime directive could be used as an argument to do so. I agree with the other comments that it’s fairly likely that our system has had multiple probes pass through. The unlikely event will be when one decides to contact us.

While it's entirely possible they'd have a good reason to be stealthy, I don't think it's likely to be anything we've thought of.

The Prime Directive is a mushy human emotional idea, not something that makes any logical sense for a space-faring civilization to follow. If there's any competition out there among space-faring civilizations, none of them are going to tie their hands behind their backs by refusing to touch planets that have native life on them.

And under the Dark Forest, the best way to survive would be to replicate as fast as possible, consuming all available resources. They would want to hide from external, more-powerful civilizations, but they'd have no reason at all to hide from us. Hiding from us would be a strict loss for them, as it means they can't mine Earth for resources.

What you are missing is that technological advancement can accelerate exponentially. Couple this fact nothing can move faster than light. This means if you don't stamp out alien life as soon as you encounter it then the next time you come back they might already have achieved technological parity with you. And they might not be as forgiving as you are. This means you have to hide and you have to exterminate any alien life that knowns about your existence. I do think if oumuamua was an alien probe then we should be gravely concerned.

> the next time you come back

This is imagining that space exploration is done by human-like entities that have discrete physical bodies and slow reproduction rates. They come to a place, check it out, and move on.

AI-driven Von Neumann probes would operate very differently. They arrive, and they settle and replicate. Eventually they send out new probes. But they don't leave once they have arrived. There's never any reason to leave.

Okay the point is you won't wait to mobilize against alien life. Assuming that technology increases exponentially it will be prudent to launch as soon as you detect the alien life even if it takes you a hundred years to reach the destination.

I’m not sure that reasoning holds up. There’s no reason to believe that “mushy human emotional ideas” are not the norm. There’s no data to support that claim since humanity is the only example we have of intelligence. So for the sake of the argument I’m going to define alien intelligence as similar to human intelligence. I’d also inquire what the point of having a Von Neumann probe consume all of a system would be? It’s not practical to ship the resources anywhere at sub light speed. There’s a limit on the number of probes it would be rational to make in any one system even if you were going for high redundancy. Even use as a weapon would be foolish since there’s a good chance something could go wrong and you’d wind up killing your own systems. Maybe if you were paving the way for a colony but even then you’d only build what you needed to avoid having to constantly maintain the structures until they were useful. The only way I see an exploitive strategy working is if you have FTL travel and if you have that then Von Neumann probes are useless old technology since you would just send a fleet of ships with what you need to get started rather than trying to bootstrap from a single self replicating probe.

Once a civilization is capable of building Von Neumann probes, it would be silly for them not to do so. They are basically free, since they are self-replicating. Of course a civilization is going to want to control and harness as many resources as it possibly can. We may not be able to imagine what they'd want to build out of whole star systems, but I absolutely don't believe that civilization will ever run out of things to build.

If there's any competition between civilizations, then it's even more obvious that each one will be racing to claim any star system that isn't already claimed. But even with no competition, it makes sense to spread rapidly.

If you don't find that intuitively obvious, consider this: In 4.5 billion years, the Milky Way will collide with Andromeda. This presents us with a literal galactic-scale single-turn prisoner's dilemma: If intelligent life exists in Andromeda, they may already be preparing to conquer the Milky Way. If they are, and we don't prepare to fight back, they will obviously win. We won't have any ability to communicate with Andromeda to find out their intentions until it's too late. The earlier we start preparing, the more likely we are to survive.

So if I were a spacefaring civilization in the Milky Way today, I'd be doing everything I could to mobilize every star system in the galaxy in preparation to beat Andromeda. There's just no reason not to...

Why do you want to "beat Andromeda"? You have your Von Neumann probes, they have their own. Maybe theirs are better. Why do you want yours to beat theirs?

“Of course a civilization is going to want to control and harness as many resources as it possibly can.”

This may be an entirely human-centric assumption. Maybe there are a million civilizations out there living in balance with their local planetary environments, entirely without the expansionist curiosity and destructive drive that leads humans to seriously contemplate things like von Neumann probes?

The desire to survive and expand is not a human trait, it is a natural result of evolution. Any successful evolved species will have this desire because those that don't, don't get anywhere.

Interstellar civilizations are unlikely to be biological, but evolution still applies. All it takes is for one civilization in the whole galaxy to decide to build Von Neumann probes, and they'll have taken control of all unoccupied systems in the galaxy in short order.

Is it? Evolution itself seems like an expansionary process but it doesn't seem to follow that the outcomes of the evolutionary process are expansionary. It seems like many species are evolved to very specific environments like caves or thermal vents that they will stay in for generations if not for thr duration of their existence as species.

> In 4.5 billion years, the Milky Way will collide with Andromeda. This presents us with a literal galactic-scale single-turn prisoner's dilemma: If intelligent life exists in Andromeda, they may already be preparing to conquer the Milky Way. If they are, and we don't prepare to fight back, they will obviously win. We won't have any ability to communicate with Andromeda to find out their intentions until it's too late. The earlier we start preparing, the more likely we are to survive.

I'm trying to imagine what to do now in preparation for a hostile encounter in 4.5 billion years that isn't already happening organically. By "organically", I mean both "in the course of gradual or natural development" and "w.r.t. living matter", given the time scale.

Do you have ideas?

That's self destructive behavior on a planetary scale. No species that has an instinct or culture to consume all available resources will survive long enough to do it on a galactic scale.

Also, the math doesn't work out in the sense that if a species that had this instinct reached interstellar travel a million years ago the Milky Way galaxy would already have entirely been consumed. That's the Fermi Paradox in a nutshell.

If the species you are describing exists, they must have just started eating the galaxy, because the galaxy would already be eaten in an blink of an eye on the cosmic timeline.

Lets suppose that it takes a ten thousand years to reach a star system and consume it, and the swarm needs the resources of an entire star system just to build 2 more probes.

That means that the number of star systems consumed doubles every ten thousand years. At that rate it takes no more than 50 generations, or half a million years, to consume the entire galaxy.

Note that if the number of probes the Von Neumann swarm builds is more than 2 per star system consumed, this process happens even faster.

Right, this is why I don't actually think the object is a probe: if there is no competition, then a million years from now, we can expect Earth-originating technology will have spread across the galaxy. To imagine that another civilization exists but is no more than a million years ahead of us seems like too much of a coincidence.

>That's self destructive behavior on a planetary scale. No species that has an instinct or culture to consume all available resources will survive long enough to do it on a galactic scale.

Have you ever read Issac Asimov's story "The Gentle Vultures"?

You should really read The Count to the Eschaton Sequence by John C. Wright. The Cold Equations is another answer to the question you pose.

Andromeda has 3-4 more stars than the milky way; we already lost, should we flee instead?

The odds favor Andromeda, yes. But depending on just how rare intelligent life is, there is some possibility that we have a lucky head start.

As for fleeing: The whole concept of "fleeing" assumes a civilization composed of discrete beings that are expensive to reproduce but can be feasibly transported. The idea of Von Neumann probes is based on a different assumption. The probe itself is very small, maybe only a few pounds, but is designed to expand using the resources at its destination. There probably aren't discrete beings -- computers can freely exchange "memories" over networks which makes them effectively all one big hive mind. The hive mind directly controls everything it builds. Eventually the entire star system -- perhaps the entire galaxy or universe -- becomes effectively one giant intelligent being as all available resources are assimilated.

This civilization would certainly send probes to neighboring galaxies if it has the ability to, but it makes no sense to think about transporting the "inhabitants" (if you can even call them that) of one star system to another en masse.

I wonder whether once a civilisation reached that point, the game theoretical equations around aggressivity and self preservation change significantly to invalidate the dark forest theory.

Consuming all available resources and destroying all competing life doesn’t make sense even for us as the dominant species of a single planet.

What’s the evidence that wholesale environmental destruction is a good idea on a galactic scale if it’s already known to be a terrible idea on a planetary scale?

It's a terrible idea for humans on our planet because we are squishy biological beings whose life is intrinsically dependent on the biosphere around us.

Self-replicating hyper-intelligent artificial beings presumably will be able to redesign themselves to match any target environment.

Note: This is not a moral judgment. I obviously think it would be awful if some AI gray goo consumed the universe and wiped out all the unique forms of life. But I think that's a rather human value and I don't see why the AI would share it.

Here's the problem. It would be astoundingly unlikely that we would still exist if such a civilization existed.

For this to have happened, it must have happened much less than a million years ago, otherwise your hypothetical civilization would already have easily consumed the entire galaxy.

Since we are still here, if that civilization exists, it must have arrived on the interstellar scene less than one quarter of one tenth of one percent (< 0.025%) of the age of the solar system ago. That seems like a crazy unlikely chance.

This is the fundamental problem with Von Neumann probes / AI grey goo in general : They eat the galaxy way, way faster than anyone can imagine. If they exist, why are we still here?

We commonly consume most available resources and try hard to destroy much competing life... in a given part of what we consider as our territory (our planet), for example when establishing then maintaining/growing a city.

Earth may be part of what an alien species consider as their territory.

What resources does Earth have that wouldn’t be more plentiful elsewhere? Minerals are cheaper to extract from asteroids (no gravity well). If I have the ability to cross interstellar space, then I can’t imagine that water is even worth that much.

Sweet sweet human flesh...

Regarding the prime directive as a mushy human emotional idea. I don't think it's unreasonable for some advanced society to see preservation of newly encountered life as a worthy goal even as a selfish motive. How many new ideas and ways that nature solves problems are we still learning just from the life on earth?

No, they're currently terraforming Earth¹ to have a CO2 level that is better for their metabolisms.

¹ through influencing politicians and the rich and powerful to keep poisoning the Earth with extreme pollution.

The politicians and rich and powerful are the aliens.

https://www.google.com/amp/s/www.indiewire.com/2014/10/john-...

I so thought that was going to be a link to The Arrival.

In case there are some younger non Trekkies not sure what the Prime Directive https://en.m.wikipedia.org/wiki/Prime_Directive

Those are not the only two options.

Besides, we still routinely fail to spot asteroids until they get close to Earth or pass by.

There may be more dwarf planets like Pluto, or a major planet the size of Neptune (per Caltech researchers, so called Planet Nine or Planet X) in our own solar system and we can't easily find them.

No need to intentionally hide from the primitive humans that are still struggling to locate large objects in their solar system and near their planet.

The existence of other planets doesn't seem to explain why they wouldn't colonize Earth. I would expect them to go everywhere.

What would the point of going everywhere be?

Maximize resource collection and manufacturing? Surely there's usefulness in raw materials.

To harvest all available resources in the service of whatever higher goal the civilization has.

Agreed. I don't sneak up on the ant colony that's become too close to my house before I dispatch it.

They?

She

Hmm...She!

(We are)

That reminds me of the books We Are Legion, We Are Bob.

I really enjoyed those!

Book 4 is on preorder now, drops in September.

> Realistically, though, it's too much of a coincidence that such a probe would first arrive so soon after we gained the ability to conceive of it.

It is based on TIME but our conception of it would be independent.

I think a lot of what's part of the drake equation is merited on overlap. It's entirely possible that other civilizations have been created and died out LONG before mammals even evolved.

IF you factor in just the last 200 years of human technological advancement it's plausible in another 200 we will have either destroyed ourselves or evolved into gods.

Either way we're not going to be talking to anyone in the universe.

I think it's plausible that a god would not want to talk to another intelligent civilization. Why would we? We would be to a god what bacteria is to us.

I don't really have a conversation with the bacteria infecting a wound. I just take antibiotics.

I don't really understand what this "evolving into godhood" means, but I would really like to talk with the bacteria if I could, even if I might still take antibiotics after talking to it.

> I don't really understand what this "evolving into godhood" means

Not dying of old age or saving your memories/consciousness into a computer and transferring into another body.

> I don't really have a conversation with the bacteria infecting a wound

Could it be because you know they won't reply? That's the case with most animals. Talking to a random dog or cat (relatively intelligent creatures) and knowing they don't understand a thing you say just kind of makes it pointless. Of course they'll understand simple universal body actions and react, but nothing more.

If there was a bacteria or a cat who would reply back, or at the very least clearly understand what I'm saying, I'd be happy and amazed, and definitely would want to continue talking to them.

What if an AGI’s intelligence has exploded to a point where human intelligence is insignificant?

it's based on what we understand as being intelligence so what would that even mean?

> I think it's plausible that a god would not want to talk to another intelligent civilization. Why would we? We would be to a god what bacteria is to us.

That may be because we can't even perceive bacteria, but if we go a little bit bigger and you could have a conversation with a dog, cat, deer, or any other animal, I bet you would. I know I personally would just to understand how those animals think and the differences between them and us.

With that said, I do agree with you, but I don't think this is really a comparable analogy though because I'm sure a god wouldn't want to converse with us due to boredom of interacting with plenty of other intelligent life and pretty much everything else before reaching us.

It's hard to conceive of an intelligence as much above ours as we are above bacteria cell. But if such a thing did exist why would it want to communicate with us?

If I could talk to cell(s), morphogenesis would be my topic of discussion.

> I think it's plausible that a god would not want to talk to another intelligent civilization. Why would we? We would be to a god what bacteria is to us.

At that level of abstraction it might make more sense to think of humanity itself as an organism, and to their point of view an infant one. At the point we either either birth an AI or elevate people to digital organisms with vastly greater intelligence, then we've "matured".

There's still reasons for adults to talk to or help adolescents, mainly to help them mature well, so there might be reasons for "gods" to talk to us.

It might also be that we're only at the stage of speaking gibberish, so there's still a bit to wait.

maybe we are just "ants" for them. That would be the current intelligence level of humanity for aliens.

Doesn't the cities, human civilization on Earth feel like a big messy anthill?

All our society could feel for them just like what we see when we look to what ants have built.

"Nice engineering down there, they communicate using sounds and directed energy, nice they've discovered electricity, they solve their conflict using mostly primitive kinetic weapons. Hey they have developed shows to fill the free time they've got now after having setup some automatization. And now they have a planet reaching data network, how nice.

They're quite aggressive tough, I wouldn't put my finger in there, they bite, hard enough"

I don't expect ants, either as an individual ant or as a colony, to necessarily be able to hold a conversation given enough time, but an alien species more advanced than us, or a godlike AI, may expect at some point in the future we might be able to, or might birth something that is able to (if not, where did they come from?), which is why I think they would be more likely to view us as infants currently incapable of conversing with them usefully rather than bugs with no hope of doing so.

This is clearly a visitor from Bajor.

https://memory-alpha.fandom.com/wiki/Bajoran_lightship

Mercury provides solar power but you need a lot more energy to get from there to earth. The asteroid belt still provides adequate solar power with I'd guess an easier ability to 'fall on the earth'. It wasn't clear whether the goal of your invader was destruction or takeover. Falling rocks would do the destruction job.

The point is obviously more probes. I think a sufficient gravity field and planetary mass is going to let you work a lot faster. Robotic probes with basically no atmosphere to get through means you can use kinetic cannons to get off-world.

Your initial "factory line" would be a mostly underground equatorial band on Mercury.

Maybe, but the trajectory of the object seems more consistent with having dropped someone off at Mercury, not the asteroid belt.

My theory was it's the Super Dimension Fortress Macross and we can expect a Zentraedi invasion Real Soon now.

> it's too much of a coincidence that such a probe would first arrive so soon after we gained the ability to conceive of it.

Perhaps they observed I Love Lucy and Gilligan and came by to complain about spectrum pollution.

I don't think so. Light sails are not fast. It would have taken the probe millions of years to get here.

> Realistically, though, it's too much of a coincidence that such a probe would first arrive so soon after we gained the ability to conceive of it.

Are you sure it's a coincidence? Imagine you are an intergalactic species that advances yourself by invading other worlds and stealing the inhabitants' knowledge and technology. What would be the best time to invade? I would suggest waiting as long as possible in their technological advancement but just before they develop the ability to defend themselves.

Light sails are not very fast. The probe would have had to have been launched thousands of years ago at least, maybe millions. Either way, long before our current level of advancement could have been predicted.

I'd argue development isn't linear, as we seem to have millennia with pretty static tech, then in the span of a (increasingly long) lifetime, electricity, flight, and the internet. On that scale, our last 150 years could have occurred randomly at any time.

> as we seem to have millennia with pretty static tech,

That's not even remotely true. Even between antiquity and middle ages there were constant technological improvements. Of course everything sped up once we had access to steam and later fossil fuels as machinery to replace manual work became a reality.

Would a species that has mastered intergalactic travel really have anything to learn from us? I think they would either kill us, eat us, enslave us, or maybe all of the above.

you forgot another real option, "ignore us", just like we ignore ants when we walk around.

Or "blow up our sun before we can get uppity" - 3 Body Problem.

Shit happens, as in https://en.wikipedia.org/wiki/Code_of_the_Lifemaker

The prologue is sufficient http://www.baen.com/chapters/W200203/0743435265___0.htm , the rest is a matter of taste.

Personally I found it to be hilarious :-)

I thought one of the main issues arising with the "alien tech" theory is that this object was moving too slowly to ever make it to our solar system in any timely manner? Thats not to say it couldn't have slowed down prior to us finding it, but if its a detached light sail why wouldn't the alien probe have detached it at higher speeds to have less mass to slow down?

The probe would have needed to use the light sail to slow down as it approached the target star.

Really, the opposite is a better argument: How could the probe have landed safely on Mercury (or wherever) after ejecting from a light sale that still had enough velocity to escape the solar system?

> Realistically, though, it's too much of a coincidence that such a probe would first arrive so soon after we gained the ability to conceive of it.

Alternately, this implies that we're visited all the time, but usually by robotic probes flying through the solar system for brief visits before being disposed of responsibly and cleanly.

> it's too much of a coincidence that such a probe would first arrive so soon after we gained the ability to conceive of it

We've gained the ability to conceive of complex stuff only some thousands of years ago. Everything is "too soon" on that scale.

...and also first arrive so soon (comparatively speaking) after the publication of The Mote in God’s Eye — an excellent novel by Larry Niven whose plot starts with the arrival of a light-sail powered tube.

I thought you were going to say that’s the the discarded lightsail from a probe that’s thousands of years old, and all we were never the target of it. It’s just space trash now.

Speaking of pet theories, here is mine: There exists a sentry system of interstellar buoys that get sucked into star systems passing by. Perhaps with a solar sail, so they can control a bit which stars they want to take a closer look at. Our solar system become "recently" a candidate for obvious reasons. The probe made its analysis and plotted a fast escape, sending a tight laser beam to the next closest relay station. A fleet of planet biosphere erasing machine intelligence dispatch is on its way. Probably some ancient left over from AIGs engaged in eternal warfare. Hence a dead silent galaxy, a rather dark forest.

Or, in other words, the main plot line in the Inhibitor trilogy within the Revelation Space series by acclaimed sci-fi author and astrophysicist Alastair Reynolds. https://www.goodreads.com/series/56392-revelation-space

Ha! Thanks for the reading tip. I was unaware.

Sundiver:

Egg sac for a species of star-dwelling creatures. Hopefully they didn't arrive from Betelgeuse...

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