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Comment by jonathankoren | Hacker News Reader

The premise of the DFH is just so bizzare. Essentially godlike aliens go around killing other aliens for hell of it. It'S fOr SeLf ProTeCtIoN! Please. If you're a godlike alien, you don't actually have to care about anyone else. Hell, not only do you actually have to deal with intergalactic distances, we're talking about a plan that requires at this point quadrillions of individuals to be dedicated to multiple 100,000 year plans of preêmptive genocide against literally unknown civilizations.

I'm sorry. But I'm not supposed to suspend disbelief for serious discussions.

The older I get, the more I find these debates as tedious as medieval demonologists wondering about how many angels can dance on the head of a pin, and who is the fifth viscount of the third circle of Hell, and just what exactly is his bailiwick.

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> Essentially godlike aliens go around killing other aliens for hell of it. It'S fOr SeLf ProTeCtIoN! Please.

Isn't the point the point that they aren't godlike? They're glass cannons, capable of creating weapons with incredible power, but incapable of defending themselves against that same class of weapon.

Maybe the disconnect is the word "godlike". A truly godlike power wouldn't care, because they're beyond threat. But imagine something more like the cold war: Powers capable of mutual destruction, but not godlike.

In the aftermath of World War II, John von Neumann advocated a preemptive nuclear first strike on the Soviet Union before they could develop their own nuclear weapons. It's monstrous, but it's the same cold logic that the DFH proposes: Destroy others before they have a possibility of destroying you.

I think that's a useful analogy but I would say that it also implies limited DFT.

Von Neumann's plan was based on an incredibly short time scale. It wasn't long before the Soviet Union would develop its own weapons. The power asymmetry was only briefly held.

The thing is at a universal scale that would imply that the only threats we would honestly face are ones in close power level, and we can barely leave the earth at the minute. Another species with more advancement than us would be n-years more advanced than us even after we reach the level of what they were at on first encountering them (unless they decide to share technology which would be the opposite of DFT). Technological stagnation could cause a catch-up but then the theory has to assume technological stagnation is incredibly common for enough length of time to allow upstarts to catch up.

Now history has shown that more powerful nation's have conquered others. The 19th century is choked full with examples. That primarily was driven by competition by world powers seeking ever more resources for that competition. The universe is abundant in resources however, we have a lot to pick from once we are space faring species.

>Now history has shown that more powerful nation's have conquered others. The 19th century is choked full with examples. That primarily was driven by competition by world powers seeking ever more resources for that competition. The universe is abundant in resources however, we have a lot to pick from once we are space faring species.

We can model this using just exponential growth and fixed speeds. If civilizations with interstellar capability existed prior to now, we'd see them. The galaxy would be literally teaming with them. That's the Fermi paradox. That's what the Grabby Aliens paper explored.

They don't exist.

I use the word "godlike" because of just the magnitude of the energies and timescales we're dealing with. Drawing analogies with contemporary technology and behaviors really understate the magnitudes we're talking about.

Let's assume these aliens are dealing with just well understood Einsteinian physics. Nothing theoretical like wormholes, or thing. Their weapon of choice, is the same weapon of humans million years ago -- throwing big rocks.

Now, finding the mass of asteroids online is pretty difficult. It seems like most asteroids aren't actually measured, because the distribution of mass is highly skewed towards the Ceres, but two I'll look at are: 10 Hygiea, with 8.32E19 kg and 101955 Bennu (of OSIRIS-REx fame), at 7.329E10 kg.

Now we don't need to blow up the Earth Alderaan style. Instead, we'll aim for a Chicxulub impact, which apparently released something close to 4.2E23 J.

We'll also be pretty conservative about where aliens are, and assume they share our galaxy. This puts them at most around 100,000 light years away (the diameter of the Milky Way).

Let's say that we're accelerating our rock to 1% the speed of light. That means it would take 10 million years to hit your target. To put 10 million years into perspective, that's roughly how long ago chimpanzees and humans diverged. You're literally shooting at a species that probably won't exist, to protect your own species, that also probably won't exist.

Accelerating Bennu to 1% the speed of light would require 3.74E32 J and give an impact energy of 79x of Chicxulub. Hygiea at 1% would require 3.74E32 J be 900 million times the size of Chicxulub (8x the Great Impactor Event that birthed the moon). To put this in perspective, the Sun generates 3.8E26 J per second. You'd need to capture the entire output of the Sun for a day at 100% efficiency to accelerate Hygiea to 0.01c. Bennu takes a modest .0009 seconds of solar output.

10% the speed of light? 3.77E34 joules for Hygiea (9E10x Chicxulub) and 3.32E25 joules for Bennu (8x Chicxulub).

Just for giggles, 90% the speed of light gives 9.68E36 joules (800 years of solar output) to accelerate Hygia (2.3E13 Chicxulub, or 2 million times of the energy released by Great Impactor Event that formed the moon) and 8.52E27 joules (2.25 seconds of solar output) for Bennu (20000x Chicxulub). In this case, we'd be atomizing the planet in around just over 100,000 years.

On the other side, if we yeet these rocks at the speed of Voyager 1 (0.00005c, or 17000 m/s), it would take 2 billion years hit, and we'd get 20,000 Chicxulubs from Hygiea at the cost of 9.36E27 joules (2.5 seconds of solar output), and Bennu wouldn't even come close to Chicxulub, but rather a mere 4000 Tungustas at a cost of 8.25E18 joules.

If we want to cause 1 Chicxulub in 10 million years, we need to fire a mass of 1E11 kg, using 4.5E23 J of energy.

This is of course assuming that we're able to hit this planet without any course corrections. A planet mind you, we probably couldn't even theoretically image given the vast distances, infinitesimal angles, and the paucity of reflected photons that hit our telescopes. But hell, maybe we can develop some massive explosive or something that can last 6 million years to redirect our rock as we get closer to the system. The fact that we have to design an autonomous command and control system to last 10 million years in interstellar space is quite a lift, but let's just assume we get lucky.

Here's a spreadsheet of my work https://docs.google.com/spreadsheets/d/1_W_mJ1ev1mkvZZMkwVlJ...

References Wikipedia for masses and diameters https://www.omnicalculator.com/physics/relativistic-ke https://www.centauri-dreams.org/2012/04/13/collisions-in-the...

I admire your commitment to this discussion :)

In the Three Body Trilogy, the hyper-advanced aliens use projectiles accelerated to very near the speed of light. The premise is that there's enough energy in these that their impact is an extinction-level event for the planet they hit.

There's a fun thread on Quora[1] about so-called "relativistic kinetic kill vehicles", with the top comment making the good point that a small projectile moving very fast might just punch a clean hole in the planet and keep going, thus not transferring most of its energy.

[1] https://www.quora.com/What-are-Relativistic-Kinetic-Kill-Veh...

>I admire your commitment to this discussion :)

Oh god. I made a fucking spreadsheet! @_@

I had been thinking about aliens, von Neumann probes, and even giant super computers to simulate the universe recently. I've come to the conclusion they're all absurdly dumb like a pulp scifi story.

People always think these shots are one and done, but they’re not. You have to keep hitting the planets with extinction level events, and you have to do it before you detect a civilization simply because of the transit times. If for sake of argument, we assume the dinosaurs were murdered, how did that work out for the trisoleans?

>There's a fun thread on Quora[1] about so-called "relativistic kinetic kill vehicles", with the top comment making the good point that a small projectile moving very fast might just punch a clean hole in the planet and keep going, thus not transferring most of its energy.

I saw something similar about a microblackhole or strange matter or something like that. Basically, you wouldn't even notice unless you standing right under/over it. Then you'd have a bad time.

The alien's desire to destroy other civilizations is what drives the plot forward. The message that I took away from the novel was not what aliens care about, but that blind reliance on technology will not solve all problems.

Likewise debating angels dancing on the head of a pin, as if it were literal, wasn't the point. Depending on what sources you check it was either a made up story to mock scholars wasting time or a practice topic for debating.

Demonology is a “study” conducted by true believers for hundreds, if not thousands of years.

Someone sat down in the 13th century, and earnestly questioned whether Forneus was a marquis or earl, and whether 30 legions of demons under his command was too many. (It was. He has only 29.)

https://en.wikipedia.org/wiki/Forneus

An easy illustration.

Godlike aliens -> humans.

Other civs -> wasps, mosquitos, cockroaches. Not a real existential threat, but enough of a nuisance. Wasps, even though they live in a complex culture from their point of view, have no chance to understand human culture. Not wanting to be accidentally stung sort of has a chance to be understood by both sides, very-very approximately.

0. Wasps are everywhere (on the planet) and they can't destroy you.

1. Wasp-Aliens are everywhere in the universe.

2. Therefore they know how to travel with some speed v.

3. Therefore they know how to accelerate objects to speed v.

4. They can launch said objects towards your planet.

5. Therefore they can destroy you, so assumption 0 doesn't hold.

The DFH doesn't claim that the aliens would be "god-like" per your definition. They just have a first-strike capability and motive to use it. Could be a low risk-tolerance for coexisting with other aliens. Or something else. Either way, you don't have to suspend disbelief because you're arguing with a strawman you created.

I don't think you actually considered the energies and timespans required (let alone the political will) to yeet a rock at an unseen planet on the other side of the galaxy.

At 1% the speed of light, it will take 10 million years just see if you hit anything on the other side of Milky Way. If you have to wait 10 million years, why do you even care? You'll be extinct, as will your target.

Even if you do decide chuck a dinosaur killing sized boulder (which, really is probably the smallest you'd want to use), you'd have expend 4.5 * 10^23 joules just to accelerate it. That's equivalent of all the solar radiation that hits the Earth over five days. That's a huge lift for even a supposed Kardashev I civilization. It's something more practical for a Kardashev II civilization. Although to be fair, the practical threshold is probably somewhere between I and II. And let's be clear here. If you're dismantling planets to build mirrors, you're Galacticus.

Anyway, how would the decision to throw a rock across the galaxy even work? A civilization obtains Kardashev II, and immediately starts looking for Kardashev Is or earlier, and starts tossing rocks at them, just in case they don't go extinct in 10 million years, and somehow don't also become a Kardashev II in the next 10 million years, because as soon as they do, they're going to hit you with a rock in 20 million years? To put that in perspective, 20 million years ago was when apes and monkeys split on the evolutionary tree. 10 million years ago was when humans and apes split. At this point, you might as well toss a rock at every planet that has a biosignature, because 10 million years is a long time. Better keep tossing rocks in that direction, in case something else evolves. Maybe you better toss a planet at it, just be sure. That's only 2.19 * 10^37 joules, or 200 years of the sun's output. Shit. You better be Kardashev III. Wait! We know there aren't any Kardashev IIIs in the observable universe! Double shit!

If this casually genocidal Kardashev II civilization exists on the far side of the Milky Way, and wanted kill humanity, they'd be looking at homo erectus. They'd have wait another 100,000 years just to get a radio signal, and then what? Throw the rock immediately, and hope that in the ensuing 10 million years humanity hasn't learned how to redirect a relativistic rock? Or maybe they just threw the rock without even waiting for the radio signal, and it's on its way right now! Maybe the asteroid that hit 65 million years ago was a warning shot! Maybe they were trying to kill off a potential Silurian civilization before it even got really started, and ironically spawned us!

This strains credulity.

Replicator machines could outlive their creators. Then maybe most civilizations think it's safer not to risk being discovered by one, just in case it exists. That seems reasonable and doable.

You’ve gone from accusing me of a straw man argument, to postulating that not only do the Stargate Replicators exist, but every other advanced civilization knows they exist but somehow hide from them, even though by all conservative estimates, if Von Neuman probes did in fact exist, more than enough time has elapsed that the entire galaxy should have been converted to a grey goo by now.

Replicator machines “seem doable”?!?

Explain. Seriously. Explain what technologies and energy sources would create a complex autonomous machines from unrefined raw materials.

If it’s easier, explain how you’d make make a paper clip from first principles in the middle of a Greenland glacier. What are you going to do? Use electrolysis to split the water, and then have a fusion device fuse hydrogen into iron? Scrape across the surface to find trace atoms, and hope you find enough iron? Even if you have the iron, are you going smelt it, or what? How do you plan to forge it into steel, and then shape it? Are you going to use a tunneling electron microscope to place individual atoms? What’s the energy budget for this? How are you collecting and storing it? What’s the mass of this machine?

At this point, we’re talking about a World Devastator from Star Wars: Dark Empire.

“Seems doable”! Pshaw! EVERY ONE of these thought experiments from the 1940s are just magical premise to base a much simpler analysis on. In the case of Von Neuman proves, it’s determining a limit on how fast you could settle the galaxy. It’s not a serious technical proposal. It never was.

Still a strawman because I didn't say sci fi replicators. You could make an automated system that travels, mines, and manufactures. Like a 3D printer that prints copies of itself. That's not unbelievable.

You literally described sci-fi replicators.

I thought those were all-in-one nanobot things?

Nanobots are even dumber. They're magic.

The problem with von Neumann probes isn't the proverbial 3d printer. It's the filament. You have to build an entire supply chain for every individual component from first principles. That's why I asked how do you even make a single paper clip in Greenland. That's literally just a stainless steel wire. That's trivial compared to making an excavator, let alone an interstellar spacecraft.

Think about it. Mineral deposits aren't uniformly distributed. You're going to need to combine elements from thousands of kilometers away, and that's assuming their reachable from the surface with relative ease.

The only plausible way to build a "replicator" is actually to send entire premade factories, harvesters, and transports to a planet in a giant cooperative swarm, along with literally tons of preprocessed materials for repairs until you get a self sustaining supply chain running. And that implicitly assumes that all the requisite materials are even available. Land on a planet without plate tectonics, and your heavier elements may forever be locked under tens of kilometers of solid rock, or even better 60 kilometers of solid ice, liquid water, and rock. (Good luck with your Europan gold mine!)

Oh yeah, and it all of it has to work after a million years in hibernation.

So there's no benefit to collaborating because of distances and time scales. A system of machines is plausible, so there's a non-zero risk of encountering something like that. Civilizations decide to hide because only bad things could happen if they don't. And now you have a dark forest. The hunter doesn't have to exist. The prey just has to be fearful.

>plan that requires at this point quadrillions of individuals to be dedicated to multiple 100,000 year plans

I viewed it as more like developed nations funding WHO to erdicate outbreaks in developing back waters. Dedicating fraction of a civilization's resources to genocide viruses that no one wants to think about. Also at some point it's just another jobs program for a sufficiently large civilizational bureaucracy finding things to do and threats to mitigate for KPIs on their powerpoints.

You still haven't gotten around the 100,000 year issue. It's the energy expenditure and timescales that are the problem.

Even Star Trek's Q, doesn't care want to wait 100,000 years, and he's immortal, all powerful, and exists outside of space and time.

>energy expenditure and timescales that are the problem

Feels like that's anthropomorphizing human motivations (which Q at at some level was written to embody). IMO even for humans, not really an issue, wealthy countries spends fraction of discretionary budget to entertain long term projects. Last month Switzerland just commited 20B/3% of GDP on nuclear waste storage. Frankly, it could just be passing hobby of the nephew of some K1-2 civ energy sheikh sending out off the shelf grey goo genocide drones from his local cosmic mart for clout. Space twitch chat asked him to do it, and they do because it's a nonchalant activity, they're not thinking 1 minutes into the future let alone 100,000 years. They're not spending entire cycles of local sol energy to shoot expensive relativistic kill vehicles. They're spending pocket credits for a laugh, and 100,000 years later trillions of organisms end up dying. I think part of charm is recognizing the potential for lonewolf /small group of actors to be more dangerous than ever as societies move up tech tree.

I’ve already done the math about how hard it is to chuck a relativistic rock. Assuming solar output, you could arguably maybe do it as a Kardashev I, but it’s more a Kadashev II thing. It gets harder if you find yourself born around a common red dwarf.

If Zaphod Beeblebrox is chucking asteroids for lolz, while he waits for Slartibartfast to finish building a new pleasure planet (with space blackjack, and three boobed Martian hookers from Total Recall no doubt), we’re dealing with residents of Mount Olympus, with Zaphod playing the role of Zeus.

Come to think of it. That would certainly make the ancient alien conspiracies more entertaining —- and more terrifying.

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