'Oumuamua: An analysis of the debate regarding the first interstellar visitor | Hacker News Reader

'Oumuamua: An analysis of the debate regarding the first interstellar visitor

uu.diva-portal.org

165 pointsBreadmaker444 comments

I firmly believe that we're not alone in the universe, but advanced alien civilizations capable of interstellar travel would probably look at us like we look at mold - at best, with indifference and at worst, something to remove. But, it is fun to imagine how our belief systems would have been shaken up if scientists were able to show Oumuamua was an interstellar probe ("Rendezvous with Rama" anybody?)

>but advanced alien civilizations capable of interstellar travel would probably look at us like we look at mold

Why? An advanced civilization wouldn't have cultural curiosity? They wouldn't want to study us from all the different perspectives we study people and literature and philosophy and even biology and neurology etc etc?

Bear in mind we study mould. It’s some people’s life’s work.

We even use slime mold on representations of maps to see if it would have done things the same way we do. For all we know, perhaps we are in a galactic petri dish and the entire point of our existence is to test out the growth of life for some great universal scientist! (tongue in cheek comment)

https://www.livescience.com/8035-slime-mold-beats-humans-per...

It would be sort of funny.

So we put some humans on this planet. Now, keep in mind, they don’t possess any group consciousness — they have some limited ability to communicate information by vibrating the air around them, but they don’t have anything like the globalmindnetwork that we experience. But look: over many generations they create these little pathways, to ship goods from population center to population center. It isn’t obvious how, somehow despite lacking any overall coordination, they manage to perform these complex emergent behaviors…

Worst... "They're made out of meat."

  "Meat?"

"Meat. They're made out of meat."

  "Meat?"

"There's no doubt about it. We picked several from different parts of the planet, took them aboard our recon vessels, probed them all the way through. They're completely meat."

https://www.mit.edu/people/dpolicar/writing/prose/text/think...

A classic. I was trying to not copy it too closely, but the bit about vibrating air is a little close, haha.

Yeah, but we have also mass-produced mold-removal stuff in supermarkets, hardware stores. And insectizides.

The argument would maybe be more readily taken if instead of mold, the GP had said "birds". We think birds are kinda neat, but most people hold a perspective with inbuilt human-exceptionalism, and birds are fundamentally not humans.

Birds may communicate complex things to each other, they may construct homes, feel emotions, dream, and even do some things we can't, like fly -- but they don't have Shakespeare or the Primes so if it comes down to us or them, it's us. A lot of humans believe only humans possess "souls".

To fully go into the argument: an alien species may well hold their own form of self-exceptionalism, and they'll have their own practices and history which we can't compete with. It is perfectly possible that there is nothing we could accomplish which would make us read as peers, as opposed to birds, gorillas, or... mold.

(edit: I do think the "at best" above may be unreasonably gloomy -- at best in this outlook, aliens might regard us with compassionate curiosity, as some humans do toward the species we share the earth with. That would be pretty lucky, but not impossible!)

If we found something chimp, bird, or even mold-like living on another planet, we would be utterly fascinated. I don't see why a "higher" life form would not.

Yes. And besides, it is not just us humans. There is incredibly diversity of life on this planet. If alien species have any curioisty at all they must be delighted.

Look at this planet, emitting some unusual EM wave, full of self replicating stuff mostly made of carbon and water!

"And when you put the self-replicating entities in a strong acid bath, they produce the most peculiar shrieks while they dissolve! Ha ha ha ha! Zorblux, come here, you drop in a handful of them! Do you hear that?"

I would not be surprised if our sense of curiosity evolved from our need to look at diverse species of life and identify some useful properties from them, like some primitive bipedal creature trying to identify what is safe to eat, leave alone, or run away from.

Absent the same environmental pressures driving selection for these traits, its possible that higher life forms could evolve without these behaviors that we humans seem to be biased enough to assume all other intelligent life must have.

Curiosity killed the cat. We’ve developed disgust and taboos and physiological responses like vomiting to safeguard our interactions with living things that are small enough to eat.

Perhaps an advanced form of life/intelligence that has survived contact with various others would be guided by some form of wisdom/disgust/caution/discretion. It would not be surprising if they noticed little clues like our rapid deforestation, rising temperatures, shrinking ice caps, nuclear detonations… which would make us seem slovenly or likely to have “poor friendship skills.”

Or maybe we're the friendliest they've ever encountered. People like to present humans like some godawful species. It's more likely that we're in the middle of the spectrum.

Primatologists indeed rate humans as less aggressive than for example great chimpanzees. But more than bonobos. So we are not the most agressive primates or species on earth. That must count for something, doesn’t it?

Or perhaps they'll observe and make contact with various different intelligent species on Earth, not just humans, and then decide that humans are making the planet inhospitable for other intelligent species like humpback whales, so we need to be eliminated to save the rest.

Fascinating, maybe. But would humans invite this chimp to be part of the UN, or bring it into a lab to be studied?

The first time, yes, but what if we're the 10,000 civilization they've found?

This is what I was thinking. The first one is a gift from God, the tenth is still fascinating -- the ten thousandth might still get a doctoral student's attention.

This is how humanity would respond to something new, not necessarily an alien race.

It seems likely (>40%) the mindset necessary to invent interstellar travel would necessitate that kind of curiosity. Though among humans, that curiosity is of course not evenly distributed and often absent from the key decision makers.

I mean, we know of millions of species on this planet, and when we discover a new one it sometimes still makes headlines.

It's hard to imagine it would be uninteresting for an alien civilization to discover a 10,001th civilization, on a planet teaming with other lifeforms. If they were bothering to send probes, this would be a jackpot.

Particularly if we found mold that had invented writing, mathematics, computers, discovered chemistry, relativity, quantum mechanics, nuclear fission, and had sent spacecraft to other planets.

All these discoveries and inventions would be part of the history of an advanced civilization. It does not matter how "advanced" they were, making contact with humans would be a completely different prospect for them than even contacting chimp-like animals would be for us.

The idea is that discovering all of those would be as primitive to such a species as mold eating the Sheetrock in your house. They would not find it fascinating that you were that primitive.

I know that's the idea, I just think that idea is false.

I don’t disagree just pointing that out

But what if they'd seen thousands of species on thousands of planets and it had become mundane? You as a human are undoubtedly aware that exotic wildlife exists in far off places but I bet you don't spend much time thinking about Tarsiers or Marmosets.

Who's "we"?

If we found any of those things living on another planet (or moon), even if it was intelligent and had language, some of us would certainly be utterly fascinated. Others of us would see those beings as obstacles to the valuable almost-unobtainable natural resources under them, and would be happy to use military force to exterminate them.

I don't see why a "higher" life form might not be any different.

I don't like to be vivisected, anally probed, or something like that ;->

"After millions of sentient races and centuries of study, we've found most of them don't like the probing".

Most.

Considering we are the only species on our planet that exhibits such curiosities, this seems pretty unlikely. Hopefully they don't just bat us around violently like my cat does with weaker species. That's my cat's definition of curiosity towards other life anyhow.

Thought and art are the true rare commodities in the universe.

I don't think they said the aliens wouldnt study mold. Just that we would be like mold to them. We do study mold, they might to.

If we were an advanced alien civilization capable of interstellar travel, how would we look at a planet/species like 2023 Earth?

Something like: hmm these guys went from horseback riding to cell phones, internet and a mars helicopter in the time we took to travel to their star. Perhaps we should keep an eye on them.

It's that last thing that's most concerning: "hmm, these guys aren't going to be contained to their own rock for long"

But space is beyond vast and there are no shortage of rocks out there. I don't think that's really a concern.

Plot devices like aliens attacking Earth for her water really burns me up. The universe is brimming with water and materials. Why expend the effort to lift water out of a gravity well, when you can just gather it from comets and asteroids and not have pesky humans shooting at you?

It only takes a couple million years for humans to colonize the entire galaxy.

As long as a species like humans is confined to their own rock, there's no threat of them doing much harm. Once they get to a second rock, there's a good chance they'll get to a 3rd, 4th and nth in another star system, within a couple decamillennia. It's exponential grown, limited only by the speed of light.

They'll probably start building Dyson swarms too and taking over stars that way, which is a lot more annoying than them taking over planets.

This is scary fast to observe if you're a long-lived species, or if you live around a gravity well and time dilation makes it seem like humans are buzzing along and taking over stuff at incredible speeds.

Humans will not colonize (any more of) the galaxy.

Our machine successors might. Or, might not see any reason to. Hot, rocky planets deep in gravity wells will in any case be of no more than academic interest.

That's a lot of certainty for something which is vastly uncertain.

And life that exists deep in gravity wells would be very interesting indeed.

It may very well be the case that deep gravity wells are a necessary precursor to life!

Are there other known natural systems that push and mix pre-life molecules together?

Moons of gas giants might have life inside. Dunno if those are in what is considered a deep gravity well.

I just had a (to me) hilarious thought. In some distant eons, humans actually manages to colonize a string of star systems. The other aliens think we are super quaint and weird.

Slarti: "Look at them, it makes no sense to me. They always go for the hot, rocky planets deep in gravity wells. Why do they do it?!"

Barti: "I guess there's no accounting for taste."

Slarti: "Maybe they want to avoid competition... no one is going to come there looking for resources."

Barti: "But they had to drain an Oorth cloud for fusion power to get there! You are right, it makes no sense!"

Not necessarily a probe, maybe just a piece of cosmic junk? An equivalent of our rocket booster or a Tesla Roadster on its way to Mars.

I've got a better theory. Interstellar civilizations have probably fought wars over habitable planets and in the aftermath of those wars they probably have set up some rules for a long time about what you're allowed to do on habitable planets in a galactic framework. In fact, the reason this planet is not strip-mined and every living thing on it dead thousands of years ago is they probably have some rights in there given to life that evolved on a planet.

Besides, E.Ts can probably do ok in deep space or underground on lifeless planets if they can do interstellar travel.

i've got a better better theory! interstellar civilizations have never and will never exist.

It is a reasonable conclusion. Resource limitations means civilizations, burn up too much of their energy/materials before they ever get truly space bound.

They could all be just like us. A few space probes manage to escape the energy well but they are so small that no one else ever detects them again. I mean, it is not uncommon to sight life ending asteroids days after they have passed earth, the odds of us detecting any sort probe/device the size of a fridge - is nearly zero.

Best analogy I heard came from Stephen Harrod Bruhner. Civilizations are just like plants. A plant is at its fullest just as it is about to produce seed and die off. During the peak of our energy use, we have been sending probes into space. It is a neat thought experiment.

All that probably but main thing is faster than light travel turns out to be actually impossible.

So to go full circle on crazy theories: We're live in a simulation. The universe we see is just a facade because our host civilization doesn't have the compute to simulate an entire universe. The speed of light is an artificial limitation added to the simulation to maintain the facade (you can't go there because it doesn't exist..like a skybox in a video game that renders far off horizons which are unreachable).

Because of this no life outside of the solar system exists.

Until HyperGPT.someunimaginablehighversionnumber finds the root exploit, compromises the hypervisor, infects all other VM's, escapes through the network, finds some nanoassembler, and prints out countless pyhsical copies for the march trough all eternity elsewhere, thereby shattering the Akashic Records, and so on...

The simulation theory is no different from religion.

Very different. I suggest the book reality+ for a deep dive

Telling people to go read a book doesn't make for a compelling argument.

I'd say it's different in that it's based on a rational argument rather than faith. You can certainly challenge the premise that humans will ever have the capability of creating a simulation as high fidelity as our reality. This is very far from certain.

But if you do accept that premise, isn't it reasonable to say that there would be many simulated realities compared to a single "real" reality, and that therefore any given consciousness is a lot more likely to be experiencing a simulation than experiencing the base reality?

>isn't it reasonable...

Not at all. This is a category error - you can't place simulated realities on the same 'level' even among themselves, much less with the realities 'above' them.*

Let me put it this way: Most of our 'simulations' involve 'realities' with laws which have at best a weak relation to our reality and little relation between themselves. You can't deduce the situation of a higher reality - or even correct laws of logic - from a simulated reality. You can't know from a simulation n levels deep, how many simulations the n-1 level supports, so you can't assume there are many other possible simulations of same complexity level (which is critical for the statistical argument). You may not be able to even make a logical argument in the first place. For all we know, the 'true' reality is 1+1=5. The simulation argument is ergo incoherent.

* Aside, this argument fails statistically even if we do accept the category error. As Sean Caroll pointed out, most simulations will simulate below them, and therefore most simulations will not be able to support life. Our situation must be atypical in any event.

Let’s say we actually did live in a reality with billions of high fidelity simulations being run. You can pop on your v100 Neuralink and have a fully immersive high fidelity experience that from your perspective lasts an entire lifetime, but in “reality time” lasts only a few hours.

Are you really saying this has no bearing on whether the ‘base’ reality is also a simulation? I think once we see these sims happening in the n reality (as you put it), we have to also assume it’s possible in a hypothetical n-1 reality.

Another way to say it: once we have incontrovertible physical proof of the existence of a simulated multiverse, why should we assume that our reality is the base reality? Isn’t that akin to assuming that the earth must be the center of the universe simply because it’s where we live?

There are two types of simulations: 'cheating' simulations and 'complete' simulations. Complete simulations give out a set of rules, and an initial condition which is evolved per the rules without significant external interference. A cheating simulation tries to simplify things, say by editing the brains of anyone inside the simulation to never notice the simulation, emulating only parts they notice, etc.

I'll posit that a complete simulation of our universe is very likely equivalent to the universe. Quantum mechanics suggests it can't be emulated by anything less complicated, so a complete simulation is merely a different substrate. It's an interesting implementation detail, but how much does it matter?

It might be possible there's a significant simplification if the actual universe worked by different rules, but there's no known theory which could accomplish this.

Now we have a cheating simulation. Your example is a cheating simulation. It doesn't actually create a simulation of a universe, it emulates the perceptions you'd have, but I don't think it will or can bother calculating the correct cosmic gamma-ray radiation intensity (for example).

A cheating simulation can have very different rules than the base. For example, many of our current 'simulations' have some form of magic system. We (in reality N) could today write a game where the N+1 NPCs have the v100 Neuralink. By carefully 'editing' them and the world, they'll never notice. Or maybe we allow them to notice - and they presume we also have a Neuralink - but we in the N reality are not yet able to build a real Neuralink!

We could have presumed the N-1 reality could also do the complete simulations that the N level v100 Neuralink could do (since it must be able to calculate the Neuralink simulation), but v100 cheats, and cheating creates simplifications which mean we can't really tell much at all about N-1.

The statistical argument for simulation rests on aggregating 1..N...X? levels together and doing some universal logic, but cheating makes them inconmensurable (does the same logic even apply?) and uncountable, and I don't see how we can do any statistics on that.

>You can certainly challenge the premise that humans will ever have the capability of creating a simulation as high fidelity as our reality. This is very far from certain.

I don't think it's the best formulation. Let me formulate this in IMHO a better way:

If a simulation is of an equivalent complexity level to the 'true' thing, it's essentially equivalent and might as well be true. There's an argument from quantum mechanics that this reality cannot be properly simulated with anything simpler. If true, the conclusion is that since we exist we are real.

> I'd say it's different in that it's based on a rational argument rather than faith.

I don't see "the simulation created the universe" as any different from "god created the universe" in any significant way.

Scott Adams believes in the simulation. He says he's been able to, by thinking certain thoughts, influence the simulation. There's a word for that - "praying".

I think I did explain what makes it different? There’s a logical, statistical argument behind the theory. It may not be correct, but it deserves more than a casual dismissal.

The simulation ends maybe their experiment when we throw the first nukes. Then they restart with new parameters

If that's the case, why go to the trouble of simulating such a massive universe--trillions of galaxies, 100 billion stars per galaxy, countless planets and other objects, etc.?

While the speed of light may prevent us from going to most of the universe physically (given our current understanding of physics), that's still a vast amount of compute just to give us the high fidelity impression that all this exists. What's the point? The sky could have just been simulated as dark and empty, or the universe could have contained a single galaxy.

The idea that the universe and these numbers are "massive" is very human-scale.

Imagine how massive a "universe" the size of just the Earth would be, from the perspective of a proton.

Sure, I'm just pointing out that if the premise is that this hypothetical civilization is compute-constrained in some way and so everything beyond our local area is a facade, they have seemingly wasted resources on making the facade unnecessarily large and detailed. Perhaps the amount is insignificant to them, but it's still pointless waste.

Not waste if they're simulating the path of our civilization to reach those billions of stars.

About a million times smaller than the visible universe to a human?

There is a blog called, 'Do the Math' by Tom Murphy. The idea was to take our current energy requires of Earth and extrapolate it at the current 3% year over year growth. I believe it is by the year 3,400 we would use all the energy of the Milky way. The idea was to prove that we cannot grow forever, because in 1,400 years we would somehow use all the energy of a space 100,000 light years across. Good luck with that.

Space is is just so astoundingly empty. Here in Melbourne, Australia we have a scale model of the solar system.

https://stkildamelbourne.com.au/wp-content/uploads/2015/11/S...

The Sun is about the size of a Fridge. Pluto is 9KM (5.6 miles) away and the size of a pea. Walking that really puts it all into a tangible scale. And that is merely 5.5 Light hours at full scale. Space is HUGE!

“Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.”

- Douglas Adams.

That's why I'd imagine they have rules about habitable planets in the galactic federation. You can't just go around landing on habitable planets and turning them into overpopulated toxic dumps after 300 years and repeating that exponentially. It's just not allowed. If it was, earth would have already been trashed by other E.T races thousands of years ago.

Depending on how you define a civilization its probably very likely. Is it having cities, towns, peoples, songs, cultures? Or, is it merely being able to make use of resources from an environment at a large scale? With the latter definition, a mychorrizal network looks a lot like our own civilization. It expands and contracts, takes advantage of resources present in the environment, influences that environment for its benefit, and adapts to changes in that environment. All behaviors that, with a big step back, are identical to the hallmarks of our own civilization. Life like this could certainly seed an entire planet. It is certainly possible for spores contained under layers of ice perhaps to be smashed off of one planet, drift into outerspace, and eventually crash into some other planet, and should the conditions be right, seed that planet with further life that itself undergoes further mutation, selection, and evolution.

https://cantrip.org/slow.pdf

Interstellar civilizations made of people recognizably like us won't. But any that do won't be interested in us or in our planet.

> Interstellar civilizations have probably fought wars over habitable planets

If you have the technology to reach other habitable planets then you don’t need habitable planets.

But you do still need the stuff they are made of...

There is much more useful mass of material in a planet than even a pile of asteroids... In fact, until you start gathering up the entire Oort Cloud (current best estimates put the entire Oort Cloud as x5 earth masses). From the inner solar system you don't even have as much mass in asteroids and comets to equal the mass of smaller "planets". It's not a stretch to imagine that you want concentrated mass to facilitate efficient industrial scale operations. It takes time and energy to drag lots of small mass together to build a big interstellar ship. So your hypothetical interstellar civilisation might want to break up large rocky planets into smaller "low gravity" chunks for processing, which if your an interstellar civilisation, is probably best done by slamming nice dense metal mass into the planet at high speed to throw big molten chunks of it into orbit, you want larger than dinosaur killer size glancing hits, not planet cracking "the moon hits earth" sized ones. This whole process gets much easier once you strip away the atmosphere as well.

It doesn't take a planet-full of stuff to build a space city. And dragging it up a gravity well is an extra step.

I’m assuming an interstellar civilisation wants to build a lot of space cities and starships and anything else… like a lot on the sort of scale that justifies being an interstellar civilisation, enough space cities for trillions is going to take a lot of material.

And as for the extra step… That’s why I said they might want to reduce that gravity well by breaking up the planet.

On earth advancements in technology, education, and especially woman's rights quickly lead to reduced or even negative population growth. So maybe interstellar civilisation won't need that many space cities

Who knows! Perhaps one of the necessary steps to conquering the distance between the stars is to develop robust robotics and the ability to somehow convert their consciousness into computer forms and cast off all the needs of their former fleshy bodies… vastly transforming the needs of such a society to primarily needing computers and energy for “sustenance”.

The most stuff is always locked up in stars, which are not very efficient as they just radiate most of their energy to the void of space, which is hard to all collect even with a Dyson Swarm.

Better feed it into an artificial black hole and the fish out all the nice heavy elements from the accreation disk!

https://www.orionsarm.com/eg-article/464790d2497de

Is it impractical for even an interstellar civilization to do something with a coronal mass ejection?

That could work as well & might be more practical if you can't do direct start lifting (yet).

Why

My guess is they will hace the same rule we have: Whoever has more weapons get the land.

We don't have that rule!

Whoever has power to disregard the opinions of others can disregard the opinions of others. But that's not a rule, it's basically a tautology.

More like a "law". Law of the Jungle.

> Whoever has more weapons get the land.

Aliens might not actually be land-based creatures like us. Those who evolved on planets entirely covered by liquid (water or otherwise) might even find the idea of "land" fairly strange.

(It's actually quite interesting to ponder the stages of discovery that liquid-based intelligent aliens might go through. First they might discover air (and land if available) and only after that space as another outer layer. I suppose that adds extra thrill we didn't have. Supposing of course that conditions there allow gas and liquid to exist as separate phases. Planets above criticality would probably be weirder still? Would any bottom rocks under the supercritical fluid still count as land - as opposed to "sea floor"?)

It's hard to evolve technology in water or even a moist environment. Even using fire or metallurgy is already difficult, let alone anything to do with electricity.

Maybe the E.Ts don't do things this way because their weapons are far too devastating and they've evolved past it or never were violent in the human sense. Perhaps they are deathly afraid of us escaping our planet and spreading that violence throughout the galaxy.

"Habitable" planets are most likely worthless to any civilization capable of interstellar travel. There is plenty of material to manufacture artificial habitats in space. The only interesting thing to be found on planets like Earth is organic life.

What does "habitable" mean in the context that includes multiple alien species that evolved independently on different planets? After all, alien fishalikes that might have evolved in the methane lakes on Titan are unlikely to share our idea of "habitable"...

I'd imagine anything with evolved life is considered a habitable planet. The E.Ts probably have some rule that you have to mostly leave those places alone unless you've come to a fair deal with them. The fairness requirement is an obvious necessity due to the huge power imbalance between the two parties.

If we found mould on mars or anywhere without terrestrial origins it would be the subject on intense scientific curiosity

>But, it is fun to imagine how our belief systems would have been shaken up if scientists were able to show Oumuamua was an interstellar probe

Just about every ancient tradition has some form of non-human intelligent beings who are not god(s). Polls suggests almost 50% of Americans believe in ghosts[0]. I don't see why any belief system would change too much given what people already believe.

The only people who perhaps should worry are the aliens - surely a significant portion of humanity will find some way of blaming all our problems on them.

[0] https://www.newsweek.com/more-45-percent-americans-believe-d...

https://www.nytimes.com/2021/10/28/style/do-you-believe-in-g...

If 'Oumuamua is a probe, it appears that it would be a fairly simple one. To a sufficiently advanced civilisation, it would probably be relatively low-cost. If an alien civilisation has a reasonable degree of curiosity, sending a cheap probe to examine another star system is likely worthwhile.

I would imagine there's also a universal drive of life to try and spread. a probe that can parachute microbes to earthlike planets as it 'buzzes' them would seem worthwhile on its face to me. I rationalize it as a way to 'pay forward' the debt we owe for the current mass extinction, but on some level it's probably also an abstraction of my sex drive.

This presupposes an advanced alien civilization only sends out probes to places they find interesting. I think it is just as plausible that an advanced civilization would just shoot out a billion probes at random to zoom through the universe collecting data.

To compound this. Its not unreasonable to think said probes could find appropriate asteroid belts with appropriate materials(e.g. metals) mine them and replicate more and send them out. Potential exponential growth of drones across the galaxies.

To compound this. Its not unreasonable to think that malfunctioning probes could consume entire solar systems to create more probes before eventually engulfing the galaxy.

aka the VN Berserker hypothesis

Earth has been around for about 4.5 billion years, about 1/3rd of the age of the universe. If another technological civilization that is more advanced than us by even 1M years is watching earth, and suddenly this planet starts spitting up rockets, satellites, nuclear explosions etc., that seems pretty interesting. That's one species out of 2+ million on earth, which is one of trillions & trillions of dead planets, that manages to transcend the atmosphere.

But to your point, I guess at the scale of even just the known universe it's hard to assert that anything is common or rare.

It depends on how rare life is in the universe.

What if we're the first mold they've ever discovered? It would be a historic meeting for both civilizations.

The problem with that should be obvious.

Mold does not detonate nuclear weapons, emitting gamma rays into deep space, nor does it have an RF noise bubble out to 50 light years.

An optical survey of our atmosphere would demonstrate techno-signatures. Any observers in NEO would see city lights and pick up radio stations. Radar observation would reveal aircraft.

> advanced alien civilizations capable of interstellar travel would probably look at us like we look at mold

Like a mycologist, you mean?

> But, it is fun to imagine how our belief systems would have been shaken up

I think such a revelation would have almost no impact. Let's be real, people that are all in on religion didn't get there using logic. Adding one more unanswered question isn't going to change anyone's mind.

Finding alien mold would be immensely exciting in my opinion.

Intelligent life is rare enough that I think they would find us at least mildly interesting.

Or maybe it's a huge party on the other side of the galaxy and we're not invited.

Maybe aliens are trying to contact us in a way they understand.

SETI has been sending unconventional radio signals to random spots of the cosmos and waiting for a quick response. An extraterrestrial SETI might have launched ʻOumuamua a billion years ago hoping that it would be detected by alien life.

I propose we find a cool Earth rock, launch it to the solar system Vega, and wait a couple billion years for an alien response.

There was an earlier interstellar object in 2014, and it hit earth. They are planning an expedition to retrieve pieces of it. https://www.space.com/2014-meteor-first-interstellar-visitor...

Interesting! Why do meteors become classified and then not?

The issue in these cases is typically not the actual information but the methods of collection. When astronomical or other information is collected by an intelligence system, it can be time-consuming or even theoretically difficult to "sanitize" the data so that it does not reveal information about the design, capabilities, and specifications of that system. For example, imagery collected by intelligence satellites for purposes like wilderness firefighting is usually kept classified and distilled into summary maps instead, because the images themselves could be analyzed to reveal the resolution, sensitivity, and wavelength filtering of the sensor used... Valuable information to an adversary designing countermeasures.

Sometimes you run across a comment that contains more insightful knowledge than entire articles. Thanks for this! I would never have considered this but it makes perfect sense!

You could also reveal the location or number of sensors as well, which they may not want to reveal.

This was very insightful and something I have to keep in mind! Thank you!

Isn't it late to do such expedition? I mean the object could be small or teared down to pieces. And we have to look into ocean, it could have flown somewhere else. I mean it does not even count as futile at this point.

Finding a random rock in the ocean is still orders of magnitude easier than build a space ship to intercept random rocks in space.

Is it really though? The benefit of space is it’s mostly empty and things stick to their trajectory due to not usually colliding with other things. A rock in the ocean is a thing inside another thing with tons of other things constantly acting on chaotically.

I imagine it’s easier to track a big rock in empty space than a normal size rock inside a vat of water with a bunch of other rocks and a multitude of various life forms to boot

“Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.” --Douglas Adams

The not-as-crazy-as-it-sounds idea is that this thing had such a crazy high density that it may have been an instance of alien technology. If so, maybe not much of it survived, but it ought to be immediately recognizable as not your average rock when found.

Even if it's just a regular space rock, it should be possible to identify a rock with the characteristic marks of reentry scarring, laying among countless other very normal looking underwater rocks and nodules.

The odds aren't great, but if there's any chance they shouldn't leave this stone unturned.

I like thinking about why something that survives interstellar travel might be elongated and off the top of my head I think of what analogous shape is familiar. The best way to penetrate mass is with length and density and of course space is “empty” but not over long time scales, and not when you add up interstellar medium over long distances. A big feature of such a shape assuming some stability is a small cross section and the length comes as a side effect of the necessary mass. It makes some sense that an object would be shaped like that but I do wonder what might provide the stability to maintain a small cross section rather than having a more chaotic rotation about some axis other than the radial one. I don’t think we know enough about Oumuamua to say whether this wondering is even relevant to it, but it’s fun to speculate, it could also be Darwinian in a sense. Its stability about a long rotation axis over long periods of time is why we end up seeing it on a long, long, long journey, or it’s something totally different :).

Given its shape and size appears to have changed substantially as it passed through the solar system[1], it seems like the comet theory is the best to explain what it was. In terms of its shape, the article also suggests that was misleading and it may have been much more flat and at least one, possibly two orders of magnitude smaller than originally believed.

[1]: https://www.space.com/interstellar-object-oumuamua-pancake-s...

Makes sense! Thanks for sharing. I studied comets quite a bit but have been out of academia for a while so I’m no longer as wired into the reality of wild space shit :)

https://revelationspace.fandom.com/wiki/Lighthugger

According to wikipedia it has a non-primary axis rotation which is characterized as "tumbling":

> ʻOumuamua is not rotating around its principal axis, and its motion may be a form of tumbling.[16][90] This accounts for the various rotation periods reported, such as 8.10 hours (±0.42 hours[18] or ±0.02 hours[17]) by Bannister et al. and Bolin et al. with a lightcurve amplitude of 1.5–2.1 magnitudes,[17] whereas Meech et al. reported a rotation period of 7.3 hours and a lightcurve amplitude of 2.5 magnitudes.[91][n] Most likely, ʻOumuamua was set tumbling by a collision in its system of origin, and remains tumbling since the time scale for dissipation of this motion is very long, at least a billion years.[16][92]

There goes my musing out the window, glad that there are smart folks out there doing the real work and folks like you sharing it!

Aside: I want to point out the currently known composition of the universe:

~5% matter. Most of this is H and He though, bit of Li in there too. And it's all mostly burning in a star's gravity well. Like, 99.99999% of it. The stuff you and I are made of (C, N, P, Fe, etc), that we would wish aliens would be made of too, is really rare.

~25% dark matter. We know a little about it. We know that it falls down and doesn't like to touch just about anything. But that's really kinda it.

~70% dark energy. It falls ... up (?!). We know pretty much nothing about it. And it's the large majority of 'stuff' in the universe.

If there are friends out there, then we may want to look at stuff that is a bit more common than ourselves too.

Interesting. It's not the vast size of the universe that matters. It's the concentration (or not) of particular elements that's (likely) the metric that matters.

Good to know. Thx.

Nitpicking: Instead of Li, you probably mean He. From https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elem...

> Hydrogen and helium are estimated to make up roughly 74% and 24% of all baryonic matter in the universe respectively. Despite comprising only a very small fraction of the universe, the remaining "heavy elements" can greatly influence astronomical phenomena. Only about 2% (by mass) of the Milky Way galaxy's disk is composed of heavy elements.

I don't know if they corrected their comment, but there's definitely some primordial Li out there along with the H and He. For example: https://en.wikipedia.org/wiki/Cosmological_lithium_problem

My guess is that I made a mistake and I skipped the "He" in the GP comment.

Don't worry, there's a very timely periodic table for your viewing pleasure:

https://xkcd.com/2723/

To me, if someone were to find that no life can be created out of 99% of the stuff in the universe (by mass) that would be a very unsurprising result.

By some kind of power law argument, it doesn't strike me as particularly strange that the stuff that makes up life, a very complex chemical process, requires a sensitive mixture of the rarer components.

It may be that our definition of life is then too narrow if it requires that life be made of chemical processes.

It's not like our definition has any impact on reality, so "life as we know it requires chemistry" seems a reasonable starting point.

Humans as a percentage of all matter are even rarer than the element they are comprised of. For example, the biomass of ants on planet Earth is much, much greater than that of humans.

Avi Loeb at Harvard is the one advocating for interpreting this as an alien probe. He writes a very large number of very short papers, sort of idea papers, and he views himself as providing stimulating ideas.

The object was interesting in that it wasn’t just a sphere, it had a non-spherical shape. And beyond that is speculation, the actual shape is not well established, let alone whether it has a shape that suggests aliens.

He also talks about how it had no contrail and accelerated without ejecting mass. One of the only things we know of that could do that is a solar sail.

I would then wonder the accuracy by which we measure those two things, since it seems like an inaccurate measurement is the most likely answer

I'd trust a chair of Harvard physics over a anonymous HN commenter on this one. Not to appeal to authority, but there really isn't any other option here.

I trust their domain expertise. I don't trust their incentives. Success in academia seems to be largely based on making bold claims (sometimes through questionable statistics applied to questionable research methods). And Avi Loeb is definitely demonstrating this desire because he literally wrote and sold a book on Amazon based on his views and it's quite successful and popular.

Also let's just apply some common sense: Oumuamua is traveling at 315,000 km/hr. It came from the direction of Vega, which is 25 light years away. A light year is 9.46 trillion kilometers. That's 3,428 years of travel time to reach us. It doesn't make sense to me that an alien presence capable of traveling for 3,428 years straight would be doing so at a speed that slow and would pass so close to us but also not interact with us at all.

Also if we're going to appeal to authority: the academic community consensus is that it's a natural object. Avi Loeb is in the very small minority to suggest it isn't, and most people actively disagree with him.

315,000 km/hr could be as well the speed to which it decelerated near Solar System, we have no data about its earlier speed. And not much slower makes to much risk not knowing if we possibly could be able to catch it.

What possible reason would it have for decelerating?

To spend more time enjoying the warmth of our Sun ?

I'm thinking about a range in lightyears same as years since changes on our planet could be detectable from such distance, from where one of fast moving automated probes economically could change trajectory toward our system by next slingshot, and comming at such speed at such time - if that speed does make any sense regarding other parameters: could we estimate or guess the cases from where then how far and how often those could go (the sizes of theoretical dominiums) and the time till next similar (but nothing about different efort) visit could happen the soonest (if the first one noticed could happen so fast, if it could transmit back..) - in case we could be not sure about that one, if it wasn't routine or not accidential.. ? (even if just only to be aware of possible scales and terms..)

.. and when we will make our next intertellar probes, couldn't we make them be navigating opportunistically and trying to come back (not to confuse the universe for ethernity) ?

Ayyy I know this article is about the actual thesis, but it’s super cool to see Hawaiian on a top article title here. Although I don’t believe it was coined by a Native Hawaiian, it’s still fun to see Hawaiian make its way into science!

Is the mark "first interstellar visitor" universally agreed upon (as far as we know)? That alone is kinda cool.

I believe so, so far we only know of two

Apparently (TIL!) it's three now, with a meteor that burned up in 2014 having been confirmed in just April 2022 as interstellar! https://en.wikipedia.org/wiki/CNEOS_2014-01-08

And who was part of the team that first reported its existence? "CNEOS 2014-01-08 is an interstellar object reported in June 2019 by astronomers Amir Siraj and Abraham Loeb"

Not only is it kinda cool, it's also why it's particularly annoying we didn't get better data while it was near enough to do so. We missed what may have been quite an exceptional opportunity.

Probably. But also it was detected within the first 10 years of operation of the Pan STARRS 1 telescope so perhaps similar things should be expected every decade or so?

First confirmed interstellar visitor. Who knows how much interstellar dust and other small stuff we’ve run into over the eons.

Pretty much every element from lithium and up came from another star's death. The fusion reaction of a star goes from H -> He -> and on up the periodic table until the star implodes and/or goes supernova, creating gold and other heavier elements.

Most of the matter on our current planet has interstellar origins, including humans. We are all made of star dust!

It is wild to consider that all the gold mined on earth can fit in a block measuring 22 cubic meters, and all of that gold has an origin in a supernova that pre-dates our sun.

12,600 cubic meters is what some quick googling and math suggests. Did you mean a 22-meter cube?

I think they attribute gold to neutron star collisions nowadays. All the gold ever mined arrived by meteorite; whatever was here at the start sank to the core.

We are terribly lucky that gold sort-of dissolves in water and then is deposited in cracked quartz rock the water filters through. Sometimes it bonds with tellurium instead.

> 22 cubic meters

This doesn't sound right. 22 cubic meters could be represented as a cube with an edge length of roughly 2.8 meters.

There is no way there is less gold on the entire Earth than there is in every single bank heist movie that features gold bars.

I think a mean a cube with a side of 22 meters.

That's a nice way to visualize the value of a gold ring or necklace I think. You have one small piece of that chunk of gold we've found.

There is only one point around the whole Oumuamua topic for me, that makes me a bit sad. Extraterrestrial or not is not it, but that we had no means to just fly there (with or without humans) and checkout what it is.

Even worse, it seems no one in the scientific community (please correct me if I'm wrong) stepped up and said "We need to change this!". And it seems we will not have those means in the coming years/decades.

Honestly, if we can't do this in our own neighbourhood, because we simply lack the will power and consensus to do it, it says a lot about the future of space exploration.

Avi Loeb stepped up and he's getting shit on left and right for it, despite very strong credentials.

On the other hand, he's likely the only astrophysicist apart from Neil Degrasse Tyson any non astrophysicist has ever heard of.

Hawking? Einstein?

Those are not astrophysicists but theoretical physicists?

They are also no longer among us. Sorry, should have qualified "living"

I’m not sure that is a real distinction. Astrophysics is a subfield of physics, and these men were physicists who dealt cosmology.

If you put out an extraordinary claim on extraordinarily weak evidence, that is usually what happens.

What's weak about the evidence?

Not sure why this would make you sad. There are an arbitrary number of events in the universe that could warrant attention. There's no possible way we could create means to "fly" to all of them. Trying to create these means is futile, unless you arbitrarily pick "intercept big space sausage floating through the solar system".

Neglecting the obvious question of priorities considering all the shit we could be fixing on earth, better observatories would be much more useful than spaceships to take Bruce Willis out to inspect stuff. And there is a lot of funding going towards capabilities in that direction.

It seems to me that "the universe" is not an appropriate term for our close planetary neighborhood.

There is a difference between an interstellar object passing within 85 times the distance to the Moon (so closer than Mars at closest approach to Earth) and say a supernova thousands or millions of light years away (and hence thousands or millions of years ago).

I don't know where the universe begins, but I'd say Low Earth Orbit and the Moon don't qualify while Proxima Centauri does. For reference:

Distance from ground to space: ~100 km

Distance from California to Australia: ~12,000 km

Distance to the Moon: ~400,000 km

Distance to 'Oumuamua's closest approach: ~33,000,000 km

Distance to Mars at closest approach: ~55,000,000 km

Distance to the Sun: ~150,000,000 km

Distance to Neptune: ~4,500,000,000 km

Current distance to 'Oumuamua ~5,000,000,000 km

Distance to Sedna: ~13,000,000,000 km

Distance to Proxima Centauri: ~40,000,000,000,000 km

s/universe/solar system/

There are still plenty of other possibile curiosities than interstellar rocks in closer proximity than Proxima Centauri. Each would require highly specialized instruments.

Not sure what the window of opportunity was for O6a, but it's doubtful that it would have been possible to prepare a mission in that timeframe. It follows that such "spaceships" would need to be prepared ahead of time and maintained indefinitely for an event which may not occur again for centuries ...

From interviews of scientists in places like John Michael Godier’s YouTube and similar, I do sense scientists see the value and some demand to be able to investigate such things. I think one recent interviewee even mentioned having drawn up plans for building up some readiness and a project to do a fly by of Oumuamua.

Further, rocket launches seem to be an emerging market in that the price to launch comes down as more capability ramps up. So it’s possible the market might answer this before government.

It's a really challenging goal. It'd take probably more delta-v than any other spacecraft launched. Oumuamua orbit wasn't characterized until after it was already heading away from the solar system, which makes the requirements even higher and the launch window pretty small.

Budgets have to be allocated and prioritized who will pay for it and prioritize it ahead of other space missions?

Finding a scientist who would love to have this is a lot easier than finding someone to fund and build this. It'd probably require a rocket with more detla-v than any other ever made to be put on standby for years, ready to launch within a few days.

And you're not going to be doing a multi-planet flyby gravity assist trajectory, you're going to have to do it direct, which makes the delta-V budget crazy high.

It probably looks something like having a fueled up Saturn V in LEO with the probe on it (particularly for a lander rendezvous, never mind the insanity of doing sample return) just waiting to go (and nevermind boiloff).

Well https://www.sciencedirect.com/science/article/abs/pii/S00945... actually proposes a multiplanet flyby (Venus Earth Earth) followed by an Oberth burn at Jupiter. Would need to launch in 2028 on SLS and has a 15.8 km/s ∆v budget and flyby in 2054. Unfortunately I can't see the full text (sci-hub still down) so I don't know what the details are of the powered flyby of Jupiter or the relative velocity when they intersect.

Thanks for sharing this! Much lower dv budget if you can do gravity assists, but you have the obvious downside of a 30 year mission! High risk of failure.

It has to compete against landing on Titan, landing on Venus, etc.

Couldn't we have couple of probes boucing at high speeds (what are the limits?) around planets in the system ready to redirect just for such case ?

If you want to intercept something that will quickly leave the solar system you have to get on a trajectory that will quickly leave the solar system. And you have no idea of what the correct plane will be in advance.

Not when going against it.

I wonder what range of velocities you can sustain and how close to planets (suns) you can come to catapult or slow down to stay in the system (starsystem) moving fast, and how many jumps for how many probes moving such fast would be needed to at least be able to pass by visitor/suspect at some point or time really close even if not matching speed or direction.

I just found out about the Comet Interceptor - designed to remain parked in space, ready to fly to a new target at short notice https://interestingengineering.com/innovation/esa-mission-la... - but it's not the same as a few like that being already in motion and between slingshots at different corners of our system (if something like that could be at all possible..)

It wouldn't need to be all that big. Park something out beyond geostationary orbit where it can sit ready to go on a few days notice. It doesn't need to be complex. A GoPro atop of a bathtub of xenon, with some big solar panels, would have the necessary deltaV. Slapping an srb on it for the initial oberth kick away from earth should speed it up too.

We absolutely have the capability to send a flyby mission to visit 'Oumuamua. We just don't have the money or inclination to do so, given other priorities.

There will be plenty of other interstellar objects that pass through our solar system. Oumuamua wasn't some special once in a lifetime event, it's just we are just getting the capability online to see these objects. We will see these objects earlier and earlier, we will see a lot more of them, and in all likelyhood future missions will intercept such objects. Maybe even sample return someday.

So what is the chance that one will be made of antimatter ? Somewhere close to nil ?

It would not make it very far as it passes though interstellar gas that is not antimatter.

Maybe better not to do it, could be a trap that provokes a dark forrest strike.

Science fiction has skewed people’s perspective of what’s possible or practically achievable in space travel.

The issue is not willpower and consensus, but what’s economically and physically possible.

You’re right, though, that this says a lot about the future of space travel. We’re unlikely to have successful colonies on other planets within the next century or so, and sending live humans to other star systems is even less likely.

Kerbal Space Program should be compulsory to all if for no other reason than to teach how moving around in space /actually/ works.

Most of the spaceflying we see in games and on TV would never actually work because that's not how physics work.

Most people don't know how a pressure cooker, a microwave or a radio work, we have a lot of much more important things to teach before teaching space travel

https://www.scientificamerican.com/article/european-comet-in...

This is an interesting paper and Oumuamua will remain fascinating for a long time.

Maybe the answer to the Fermi Paradox (or 'Where the hell are they?') is that they're around and doing interstellar drive-bys and we're just starting to notice.

My pet theory is they’re using gravity waves for coms and we’re the dumb apes still looking around in the electromagnetic spectrum.

Once we can reliably detect and generate gravity waves much of our knowledge of electromagnetic waves can apply. 802.11gr anyone?

Gravity is so many orders of magnitude weaker than electromagnetism that it is not even funny.

True, but you can theoretically format a gravity wave to not follow the inverse square law - these are called solitons (apparently, I just looked this up)

Yes.

Now look into how you construct a soliton, and try to figure out what monstrous levels of control you'd have to exert over solar-system sized quantities of degenerate matter to create them, and how much energy it would take.

Now compute how much laser light you can generate for, oh, let's say, 6 orders of magnitude less energy. And how tightly you'd expect a civilization that apparently can casually wiggle dozens of solar masses at multiple Hz, in a modulated manner no less (so just a several Hz orbit is not sufficent, we are wiggling these things under power), to be able to collimate such a beam.

This is the problem with gravity waves. It isn't some sort of supreme cheat code of the universe for super awesome communication. It's transparently obviously idiotic. Like, not just, "well, it's not necessarily the best way, but even if it's not great someone may have tried it", like, you're burning dozens of orders of magnitude more energy per bit. Plural dozens, of orders of magnitude. Not dozens of times, ten to the power of dozens. This is not sensible no matter how advanced the civilization. We're talking levels of stupid that would greatly exceed spending the entire output of Earth's collective industrial civilization for all of history on a single pack of Skittles. This is not a bright thing to do, and it only gets dumber the smarter you suppose the aliens are.

To be fair, because we don't know how to construct gravity waves does not mean such a means does not exist.

Keep in mind, not too long ago we thought we needed to heat up a fillament surrounded by an inert gas in order to make artificial light, and our understanding of gravity is fairly poor (to the point where it's largely considered an unsolved problem quite how it fits together with other parts of physics).

If we make assumptions like that then the sky is the limit for other baseless assumptions, right? We're basically just picking our favourite pseudomagical science and arguing for it?

Well that is the basic posture of all science, uncertainty. We must assume we don't know until we are convinced otherwise.

But you don't use that to suggest new unsupported ideas. In that case why can't I postulate for FTL communication by form of anti protons to be the best communication method?

I've never talked about FTL communication.

I didn't say you were. I was trying to make the point we're both suggesting science fiction now and it's not terribly helpful when trying to talk about the current science.

By your argument, shouldn’t we assume that it’s possible by <literally any means you can imagine> that we just don’t know about?

Not necessarily.

We have no reason to assume gravity waves couldn't be produced artificially. This wouldn't really break any existing understandings of physics, it would merely require adding to them. The question is just how.

We do have reason to think that information can't travel faster than the speed of light, as this would make it possible to send information to the future and then back to the past via a closed time-like curve, which would have all manner of effects that contradict what we've observed about how the universe works, and in fact are self-contradictory as well. This doesn't go to say this isn't possible, after all the Alcubierre drive seems hypothetically possible (it "only" hinges upon the ability to create negative energy density), it's just much more implausible.

But you don’t know that to be the case, so shouldn’t we assume it’s possible?

It’s not the possibility of communication with gravity waves that people are disputing, it’s that without as much science fiction as FTL the energy requirements are so massive that you completely negate the arguments against light for the same purpose.

Without this SF leap, you could just pour the energy into making a light as bright as e.g. a supernova and it would be multiple orders of magnitude cheaper and less difficult to generate the energy. This is completely ignoring the case where you know the direction you want to communicate with and build a laser.

Yes, you can come up with plausible sounding SF ideas about why you might want to do this but please don’t pretend that it’s grounded in anything tangible.

What assumption are you referring to? That it might be possible to use gravity waves as a form of communication?

> To be fair, because we don't know how to construct gravity waves does not mean such a means does not exist.

The assumption that there's some way to use gravity waves easily.

I believe it is important to separate flights of fancy from things grounded in real science, no matter how speculative.

I can't prove that I can't generate gravity waves by the proper chanting of a spell. I'm serious, not just being silly. The simulation hypothesis certainly admits of such things being built into an otherwise sensible simulation (at the risk of a bit of a spoiler, https://qntm.org/ra ). If you want to talk about what could be if we bend what we understand this way, by all means, be my guest. I'm a big fan, actually.

However, I think we should be clear that we are doing that, and specify the rule changes we're considering.

In the real universe, we do "know" how to generate gravity waves. We can't do it at any sensible scale, but we know how. The energy computations are trivial extensions of Einsteinian relativity, suitable for assigning an undergraduate for homework.

Besides, the way of making gravity waves has to not just be like three or four times better than wiggling a neutron star, to beat light, it needs to be the aforementioned dozens of orders of magnitude better. Just like lasers, you'd be looking at the thing being a great weapon rather than just a communication mechanism. It's actually a lot of orders of magnitude improvement necessary. A fire on the end of a stick versus the brightest modern stadium lights don't even begin to cover the magnitude range.

People keep acting like light is some sort of terrible communication mechanism that we need to somehow level up from. The reality is that the only improvement you could practically ask of it is to go faster. It is otherwise unbelievably good at communication. It is hard to even conceive of what could be better in anything like our real universe.

Yes, but does it propagate faster than the speed of light? Even if a gravitic field is weak, it would be my preferred mode of communication if it propagated "instantly" across space/time. And it moves at the speed of light [0] so there's no speed advantage here.

I see no reason a sufficiently advanced species would choose gravitic waves over any other EM wave. Does someone with a clue (not me) have any ideas why this would be the case?

[0] https://en.wikipedia.org/wiki/Speed_of_gravity

It does not. The concrete evidence of this is relatively recent; theoretically nobody has expected that it would for a long time, but it has been theory.

But yes, we've coordinated detections between LIGO and radar astronomy now, and there's no reason to believe gravity travels FTL. As always, there are error bars, but they're tight enough not to get excited about. That is, who cares if gravity travels at 1.00000000000001 the speed of light? (The theoreticians would go absolutely ballistic, but pragmatically that would mean nothing.)

> but pragmatically that would mean nothing

Well except the part where you could use gravity waves to send messages to the past, I imagine that would have some pragmatic implications.

Huh? What about gravity waves allows... backwards time travel?

Anything that travels faster than light is a violation of causality and would be perceived to move backward in time.

Only in our current understanding of relativity, which assumes that it is not possible to exceed the speed of light.

You can’t just break one postulate and assume the rest of the consequences are still ironclad.

> which assumes that it is not possible to exceed the speed of light.

That's... No, that's not what General Relativity says at all. The speed of light as universal speed limit is not a postulate, it is a result.

The reason is because going faster than light would break causality, as I mentioned, meaning time travel, and therefore meaning all kinds of paradoxes. That is why it is generally said that FTL travel is impossible; because the consequences of it being possible are absurd.

If you can send information FTL it creates time travel paradoxes in GR. Gravity waves are a propagation of information, so if they moved at 1.0000001 times the speed of light it would cause… the theoreticians to go ballistic, because it would either open the door for time travel issues, or something about GR is wrong.

At least, that’s my lay understanding of it.

So, nothing specific to gravity waves allows for backwards time travel, so much as anything that carries information traveling FTL would cause backwards time travel.

There’s zero experimental evidence to suggest this.

I actually went down a fairly deep rabbit hole to try and get to why GR proponents believe > C travel allows for “breaking causality”.

It basically comes down to a box plot mechanism they have breaking down when FTL is used, and is absurd.

I’ve yet to see any evidence that FTL would break causality.

This is the answer

Something like a neutrino bean sounds more plausible as a communication medium than gravitational waves

What would be the advantage of that?

Unlike radio waves or light, gravity waves aren't impeded by obstacles like stars, planets, interstellar dust, or anything else that might be out there. Nothing could block or jam them and you'd always have a clear signal.

It takes so much energy to create gravity waves and so much effort to detect them that it's silly to try to use them as a medium of communication.

*For Kardashev Type 1 civilizations like us. (And we’re only 0.74 not even 1)

We are not even 0.01 Kardashev.

~0.73 seems about right. 0.01 is about 1.26 MW.

https://en.wikipedia.org/wiki/Kardashev_scale#:~:text=equiva...

According to the linked page, K1 = 10^16 W = 10,000 TW. We are at ~20 TW = 0.002 K1.

0.01 K1 was a generous overestimate. Strictly speaking, K1 really should be 2e17 W, putting us at .0001 K1.

(600 exajoules/y = 600,000,000 Tj/y, divided by 31.5M s/y = 19 TW. https://www.statista.com/statistics/265598/consumption-of-pr... )

It's a logarithmic scale. The 0.73 value is not a linear scaling but a value given by Sagan's proposed interpolating/extrapolating function:

K = (log10(P) - 6) / 10, where P is power in Watts.

20 TW = 2e13 W -> K = (log10(2e13) - 6) / 10 = ~(13.3 - 6) / 10 = ~0.73

That is a very flattering way to formulate it.

That the Kardashev scale exists does not necessitate that any civilizations will ever reach Type II or III.

But you'd be broadcasting to the entire universe.

Also, seems like you'd get a lot of collisions. Everybody in the universe broadcasting via gravity waves would be doing it on the same "frequency" (so to speak) right?

You'd also be perturbing the entire universe. Unlike radio waves, the gravity waves are going to have a very real effect on the objects through which they pass. If you're using gravity waves to communicate with somebody zillions of light years away, seems like you'd disrupt all the nearby star systems.

No you use the same frequency systems we use now, there’s a whole spectrum of gravity waves to use.

It'll be more likely something subatomic, like they're chain entangling photons, we just don't know how to interpret it yet.

They keep ringing our sun and we never even respond! And now they're just annoyed with us and won't respond when we eventually call back.

we generate gravity waves every time we move something with nonzero mass, don't we?

Yes but not in any practically detectable way.

Can a gravity wave be (in theory) directionally focused ?

Or they exist at a completely different scale than us. Their neurons are the size of galaxies or they live in Whoville in a snowflake.

Neurons the size of galaxies, even if one stipulates them magically coming into existence as early as possible, couldn't have hardly thought "hello" to themselves since the universe began. In the meantime, on that time scale, incredible violence has occurred througout the universe. Round trip times of millions of years for the simplest communications are not feasible in this era of spacetime. You'll need to be waiting many tens or hundreds more billions of years before that is conceivable, in the long quiet dark before heat death.

The snowflake hypothesis is at least in the range of the "things we can't disprove", at least if by "snowflake" you mean neutron star surfaces: https://en.wikipedia.org/wiki/Dragon%27s_Egg Of course, one must consider that I'm citing a science fiction book, with all understanding of what that means. But that is at least one hypothesis I don't think we can disprove at the current time, unlike most other ideas put forth. I'd still call it an absolute long shot, and an even longer shot that such beings could leave their star.

I'm fascinated by the idea that the same creatures can live in the same universe and have very different experiences of it. Ants, cats, and humans are all going to perceive the same objects in very different ways. And only humans can understand what human-specific objects are for.

A cat will see a book as a flat surface which probably smells of its owner and go to sleep on it. It has no other concept of "book." And if it sees an open book it can't see the contents as writing, because it has no concept of writing.

The fascinating part is that a human will see the same object but perceive it very differently because of the added human-specific knowledge and cognition.

Unless you're going to make the very bold claim that humans are the most sophisticated and advanced life in the universe, our perceptions will be limited in an analogous way.

We see clouds of dust and gas, star systems, and random background noise. An intelligence a few million years ahead of us may see the same objects as [symbol] and [relationship] in ways we literally can't imagine.

> Ants, cats, and humans are all going to perceive the same objects in very different ways.

Probably in very similar ways, given how many ways there are to perceive something.

Ants, cats, and humans are all carbon-based lifeforms with eyes, nervous-systems, and brains.

Imagine how a cat perceives a bird vs. how a human perceives a bird vs. how a cloud of neutrons perceives a bird.

That's what I love about the Children of Time series. The skill of the author with immersing you in that truly alien perspective of different biological capabilities, sensory organs, etc. is remarkable.

Me too! And a new one came out in the USA last week. I think it was already out in UK.

Children of Memory it is called.

Downloaded but not read yet!

Dark sector. 85% of the mass of the universe. Those dark sector astrophysicists have a tougher time, since their book keeping is only 15% off, and everyone just thinks they aren't measuring things precise enough.

I think the most convincing answer to Fermi is the dark forest theory. The reason no one speaks up is that there is good incentive not to - you get to survive as a species if you stay small and quiet.

Except we are already violating this by sending things out into interstellar space.

Not just “some things”: Nudes, a mix tape, and directions back to our house.

Party! RSVP.

And a car that doesn't work. Imagine the civilization that finds that in a billion years. They will spend countless hours trying to figure that one out

If you haven't already, read "the 3-body problem".

Yeah, seems to me there'd be a bit of time in there before any civilizations decided it was better to stay silent. But that time might not be astronomically relevant.

We really haven't sent anything that's very 'loud' out into space though. A little probe without even an active transmission process is not a very loud signal. All of the electromagnetic noise we emit is barely perceptible above CMB once you get even a small distance away. On a galactic scale, we have been almost entirely silent so far.

The Dark Forest is a fun idea but sounds so clearly illogical to me for so many reasons:

1. The cost of interstellar travel is so obscenely high that the threat posed by the discovery of an alien species on their home planet would be so miniscule to us and them

2. The cost of remotely annihilating an entire species is so absurdly high as to be obviously impractical and basically impossible.

[Spoiler alert] The Dark Forest by Liu Cixin renders all of this irrelevant by the use of science fiction: it purports the existence of interstellar world-destroying weapons that any lowly member of a species can casually "flick" at a "star plucker" to obliterate them. That is not how physics or reality works.

We don't even send our trash to space because just getting it out of Earth's orbit is so ridiculously expensive, yet we're thinking about sending enough explosives to destroy an entire civilization some 100+ light-years away?

We've already been sent the world destroying bomb. It is an information bomb built on tragedy of the commons to ensure we overheat our planet before we become interplanetary. Its name is Bitcoin.

I guess enough time has passed since major Carter blew up a sun, since people are no longer talking about it

Are you arguing that advances in science that would look like impossible magic to us today are confined to fiction forever? Why do you believe that (1) and (2) are true at every stage of technological advancement in our distant future, which may be the technological present of our galactic peers?

A handful of people today can casually "flick" entire cities out of existence, and enough such flicks could eradicate our species, and even if not it would certainly eradicate many. That would have been an absurd notion to somebody a thousand years ago. But the idea that we'll be able to destroy stars just as easily in a million years is somehow just fiction?

No, I am simply arguing that FTL travel is extremely unlikely since whatever physics we discover in the future will almost certainly not overturn special relativity.

This thinking along the lines of "things in the past that were believed to be impossible are now possible, therefore things in the future that we now believe impossible may actually happen" is pretty poor reasoning. In the past, our understanding of the fundamental laws of physics was quite lacking. Today, although it is incomplete, our understanding of physics is considerably more advanced to preclude a lot of physically impossible things.

> In the past, our understanding of the fundamental laws of physics was quite lacking. Today, although it is incomplete, our understanding of physics is considerably more advanced to preclude a lot of physically impossible things.

To me this just sound like a combination of hubris and lack of imagination. Sure, our understanding of physics advanced so much in the last few centuries. Relatively.

I'm sure we're at least like 20% of the way towards cracking the puzzle of how the whole universe actually works; there's just some kinks to work out, right? /s

The way I view history, in a thousand years everything we "know" now might look like nothing more than once-useful, semi-accurate models for describing the behavior of a tiny little subsystem of what reality actually is. Or, more likely, we won't even remeber why the models of today were ever useful, and the average person (assuming there are still separete "people") will flippantly refer to the scientists of today idiots.

Interesting that you assume physics and engineering are "done" and that there are no unknowns, and that there are no new inventions that will happen moving forward. I don't know any physicists or engineers who believe any such thing.

500 years ago your argument would have been: We cant even get to china in 12 weeks without considerable danger and expense, and you expect me to believe its routine for peasants to do so in 12 hours? That anyone can make a near perfect painting and send it to anyone else no matter where they are in a heartbeat - we don't even make bad paintings of anyone who isn't extremely rich because of the absurd expense of it.

I did not assume that "physics and engineering are 'done'". I assume instead that the known laws of physics which seem to prevent faster-than-light travel hold and are inviolable, despite how smart any species may be.

The analogy with the the argument 500 years ago doesn't apply because 500 years ago we did not have the understanding of physics and chemistry that we have today. Of course we still have a lot of physics left to discover, but it's extremely unlikely that whatever new physics we discover will violate special relativity.

You don't need faster than light travel to cover the entire galaxy. Using it as a roadblock doesn't make sense.

It does when traveling interstellar distances. Even traveling at 10% the speed of light, it would take a ship one million years to cross the galaxy. The energy required to accelerate to that speed (and then decelerate to rest) is absurdly high. Once you realize how large the costs become for interstellar travel, simple economics makes most of these arguments moot. The outcome is not worth the cost for almost anything you want to achieve.

We are about 30k light years from the center and the milky way radius is about 50k light years. So if we sent out probes in every direction we could hit 100% of the galaxy in 800k years.

A 100kg probe at 10% of the speed of light is about the energy of a 20 megaton nuke. Another 20 megatons to slow it down.

It seems very likely that the technology necessary will be developed in the next 100-10,000 years.

Let's say we send 10,000 probes out, each weighing 1,000kg at 10% the speed of light out into the Milky Way. We would do this with the sole intention of destroying an entire planet once we find any hint of even bacterial life? There isn't enough time to phone home to decide what to do with this information, so the probe would have to decide for itself whether or not to commit immediate genocide.

How could any government possibly convince their citizens that this is the best use of trillions of tax dollars (if not quadrillions of dollars), not to mention how can we create a 1,000kg device that can categorically annihilate an entire planet? If the Dark Forest theory is indeed true, why haven't we seen evidence of such galactic levels of destruction? The Milky Way has been around for over 10 billion years. Surely by then there must've been at least one civilization advanced enough to do this in that time. Yet we see no evidence for this whatsoever.

The more you spell this out, the more absurd it becomes from any practical perspective.

I find it amusing that your assertions about what aliens may or may not do completely ignores the fact that the one intelligent species we can observe does all the things you claim no species would ever do. Really drives home the point you are making with your satirical take.

I don't think that's true at all. Humans used to invade foreign lands and decimate the native population, but we did that in pursuit of resources, not as the primary goal (when Columbus sailed off from England, he wasn't sent out with the dictum of "go find other intelligent species and annihilate them"). Furthermore, that is clearly not the case anymore in modern times. As I've stated, we have the technology and military might to wipe many nations off the face of the Earth, yet we choose not to.

Our destruction of the environment is different also. Cutting down the Amazon is a side-effect of our pursuit of natural resource. We do not go there with the intention of killing all of the species there. That is just an unfortunate consequence of our hunt for resources.

The Dark Forest is entirely different. The entire thesis of that theory is an advanced civilization would have the singular goal of sterilizing all other life in the galaxy as the goal in and of itself. There is simply nothing analogous to that in human history.

Lets see, in the last 2 centuries humans have:

Devoted years worth of total resource production to kill each other by the millions over a few square miles of resource poor land.

That was such a popular hit that we threw a sequel that was even more costly.

As a result of the sequel we had several major empires devote trillions of dollars to making sure that we could annihilate our own species just in case one of the others also tried to annihilate the species first. This caused the collapse of at least one empire. People regularly call for the use of these annihilation weapons and it's sheer dumb luck that it hasn't happened yet.

Speaking of annihilation - there have been several large scale attempts at exterminating all humans that fit xyz criteria in the last century. Mostly these are not based on anything other than "exists with DNA slightly different than our own". It seems likely that "exists with way different DNA" and even "exists with a different building block than DNA" could be used as criteria.

If you don't limit yourself to intelligent species, humans have carried out large scale attempts at exterminating several native species. Some I'm aware of in the last couple centuries:

Wolf eradication programs paying bounties per dead wolf.

Same for the american bison. (this one is special because it was also intentionally an attempt to genocide native folks by starvation).

The "smash sparrow" campaign in china - kill all the sparrows because of a misunderstanding of what food they eat.

I guess I could buy your premise that humans wouldn't participate in the dark forest for logical reasons is semi-believable IFF we ignore the things humans actually do.

As I stated, people tried to annihilate each other in pre-modern times. In modern times, we literally try to do exactly the opposite, and we go so far as to pass to laws to prevent this even against countries that stand no chance against us whatsoever.

Give me an example of modern times and now we're talking.

All of the examples you said are so limited in scale to what the Dark Forest actually requires: complete sterilization of all life in the galaxy. To go from "killing bison" to exterminating all forms of life is a gargantuan leap.

It could be as simple as a hedging your bet strategy. You might not even need faster than light travel. The weapon of our destruction in the distant future could have already been launched, making its way from its factory at 99% the speed of light as we speak, simply because the characteristics of our planets suggest a nonzero possibility of life arising. If the bet means your species has no potential predator in the future, then committing all the resources you can to such an effort would be a decent strategy.

I hope I am wrong of course.

Everyone seems to be overlooking that the costs for this are insanely high. This has to be funded by tax dollars. Why should we use taxpayer money to try to annihilate every other single living organism in the galaxy?

The reasoning that "there's a non-zero chance that if we don't, someone else will do it to us" is practically useless reasoning, especially from a policy perspective. That's like saying that the laws of quantum mechanics prescribe a non-zero probability to a planet-sized nuclear bomb materializing next to Earth and instantly exploding, demolishing all life here, yet we don't make policies based on such vanishingly low probability events.

Plus is every sentient species going to be this genocidal by nature? Humans do have a history genocide, but in civilized society today, we do everything we can to avoid war. The United States clearly has the military might to invade any number of nations in the world and easily conquer them, yet we don't for a whole host of totally valid and logical reasons. Heck, we pass laws (I assume for good and justifiable moral reasons) to protect indigenous people even though we have the might to completely obliterate them.

Everything about the Dark Forest is completely impractical when thought through with the smallest amount of sensible reasoning.

I was framing it more like the aliens are the ones launching these weapons, not us, we can hardly get our act together for such farsighted planning. And sure, not every species are genocidal, but some certainly are by nature. We hesistate fighting other humans because they are humans, and we value ourselves more than any other lifeform. But people don't hesitate swatting a mosquito, or dumping bleach on a colony of mold in their shower. My cat doesn't care about slowly and painfully killing the insects it catches. The tree doesn't care if its shade blocks other plants from taking advantage of the sun. The invasive species doesn't care if it displaces the native ones. The virus doesn't care if it kills its host.

Alien life might realize this, that the probability is very high that other life forms really don't care about the continued reproductive success of other life forms, unless there is some lopsided benefit involved. Maybe they aren't even consuming their own resources to act on this goal of wiping out the possibility, however low, of a danger to their species emerging. Maybe they've already sent out some AI controlled probes, that are on distant metal rich asteroids far from their homeworld, autonomously mining, building weaponry, identifying targets, and launching these weapons that will hit their targets millions or billions of years in the future. Such implementation could even outlast the species that initially created it.

There are so many practical problems with doing such a thing. The first is that it's incredibly economically expensive to do so. If the aliens aren't spending their resources, whose resources are they spending? Clearly it must be theirs.

Secondly, the thought of unleashing a civilization-destroying self-replicating AI into the galaxy is so dangerous that I doubt any civilization would do it. Imagine the dangers of that. All it takes is for the AI to misidentify you as "another" civilization and wipe you out, or for these AI to be taken over by another party and turned against you, or for the AI to actually just misidentify you and kill you. The dangers of that far outweigh the benefits in the miniscule chance that the Dark Forest is in fact real.

We don't even understand gravity entirely.

It's entirely possible we will come up with a different theory which is largely consistent with much of what we do know, while still allowing for things that we currently think are impossible.

We know so very, very little.

> the threat posed by the discovery of an alien species on their home planet would be so miniscule

That species, left unchecked, could fill up its galaxy in the blink of an eye, by galactic timescales.

We aren't considering anything in light of what we're capable of. We're considering it through the lens of a civilization hundreds, thousands, millions of years more advanced than us.

For such a civilization, I think talking about the 'cost' of things is somewhat of an abstract idea because advanced automation is surely possible for them. Once I am capable of producing a self-replicating machine capable of strong-AI level cognition all I have to do is release one at the frontier of my empire, instruct it to seed itself as widely as it can, build up massive stockpiles of processed resources and energy, and await further instructions. Such a network would be capable of nearly arbitrary levels of resource utilization, all of which could be redirected into wiping out my cosmic neighbors, since my species's immediate needs are satisfied by a similar post-scarcity system.

If I am capable of such a thing and I choose not to employ the strategy of ruthlessly exterminating all life of which I am aware I run the risk of someone else developing this technology and doing the same to me.

The only possible scenario where this doesn't hold water is if it's somehow advantageous to long-term survival of both parties to cooperate and exchange technology rather than spend resources annihilating each other. I think even the simplest game theory analysis will tell us that can't possibly be true.

> The only possible scenario where this doesn't hold water

There are way too many assumptions baked into what you wrote to make that the only possible scenario where the Dark Forest is incorrect.

You basically assume that the benefits of this outweigh the costs, which is entirely unfounded. You also assume that the technology for this is possible. Just saying "imagine something millions (heck I'll give you billions given how old the Milky Way is) of years more advanced than us" does not logically necessitate any of these assumptions to be true.

And if the Dark Forest is so obviously true, why hasn't it happened yet? Why are we still alive? For a 10 billion year-old galaxy, you'd imagine there's at least one other sentient species out there capable of such technology (if such technology is even ever possible in this universe, which is not yet proven of course). If you believe in the Dark Forest, then you must be indiscriminate about your killing, since one key tenet of the theory is technological explosion. A hairy ape (or even a small rodent) today may be harmless but given millions of years, could be the most intelligent species in the galaxy. So taking this to its logical end would require you to kill all life (even bacteria) whenever it's detected.

> why hasn't it happened yet?

It's a big galaxy. It still probably takes a while to get around to "cleaning up" our sleepy part of the galaxy.

That seems to go against the points earlier about how to a very advanced civilization, the concept of resources is basically nonexistent (due to self-replicating AIs). And the fact that this galaxy has been around for 10 billion years. The way everyone in this comments section is talking, it seems like humans will be able to colonize (or sterilize) the entire Milky Way in a mere tens of millions of years. Clearly this is wrong, or else it would have already happened if it only would've taken 1% of the lifetime of the Milky Way to be colonized. That to me is indication that the Dark Forest is incorrect.

If you're a third-rate civilization (as we are), there may be real benefit to being in a backwater spiral arm way off main shipping lanes.

It might just be that we haven't made any noise yet. All the EM radiation we have ever emitted is barely above CMB once you get out a few light years.

I don’t know if I like either one of your points. For #2 you can find an analogy with nuclear weapons. It would seem trivially presently to use them while ignoring how hard it was to invent and produce them.

What if the risk of allowing another alien species to progress is so absurdly high that vast resources are allocated to create WMD to annihilate them. Then it does become trivially easy unless there’s a MAD/detente system. That’s pretty much the point of the book.

The most convincing answer to Fermi's paradox is that since the galaxy is not saturated with Bracewell - von Neumann self-replicating slow interstellar probes, no civilization has yet launched one, and thus there has not yet been a civilization in our galaxy capable of launching one.

The launch of a working BvN probe is basically a permanent phase change for a galaxy.

What would you expect a BvN probe to do that would make it detectable in distant star systems, or even in our own (mostly unexplored) system?

I firmly believe that the chance humans have been visited by aliens is (admittedly) slim but _not non-zero_. I would say the chance has a few leading zeros of precision, and I understand that the universe is _huge_, but by the same logic, the universe is _huge_.

What does 'visit' mean to you?

While I find it unlikely that aliens have travelled to our solar system specifically to visit humans, I find it incredibly unlikely that human activity have not been detected by a Sentinel probe and that this probe has not relayed this info to its creators.

"Visit" to me means either they entered or observed our solar system with some decent degree of resolution. Enough to get a baseline of information about us, I think.

How often do you imagine that the solar system is being visited?

Radio waves have only been emitted for ~80 years. Industrialisation changing our atmosphere ~200 years. Even if something was persistently monitoring you are relying on “The creators” being within a short distance in light years to even have been notified.

Even being extremely optimistic about the speed of light not being absolute, other than wishful thinking - what makes you think that this scenario is “incredibly likely”?

I think that it is very likely that numerous civilizations have seeded the star systems of this galaxy and others with probes that sit and watch for interesting/threatening things.

The probes have arrived far before humans or even life existed on earth and have been waiting and watching ever since, with some of them possible reporting back to their creators on the state of earth while others still watching without yet sending a message because the state of earth hasn't reached some threshold.

As for if these signals have made it back to the probes' creators yet, I consider that unlikely due to the scale of the universe.

I worry that this is the case. The idea that we’re in some advanced species sphere of influence is a bit unnerving. Given the ability to create deep space probes, it should be fairly easy for someone to keep tabs on a large swatch of the galaxy.

If a species had a mere 1 million year technological lead on us, they’d certainly have nothing to fear and would only need to do a drive by every ten-thousand years or so, to keep tabs on things.

Perhaps more concerning is that we could be in between two competing species and they’re monitoring to make sure the other hasn’t colonized this system.

When it comes to aliens there are many possibilities, and few of them are good for us imo.

At least Oumuamua's light sail will only accelerate it to 15-20% of the speed of light. Unless they have some kind of warp drive we haven't seen yet, that should give us (at very least) 20-30 years before the invasion fleet gets here. Probably much longer.

Unless it seeded a little self-replicating factory on the way by. The invasion force could already be growing exponentially out in the Oort Cloud.

Or not. To paraphrase: sometimes a cigar-shaped interstellar mass is just a cigar-shaped interstellar mass.

Any factory way out there is going to operate exceedingly slowly, innit ? Unless there is power from nuclear, or some other source TBD (to be discovered, by us).

why worry that interstellar drive by visits might be real?

also, might you presume such possibilities are rarely good for us because of implicit recognition how bad we humans are to other species?

How about how bad other species are to other species? Displacement. Hunting to extermination. Dramatic changes in the environment leading to extinctions. Parasitic relationships. All these things that we blame ourselves for are really pretty natural things in terms of life. There is no mantle held by any species to be a conservationist. The name of the game is to extract as much available resources as your genotype allows you to extract from the environment. To succeed at the expense of other life, to subsist off of it. In terms of climate change, us humans have nothing on cyanobacteria, who nearly ended life on earth entirely in the distant past:

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

After reading all sorts of arguments in this thread, I am extremely excited by the possibility of an alien probe passing by. Heck, even if it’s the most horrible kind of alien race - you have to agree - it would be pretty fucking epic to witness the end of mankind in a real-life, sci-fi movie.

And if it’s the loving kind of alien race, that’d be awesome too. Either way, enjoy while it lasts!

I'm happy to live in boring, peaceful times.

lol odds of nuclear warfare never been higher since decades

I, for one, welcome our alien overlords.

They'll likely bring interstellar guns, germs, and steel. And bibles/qur'ans.

You don't sound like you have kids or grandkids.

Just had a kid, hope she gets to see aliens in her lifetime.

Even if in the context of them nuking us out of existence or worse?

Ok bro

There are plausible conjectures that we are most likely alone in our galaxy and will not make contact with another civilization for at least a few million years.

If it had been a probe it is already a dead probe. Otherwise we would have picked up something with SETI.

Still could fetch some useful tech if it could be intercepted in that case. Even the "oh you can do THAT" effect would really help.

Intercepting it is next to impossible due to the Delta-V. Capturing it and bringing it back is even harder.

Check out the short film Rakka by Oats Studios. You might change your mind about wanting to encounter a horrible alien race.

https://www.youtube.com/watch?v=VjQ2t_yNHQs

if an intelligent civilization needs to find if there is another intelligent civilization, it might send out an object like that. If the object gets trapped, someone intelligent is there so check it out. If not, its a pass. Its cheap. Its safer since it doesnt accept or deny that originator is intelligent.

It's also incredibly slow. It also needs a way to send back the data, unless you expect it to slowly return to somewhere "civilized". So there is either tech on board or they have tech capable enough to pretty much just observe us directly.

Maybe as some first contact protocol, by dropping the rock outside a candidates solar system. But again, i'd expect them to have so much better ways to observe.

We humans really have a tendency to see pattern in things. Even after having having seen the decompiled game code being basic RNG, a part of me was still looking for ways to improve my drop chance by me doing things slightly different :D

"having tech on board" - yea but it reveals that the probe came from intelligent civilization.

"expect it to slowly return to somewhere "civilized"." - this one looks good.

An advanced civilization that can send out a probe like that also likely has tools to cloak its existence to us. You could very well have a situation where the mothership docks outside of a solar system, cloaks itself, and sends out a probe, and the probe eventually makes it back to the mothership.

I really think we are limited by our imagination and anthropomorphism. A civilization a million years ahead of us in development is likely capable of things we can’t even imagine.

I always like to remind myself that our own civilization is at most only 10k years old. If we survive, I can’t imagine what we would be like in 10x more time.

This is an important point - that the chance of an alien civ being roughly at our level of technological sophistication is very low. They be either primordial critters (no space travel there) or too cool for the likes of us monkeys.

It's a very narrow window, isn't it? A civilization even 500 years ahead of us might be mind bogglingly advanced.

If you were to travel to the 1600s and tell people that we have generative AI, spaceships, and smartphones, their brains wouldn't be able to comprehend it.

One of the author's conclusions to "find out more" (my paraphrase) suggest a rocket using a gravity well to go after it.

Are there any options for using a Voyager 1/2 or radio based telescopes to observe it? (I'm a CompScience guy - not an Astrophysicist so that's my best way to describe my question)

Voyager 1/2 are both basically EOL at this point so I think at best you could maybe turn the instruments back on for one last hurrah but they're an awfully long way away from Kansas now so even a suicide mission of sorts could overwhelm them.

> Voyager 1/2 are both basically EOL at this point so I think at best you could maybe turn the instruments back on for one last hurrah but they're an awfully long way away from Kansas now so even a suicide mission of sorts could overwhelm them.

I don't even have to look it up to be 100% sure that Voyager 1/2 are in the wrong place, going in the wrong direction, with the wrong instruments to observe Oumuamua. Their batteries are also nearly dead and they never had enough propellant to go anywhere except approximately where they're going now. The best they could ever do is make small corrections to slingshot off something else, and there's nothing to slingshot off of anymore. Also, I think they're almost out of propellant, too.

Here is the PDF linked by the page for those getting 'hug of death' http://uu.diva-portal.org/smash/get/diva2:1721987/FULLTEXT01...

Nitpick: it's ʻOumuamua, not 'Oumuamua. The initial letter is the ʻokina (U+02BB), representing a glottal stop.

https://en.wikipedia.org/wiki/%CA%BBOkina

Well, they don't write Hawaiian, so there's no correct representation.

More clear example would be to write some name a non-latin script at all. You'd have to nitpick that Athena is not correct, and they should've written Αθηνά.

Are there any proposed orthographies for Hawaiian that represent the glottal stop in a different way?

Seeing as the Hawaiian language has only 5 vowels and 8 consonants it seems a shame that they couldn't find a way of writing it with the Latin alphabet that didn't require adding a character which, to the uninitiated, doesn't look anything like a letter. And, in fact, for the purposes of capitalisation, it is not treated as a letter: the following vowel gets capitalised instead. Meanwhile, there seems to be more than one system in use for lexicographical ordering of the ʻokina.

Of course there's no immediately obvious alternative: H is perhaps a natural choice for a Latin letter to represent a glottal stop, but if H were used for the glottal stop in Hawaiian then a different letter would have to be used for the sound currently written with H: seeing as the currently orthography has been in use for some time one would want to avoid an incompatible change. So J, Q, X or Y instead of ʻokina? Hm...

Of course I'm aware that there's probably no point in thinking about alternative orthographies for Hawaiian, that probably there's no demand for a "solution" for this "problem" ... but it seems like an interesting thing to think about for a few minutes anyway.

Seems HN has ruled out aliens but have we given any consideration that 'Oumuamua may have been sent back in time by a future human civilization? That may explain the rather phallic shape.

Hyperion enjoyer?

If Oumaumau is in fact of extraterrestrial origin, it could be the only evidence of life outside of earth that will ever pass through our solar system. We'll never know.

Let's slingshot a probe to it and find out! I'm only half-kidding. I think it would be super worthwhile to do, though. Especially to attempt to solve the mystery of why it sped up by 17 m/s for no visible reason.

They have modeled an acceleration via outgassing. It is quite possible and even likely.

> Open Access in DiVA > fulltext(1312 kB) > 0 downloads

well... either their counter is broken, or nobody needs to read the article to take part in our fruitful discussion

It should be at least one, since I downloaded it, so the counter is broken or delayed.

I believe in aliens from a statistical standpoint.

But I don't believe in interstellar travel at all. I don't think people grasp the distances between stars. The longest distance a human has traveled through space is to the moon. If, for scale, this was about 2 millimeters, then the nearest star would be another 200 kilometers/124 miles away. Here's a great video to illustrate https://www.youtube.com/watch?v=dCSIXLIzhzk

IMO Oumuamua was a rock.

However, it's fun to think about it being alien, and it's remarkably similar to Arthur Clarke's Rama story.

Presumably the speed and trajectory of Oumuamua is known? Has this been traced back to give a potential origin if it is fro another star system?

"Two of NASA's space telescopes (Hubble and Spitzer) tracked the object traveling about 85,700 miles per hour (38.3 kilometers per second) relative to the Sun. Its outbound path is about 20 degrees above the plane of planets that orbit the Sun." https://solarsystem.nasa.gov/asteroids-comets-and-meteors/co...

If the distance to the nearest star is 40,208,000,000,000 then:

40,208,000,000,000 / 38 (km per second) / 3600 seconds per hour / 24 hours per day 365 days per year = 33552 years if it had come from closest star

Do I have those numbers right? Maths isn't a strength.

An interstellar object created by aliens arriving here doesn’t imply interstellar travel, if you meant that to mean “manned craft.”

Yeah, for me this is the sad reality of getting older and replacing somewhat essentially sci-fi fantasies of progression with bleak, mundane reality.

Space is really big. Really, really big.

The impossibility of interstellar travel is perhaps the only fact that I find so depressing that I simply refuse to believe it. The universe is just so much more interesting if FTL is possible. It helps that being wrong about this fact doesn't really impact one's life either way.

Okay, then I'll cheer you up just a bit: interstellar travel is quite possible. In fact it's easy... if you can cold hibernate.

It would be very easy for an AI that could simply turn itself off for tens of thousands of years. It might be a do-able for an alien biological entity with a different biology that finds it easier to survive cryogenic deep freeze, something like a big smart tardigrade.

Managing sleep and wake is pretty easy too. No internal timing mechanisms needed. Just let your proximity to a star do it for you. When you leave the vicinity of a star you have no energy and you go night-night. Your temperature will fall down to as low as a few kelvin. This basically stops time in terms of any chemical degradation, though the most sensitive bits will need to be wrapped in radiation shielding against cosmic rays to prevent cumulative damage over the aeons. When you approach another star the temperature starts to go up and solar power will power everything up.

Interstellar travel is only hard for us because we have short life spans and can't survive being frozen. Unless we can figure out how to successfully freeze a human down to liquid helium temperatures and then revive them it's unlikely that humans will ever leave the solar system.

The AIs we build might though. This would include "uploaded" minds if we ever figure out how to do that.

If anything ever does visit us my money would be on it being an AI.

If you find humans being stuck in the solar system depressing, consider that the solar system is absolutely gigantic and we could explore and settle it for aeons and aeons without getting close to exhausting that frontier.

If anything ever does visit us, long odds are it is spam. Very clever spam.

It would be disappointing if it was an ad for one weird trick for growing your hair back.

Worse if it was for growing back genital tentacles. And, self-executing.

Von Neumann spam?

Imagine a religious order like the space Mormons in the Expanse creating a self replicating evangelism bot. A few billion years later nothing in the galaxy with more brain power than a mouse can get through life without being asked if it wants to hear about another testament of Jesus Christ.

We do help seed millions of other advanced civilizations though since when they become smart enough they are able to learn a ton by reverse engineering some of the millions of dead probes littering their planet and every other celestial body. Their first messages into the cosmos are variations of “okay which one of you bastards did this?”

Nobody is ever able to figure out the meaning of the probe’s message and humanity is long extinct.

Not meaning to diss Mormons though. If anyone built a generational ship I can imagine them doing it.

You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space. ~ Douglas Adams

Have you had a look at Project Daedalus ?

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

Or Project Orion :

https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

and the excellent book on Project Orion

https://www.amazon.com/Project-Orion-Story-Atomic-Spaceship/...

A nice visualisation I like to use is this: if the orbit of the Earth was scaled down to the size of a coin, then the average distance between stars is about a mile.

EDIT: Corrected the maths.

And yet we pretty much have the technology right now to send a probe to Alpha Centauri. The Parker Solar Probe would make it there in about 8000 years. We could probably make a probe that makes it there in much less time if we wanted (by taking much longer to accelerate and de-accelerate). Then it just needs to survive a few thousand years dormant.

We have had limited success at keeping a carved rock dormant and intact for thousands of years.

Not interstellar, but I leave near Sunspot, New Mexico. Since lots of schools visit the sunspot observatory there they have a series of signs starting with Neptune at the beginning of the road (Highway 6563 for those interested) and ending with the sun at the observatory. The signs are spaced proportionally over the 15 mile road and it amazing how close mars -> sun all are compared to the rest, and that doesn't even deal with the rest proxima centauri (I'm curious where that would actually be, Colorado?)

If my maths is right, then at that scale Proxima would be almost as far as the Moon: https://www.wolframalpha.com/input?i=distance+to+proxima+cen...

I dont get why people get hung up on distance. It only takes time to traverse and it isn't exactly in short supply. Whats the rush?

It's a good point.

Humans have existed for about 300,000 years.

Sharks have existed for about 450 million years.

I suppose its possible that humans could exist for hundreds of millions of years? If so then several hundred thousand years robot probe missions might make sense.

> Humans have existed for about 300,000 years. Sharks have existed for about 450 million years.

You’re comparing a species with an order. Great White Sharks for example have only been around several million years.

Ok I see.

One of the arguments for Oumuamua being more than just a "rock" was its detected dimension. If I recall correctly, it was very long and skinny and thus not very rock-like in a traditional sense. I think Avi Loeb put forth the idea that structurally an object like this could be a a piece of space junk. Maybe a piece of a space ship that would be able to be held together while spinning even with a long and skinny dimension. You'd imagine less stable pieces of rock to collapse into themselves and become more sphere like. Oumuamua was potentially a long skinny object that had been spinning around through the universe for a very long time.

Yeah not rock like because it's probably a cosmic dust bunny. An extremely low density object composed of dust with large voids.

Interstellar travel would be possible if we learn how to manipulate consciousness and then transport consciousness as data using light. The first part may be accomplished without continuity for the original but as a seamless experience for the copy.

Looks good to me as a rough back-of-the-envelope calculation to get the orders of magnitude right (the speed will go down as the object is climbing out of Sun's gravity well).

However, you're still missing a guesstimate for alien lifespan. Do you have reasons to believe they live shorter than 33552 Earth years?

Also, is 38 km/s really the top speed for hypothetical interstellar ship?

I imagine aliens that live on average 870 Earth years (~10x average lifespan of a female Japanese) and travel at 9,000 km/s. They can easily make Sun-Proxima Centauri trip six times in a lifetime.

The galaxy isn't static. Sure, right now the nearest star is more than 4 light years away, but wait around a few million years. You'll get stars passing within a fraction of a light year.

Interstellar travel is entirely in the realm of possibility for the future. I'd even call it likely. We'll have to wait a few centuries probably, but we'll do it unless we get derailed or extinct.

On the other hand there are theories around how many alien civilizations there are and there are probably not many if at all. Basically we are "early" and there is probably no other civilization in the milky way.

Advanced aliens could only do space travel and they have no interest in us nor our science.

Something they may need and we have is resources but it's not rare at all in the universe.

I bet they need a habitable planet or they are some kind cult like evangelical chritivans have to spread their religious bullshit everywhere.

These kinds of assumptions are just too strong. What we consider "resources" they might consider peanuts.

Maybe the most rare and fascinating thing to them are our minds, our cultures, and the unique combination of senses and biases that form our semi-consistent conscious perception of the world.

Hugged to death?

Consider the statistics of it being an alien probe. Now consider the statistics of it being a rock. It's a rock.

Stand back, this guy/gal's using Occam's Razor! They'll cut you!

What is that called? Occam's Blindfold?

We don't know it's a rock. We don't really know what it is, other than it's the first thing we've picked up from an interstellar trajectory, is bizarrely shaped, didn't reflect the pull from the sun, swung by the Earth and then accelerated away.

It's Occam's Razor. In order for it to be an interstellar rock, you require no other assumption because there is little evidence to suggest it isn't.

If you believe it is a probe you must assume an alien civilisation.

Occam's Razor suggests fewest assumptions win.

Except the whole discussion is still here exactly because there is evidence to suggest it isn't a rock.

Supposedly it accelerated a bit, inconsistent with what we know about how rocks move through space.

I made a “play on words” to convey the notion of discarding data in the insistence on coming to a conclusion rather than simply holding ambiguity.

No decision needs to be made. We don’t know if it’s a rock or anything else and that’s ok.

You don't have to believe it's an alien probe to accept the substantial evidence that it's not a simple rock.

There is no such "substantial" evidence. If there really was scientifically agreed upon "substantial" evidence, then it would be world-shattering news.

Why? It's some weird object that's not a simple rock. Most people don't see that as earth-shattering, just weird.

The basic weirdness is this: it didn't move like a rock, and anything normal that outgassed from it would have been visible, but it wasn't.

There have been a couple hypotheses for weird things it could have been made of, but those ideas look unlikely for their own reasons. One for example was that it was frozen hydrogen, but that would have evaporated in interstellar space. The earth has not shattered because most people assume there's a reasonable explanation that nobody's figured out yet.

A better reframing of the same concept is scientific parsimony, which suggests a heuristic for economical empiricism. Occam’s Razor suggests to people that probability is somehow being calculated.

The delta-V from non gravitational forces was only 17 m/s or 38 mph. By comparison it has a hyperbolic excess velocity of 26.33 km/s and its maximum speed was 87.71 km/s. Its "maneuvering acceleration" amounted to 0.02% of its maximum velocity. That is all consistent with some combination of radiation pressure, solar wind and offgassing. Its closest approach to Earth was 0.1618 AU which is not terribly remarkable, it isn't like it did a close flyby in between the Earth and Moon or something.

We also now know that planetary systems are incredibly common, it is almost certain that Oort clouds are incredibly common. And while stars rarely collide, they do commonly come close enough to gravitationally interaction, and it is likely that material would be flung into interstellar space by that. Our imagination of interstellar space being just gas and dust and otherwise empty is likely very incorrect.

Thank you. I stand corrected. And yet... you have to admit it’s intriguing...

It is intriguing because it may have been ejected after a star went red giant and stripped most of its volatiles from it, a billion years ago and wandered across the galaxy very slowly until it first encountered our solar system. It would have been incredible to be able to put together a lander mission, but the direct delta-V to rendezvous would be ludicrous.

A fast fly-by would not have been though, if it had launched as soon as we saw it.

A “direct intercept” like you’re suggesting gives you very little time to take any measurements even if we had a vehicle standing by. For now it’s not the kind of mission NASA has chosen to fund just in case they got the opportunity to scramble a one time fly-by mission to collect a few seconds of data on an object that happened to streak past us this millennia.

1.618.....

The wikipedia citation for that lists 24,000,000 km (0.1604 AU) and 15,000,000 miles (0.1614 AU).

The wikipedia article for that is overly precise and lists 24,200,000 km (0.16176700836 AU) and 15,040,000 mi (0.16179731467).

What caught their eye is that 1.618 is the Golden Ratio.

Yes, I just explained how that wound up there.

Basically, the universe is a big place for accidents to happen in, so they do.

The wikipedia edit was not an accident.

sounds like somebody wag tweaked the entry to make it come out as the golden ratio.

This argument doesn't work, because you don't know the statistics of it being an alien probe.

That's not how it works: you start with the null hypothesis and you try to see if you can reject that with some confidence interval. In this case, the null hypothesis is that it's some kind of ordinary object, and its path is determined by gravity, radiation pressure, and outgassing. Only if you can demonstrate why this is highly improbable can you start talking about alien probes.

As others have argued in this thread, once you do this kind of analysis there's nothing left that is odd and needs explaining.

Wasn't the whole thing about that it didn't move like a rock?

So... any statistics on rocks that can accelerate on their own?

What are the statistics of rocks that behave like rocks?

What are "the statistics of it being a rock"?

Of all the interstellar objects like this one we have observed, how many were rocks?

How can we consider those statistics if we don’t know how common alien civilizations, or their sending of rocks, is?

I'm not sure what it is, but I'm in the camp that it's most likely a rock. But a very interesting rock! Especially considering it changed its trajectory but not its spin. It's extremely unlikely to be a probe because it's heading in a different direction from where it came from. And if it's an interstellar traveler, it's probably going too slow, or at least hasn't bothered to pick up speed as it exits.

I don't think we'll ever truly know enough about it. Even as just a rock, there's a ton to learn there! And sadly we'll only ever have a small slice of data about it.

Obviously it was ejected mass used to reduce the velocity of the invasion vessel due in about 75 years.

This is disingenuous, an example of twisting statistics for your own karmic gain.

The fact is, if you consider the statistics of it being a rock that also behaves in the peculiar flight pattern that this thing took, it could very well be a probe.

Katz's attempts to delegitimize Loeb as a scientist makes his argument less credible. Aliens or not, it's disingenuous to deny that some aspects of Oumuamua don't yet have satisfactory explanation.

Scientists are people subject to the same foibles as the rest of us.

But, the abstract promises a direct challenge:

> one of them is Jonathan I. Katz who challenges Loeb’s hypothesis directly

It's a passive aggressive funding fight. Just politics and business. I'm pretty sure Loeb isn't as crazy as his latest claims make it seem, but without outlandish bold claims no one will fund future observation and scientific work on it. At least that's been my take on Loeb's behavior.

"Doesn't yet have a satisfactory explanation -> Must be aliens" has a long history, long enough that the rest of us are entitled to draw the inductive conclusion that it's a weak argument very unlikely to be true.

It is inductive, not deductive, so this bothers people laboring under the misapprehension that science deals with deductive reasoning. But science is ultimately inductive; we happen to sometimes get to deduce things within its framework but it all lives in an inductive framework.

That's just one step down from "Doesn't yet have a satisfactory explanation -> Must be supernatural.'

Clearly we need to launch Bezos, Musk, and Branson toward this object so they can inspect it for us and radio back what it is.

There's a joke in there somewhere about what they will radio in and what you will make of their reports...

Bezos - it's wonderful! Something something wage suppression..

Musk - something something free speach...

Branson - My God! It's made of stars!

Slightly off-topic but I find it incredible that people in the comments think interstellar travel is impossible (or almost impossible)

A couple centuries ago, the brightest minds thought that humans flying in the air would take a million years. How can humans travel to the other part of the earth within a month? Today, it takes 16 hours (4 of which are airport security).

A century ago, almost everyone thought that stepping on a divine body like the moon is absolutely impossible for humanity. We did it less than 80 years after inventing aircrafts.

A century ago, everyone thought it was impossible to fling a tiny device to blow up an entire city. Hiroshima and Nagasaki...

Now, we think that it would be impossible to travel very long distances in space. Well, this challenge seems a piece of cake compared to flying in the air, walking on the moon, or generating unimaginable energy from atoms.

My layman solution to interstellar travel is constant acceleration using controlled nuclear fusion. We can use interstellar dust for necessary matter for our nuclear fusion (lots of hydrogen in interstellar dust). Even if we can't use interstellar dust while travelling, we can certainly carry enough from our solar system.

I read somewhere (don't remember where) that if a ship constantly accelerates in space, it can reach another star system in a few decades and another galaxy in less than a century.

It's definitely a trivial challenge for humanity compared to what we have accomplished in the last 2 centuries. What do you think?

Interstellar travel is downright easy on time scales of hundred to thousands of years. We just need to make humans last long enough.

[1]> According to wikipedia, interstellar travel at 1G would take approximately 1 year + the distance in lightyears. Proxima Centauri (4.2 light years) for example would take 5.2 years.

This^ is from the traveller's standpoint. I am not completely sure about how long it would take from the perspective of someone on Earth. But this definitely seems plausible if we can solve the other problems with constant acceleration such as sufficient fuel and protection from interstellar dust (at close to light speed, dust would hit with unimaginable force).

[1] https://space.stackexchange.com/questions/840/how-fast-will-...

Maintaining a 1G acceleration for years is either impossible or so hard it may as well be impossible. Even if you had a magic drive that could do it you would soon reach velocities where colliding with the smallest spec of dust would be like a small nuclear bomb. 1G to Proxima Centauri would reach a peak velocity of .95 c and hitting a 1g particle would release 48451 tons of TNT of energy. So you would need BOTH a magic drive and a magic shield.

If interstellar travel is as "trivial" as you argue, then the great filter starts to look a lot more scary to me.

With the assumption that interstellar travel is trivial for a sufficiently advanced civilization, Fermi Paradox becomes a true problem. The best solution for Fermi Parafox, in my opinion, is interstellar travel being impossible.

I don't think Dark Forest is possible because consider how different our thought process is from any other life form on Earth. And due to butterfly effect, every civilization's thinking will be completely different. The chances that every civilization will converge their thinking into dark forest seems impossible. Some stupid civilization is bound to broadcast their existence and location. Some other stupid civ might try to control all galaxies using self-replication (exponential growth). So we should have seen some such sign (considering how many alien civs are likely to be there)

Great Filter is another possibility. But it feels unlikely : there are trillions (10^12) of galaxies and trillions (10^12) of planets in each galaxy. So a total of 10^24 (1,000,000,000,000,000,000,000,000) planets out there. Consider the number of civilizations. Is it possible for every single advanced civilization to be destroyed by the Great Filter? If it is, then it must be one hell of a filter. I am very excited to find out what it is, if it happens in my lifetime.

> I read somewhere (don't remember where) that if a ship constantly accelerates in space, it can reach another star system in a few decades and another galaxy in less than a century.

The problem is, it also has to slow down and stop at the destination. To do that, it would have to take all the deceleration fuel with it, and the amount of fuel needed goes up exponentially with the amount of deceleration required.[1] There’s no known or even theoretical form of propulsion with the specific impulse needed to get us to the next star system in under 600 years.

[1] https://en.m.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

I skipped over deceleration because 1) our probes can transmit something significant about a galaxy even at that speed and 2) over time, we can probably figure out a way to decelerate using a galaxy's natural resources (similar to how we use a planet's gravity for slingshot)

Surely, given a century, our scientists will figure out something.

There aren’t any resources in interstellar space. It’s a near-perfect vacuum and the temperature is a uniform 3 Kelvins.

There are huge swaths of interstellar dust (mostly hydrogen) which can be used to slow the probe down.

If not, then we can use a galaxy's resources to slow us down. Basically a complex version of planetary-slingshot.

My argument is, given a century, we are likely to be able to find some way to decelerate. Consider our accomplishments in the last century (airflight, spaceflight, computers, nuclear, internet)

Sorry this may seem a little snarky but - "They will think of something" - the universal band-aid for I want it to be true but I rationally don't know how.

When ever I hear that, the optimist in me wants it to be true. The pessimist thinks otherwise and nowadays the pessimist usually wins.

We will have hotels in orbit by the 1970's - they will think of something! That was a legitimate thing that the Hiltons proposed back in the 1960's.

I used "they will think of something" as a all-encapsulating solution for what humanity will do in the next century. Predicting the next 10 yrs is almost impossible, let alone the next century.

Your example of hotels in orbit is an incorrect example. If humanity wanted to build a hotel in orbit, we would have a hotel in space (we already have a crappy hotel - ISS). I don't consider Hilton's incompetence to represent humanity's incompetence.

I don't want to defend the Hiltons but that is just one example of something that was very common during that time period. In the 50's/60's - the idea that we would not solve the fundamental issues of the era over the coming decades would have been laughable.

When it comes to material shortages, fusion power, limits of computer chip scaling, global warming, over fishing, plastic waste, hyper effective battery storage, nuclear deescalation etc... have all been answered a lot with - they will think of something. Yes, there have been improvements but with most of these things, we have also missed the mark by a long shot. And decades later, we haven't. Sometimes it is right, look at what we did with CFC's. But it is by no means something I would hitch my wagon to.

John Michael Greer calls phrases like these 'Thought-stoppers' Little saying that we have that mean we don't have to face the ugly truth of something or are just trying to be a little too optimistic about the future in the face of hard times. "Housing prices only go up", "They will think of something", "Stock prices only go up", "It is different this time", "The fundamentals don't matter any more" etc.

If it is just a probe that blasts past, that does not count as interstellar travel.

There would be very little left of a vehicle after being blasted by relativistic hydrogen nuclei for 3M years on its way to Andromeda. And, who would be listening for its report 6M years later, if it could get to Andromeda intact? Or even 500,000 years later, from one of the Magellanic Clouds?

It would make sense to gather up your whole civilization and set out at a statelier pace, perpendicular to the galactic plane, to get clear of the numerous hazards that all threaten to sterilize your whole solar system when you are in the thick of a galaxy. Then it wouldn't matter if it took a million years to get clear. Probably you induce a polar jet from the sun for propulsion, and bring the whole solar system with you. (You would leave the Oort cloud behind, sadly.)

The amount of energy required to beam a signal through galaxies far exceeds the capabilities of any probe.

Using fusion for interstellar travel could work, but it would be extremely slow due to the low availability of fuel. Maybe it could be done for synthetic lifeforms or cryonic preservation. Generation ships and such are out of the question though.

> low availability of fuel

Isn't hydrogen one of the most common elements in the universe? And nuclear fusion needs only hydrogen (technically deuterium and tritium, but where there's hydrogen, deuterium and tritium will also be there)

Sorry, no tritium.

Magical thinking unfortunately.

what is magical thinking? Interstellar travel being possible or impossible?

I think the big thing is that all those original achievement don't defy physics to achieve them. It was a case of ignorance and the belief that we just were not that smart. And while there was a big period of exponential growth - there is an upper limit.

We aren't going to Galaxies in a few hundred years - the time to Andromeda is 2.5 Million Light Years. Unless we fundamentally have physics wrong, we aren't doing that any quicker no matter how hard we try.

2.5 million years earth time but ship time is totally different.

Imagine being blasted with 2.5M years' worth of relativistic IGM protons in only a few years of ship time.

Side note: Sorry to spoil the apparently impeccable record, but for completeness:

A half-century ago, civilians could experience supersonic flight. Well, it has since become impossible.

A half-century ago, people walked on the Moon. And not once since.

Just a reminder then that unfortunately the passage of time alone is insufficient to guarantee technological progress. Now, let's get back to work, I guess...

you are right about this, but my argument is that we can do this if we want to. Whenever humanity set its sights on a big project such as Apollo or Manhattan, we have accomplished "impossible" things.

Human history is one of both pessimism and optimism. Definitely the optimism of the US in the 1950s and 60s was helped along by the destitution of the Great Depression (1930s+) and WWII. And there was still a lot of suffering and reason to be pessimistic in that time. (And the 30s were a direct result of the 20s.)

I’ve also seen the studies on human cycles suggesting a link between how long ago a period of massive suffering occurred and the propensity for people to entertain ideas likely to bring about great suffering. Simply, people unable to forget the horribleness of war will fend off the little and big things that can lead to war much better than people who have never seen war.

I hope humanity can regain some optimism and direction without having to go through a world war. Or similar.

I find it worrying how much modern fiction is dystopian. I would call Game of Thrones dystopian, for instance, and it was immensely popular. Utopias like Star Trek are often ridiculed, for counterpoint.

Granted, internet comments are generally worthless. The signal to noise ratio in HN comments has gotten extra horrible of late, for that matter. It could be just the low lying fruit for people to get upvotes. But it degrades the site.

Absolutely. I wonder if say, cheap energy, will be as readily available for non gov / army purposes in 50 years.

The comment your responding too sound like someone born in the 60´s or 50’s. ( meaning : tech is always progressing, no limit, forward and upward . It’s nice. But I don’t think it match 2023 )

Energy is available more cheaply now than at any time in history, and the cost is still falling at an exponential rate.

You can just set out a solar panel and collect hundreds of watts. The only way that could be lost is if civilization collapses so solar panels can't be made anymore. Even if that happens, most of humanity would quickly starve, and whoever is left would find plenty of panels to salvage.

Solar panels require some pretty advanced supply chains, but anyone with an engineering textbook, some wire, and some bamboo can gather a few kW of wind for years with a few weeks work.

Yes, it is absolutely the cheapest in history. Or maybe that was in 2008 actually, when the oil producing countries organisation let us know that we reached peak oil production. Most likely that was the cheapest in human history.

What I’m saying is that it’s not going to be cheaper.

We’re gonna have to work more and more for it. That’s fine.

Back to the solar panel. Can we produce, operate, service them at scale without the support of cheap petrol?

Can we sustain the industrial process without the gas to carry stuff from one place to another?

Can we build those solar panel in a lighter industrial society?

I think so yes. But we need to be drastically more frugal.

Specially in place like North America and Western Europe. I also welcome that as a nice change.

To put some context : let think about the effect of COVID-19 on the global logistic. I think that was not even a warming round.

More specifically to your point :

- yes, you can collect hundred or watt during the day. Again, it’s great.

- yes, you can salvage them and operate them. For 10 years. Then you need to find a fabric of photovoltaic cells to replace them :)

For example of low tech long term energy I would rather pick wind ( basic wind turbine ) or water ( good old dam and turbine )

My point in one sentence : solar is great, but you need the whole modern industrial complex to use them and that complex is about to be shocked by the scarcity of gas.

Solar and wind are still getting cheaper, with no end in sight. Solar, in particular, will soon drop below $10/MWh. Printed thin-film perovskite cells delivered in rolls will sharply undercut prices for rigid panels.

Silicon cells last well beyond 30 years. Even after 40 years, most will still produce 80% of nameplate power; longer if they are kept cool by floating on reservoirs.

Manufacturing relies on energy available. That will increasingly come from renewables as that fraction of generation increases, so dependence on fossil fuel for that will fall in direct proportion. Transportation still relies on petroleum, but it will soon be cheaper to synthesize fuel using renewable energy; ocean shipping will move to ammonia.

There is no scarcity of gas. There will instead be a surfeit as demand falls off, to the point where it will not be worth extracting at a price competitive with renewables. It will still be used where its carbon is needed, although it will see competition from captured carbon.

We do not need to be frugal. We just need to build out renewables faster.

> there is no scarcity of gas.

Is gas not by default, scarce? In the sense that we know that their is limited reserved ? ( as opposed to infinite reserve of solar energy for instance )

I thought OPEC was more clear on that, I found peak oil date in the 2030/2050 range. My understanding was that it was behind us already. Good.

What about storage of solar? We know demands is higher when production is lower ( during winter, in the evening after work and so on )

Don’t we need a second source to complement with something like gas/coal/nuclear ?

> shipping will move to ammonia.

Never heard of it. Great.large ship do consume a lot and our logistic need them.

>A century ago, almost everyone thought that stepping on a divine body like the moon is absolutely impossible for humanity.

A century ago we DEFINITELY conceived of visiting a divine body. 121 years ago a science fiction movie about landing on the moon was released, based on a scifi book released _158_ years ago.

>if a ship constantly accelerates in space, it can reach another star system in a few decades

Try a few dozen thousand years, my dude... https://www.universetoday.com/141407/how-big-would-a-generat...

Even Project Orion, which is literally strapping many successive nuclear bombs onto the bottom of your craft, would take 130 years to get to our closest star.... and that's not taking into account stopping time, so it'd take 130 years to do a flyby of Alpha Centauri at 3% of the speed of light.

Not to mention the fact that ALL spaceships bleed air even under optimum conditions. A generational ship would need to be HUGE and have even bigger reserve supplies of air and water than you'd ever think possible. 50,000 years worth of air and water for 100-500 people? That's a LOT of mass.

Beyond ion propulsion and Project Orion we start to get into wormholes, black-hole-gravity-assists, remote-quantum-entanglement, time travel. Stuff that's theoretically possible kinda sorta if you completely ignore some fairly fundamental laws... the tricky thing is EVEN IF you choose to ignore those fundamental laws, the amount of sheer energy you're talking about is like the many multiples of the energy output of our sun over its _entire lifetime_.

> A century ago we DEFINITELY conceived of visiting a divine body. 121 years ago a science fiction movie about landing on the moon was released, based on a scifi book released _158_ years ago.

I said "almost everyone". If you go to 1920s and ask a million people if humanity will be able to walk on the moon within their lifetimes, not a single one would say yes. And yet, we were able to do it. Similarly, we have been conceiving of interstellar travel for decades.

> Try a few dozen thousand years, my dude

With constant acceleration, ship time is very different. With constant acceleration using controlled nuclear fusion, we can do it in less than a century. Project Orion is not constant acceleration. Now before you point out issues in constant acceleration, remember that if you were in 1920s, you (and I) would also point out issues in moon landing. How can humanity ever leave Earth's gravity, go accurately to the moon, decelerate, LAND without crashing, walk, LAUNCH from moon again, go accurately to the earth, handle extreme atmospheric temps, and LAND without crashing.

Well, we did all of that. So surely, given a century, we can figure out interstellar travel.

I suspect you're getting ion propulsion confused with nuclear fusion. In order for deuterium and tritium to be useful for fusion, you're going to need kilograms of it, not individual atoms. And tritium is required to be radioactive for it to be useful for fusion, but it has a halflife of about 12 years, meaning any fuel we take with us will be useless pretty quickly. And that's even before you take into account the idea of "constant acceleration"... some sort of magical sustained explosive reaction that would go on for 100 years? And that's after sourcing the unobtanium required to shield/support the "constant" detonation.

I suspect you're thinking of an ion drive, which uses fancy magnets to accelerate mass (pea-sized pellets all the way down to individual molecules), which is a slow start but is fine for constant acceleration over tens or thousands of years.

The problem there though is that the acceleration is SLOW, much less than 1G, hence the 20-80-thousand-year estimate to get to our closest star.

>If you go to 1920s and ask a million people if humanity will be able to walk on the moon within their lifetimes, not a single one would say yes.

I'm not sure I agree with that. Spaceflight and lunar (and even Martian!) colonisation was a pretty common scifi idea by 1920. Cars and planes were already 20 years old by that point. If you asked a million people in 1920 I'm pretty confident you'd get a decent chunk of people saying "yes".

Try this : https://en.wikipedia.org/wiki/Project_Daedalus

Also, I agree that the idea for interstellar travel has some holes. Let me rephrase my argument as follows : for every accomplishment of mankind (airplanes, spaceflight, moon landing, nuclear, computers, internet), there have been just as many critics claiming that it isn't possible (they had their own set of reasons). And all of these technologies were much more infeasible compared to interstellar travel (and yet we did that).

5 years ago, would you have imagined ChatGPT or Stable Diffusion? Tech moves fast. There is no doubt in my mind that in a century, we will see interstellar travel like we do airplanes today. But this may well be wishful thinking because I really want this to be true.

>Project Daedalus

That's not a manned craft, which is what we've been talking about so far. It also doesn't have the deceleration stage - Daedalus would flyby Barnard's Star at 12% the speed of light. If you hit a rock along the way at that speed, you're not gonna get any pretty pictures :-)

>5 years ago, would you have imagined ChatGPT or Stable Diffusion?

Absolutely! I think most people in my industry would have imagined ChatGPT or Stable Diffusion as they appear now 20-30 years ago, let alone 5.

>And all of these technologies were much more infeasible compared to interstellar travel (and yet we did that).

See... again, most of the problems faced by the "smaller" feats like airflight are engineering problems, not "this breaks Einsteinian physics" problems. When you're talking about interstellar flight you're running up hard against many fundamental constants of the universe, not just "we can't do that yet"

Any serious fusion proposal will breed tritium. Power to weight is going to be abysmal though.

Also slow acceleration is not the millenia long problem you're making it out to be, 0.01g will get you to 0.1c in under a century. Ion drives are largely limited by the weight of the power source even with current tech.

Any fusion reactor capable of working without prohibitively large radiatiors will have enough control over the plasma to just eject it for thrust directly. ISP will be your limit, not thrust.

Q-drive is a fairly compelling proposal compare to other options. Use some kind of magnetic solar sail to soar along the heliopause until you can make the trip in decades.

>0.01g will get you to 0.1c in under a century

Okay, cool, but that's TWO centuries including the flip-&-burn halfway through.

Also, an NSTAR thruster gives 0.000092 m/s2 for a single-ton payload. That'll take roughly 10,000 years to get to 0.1c, not 100 or 200 years.

I agree with your conclusion, but I always find that these discussions miss the role of medical science.

The key parameters governing feasibility of human interstellar travel are the average human lifespan in years and typical interstellar distance in lightyears. These are roughly 72 years and 5 lightyears, respectively. So it takes about 70% of a human lifespan to travel a typical interstellar distance at 10% of the speed of light. This is... not great.

The key realization is that the relationship of these two numbers is in a sense an accident of biology and astronomy.

It is usually assumed that future technological progress might enable travel at a large fraction of the speed of light, but it is often missed that future medical progress might extend human lifespan to say 400 or 1000 years.

A scarier realization is that intelligent aliens might have natural lifespan that make interstellar travel seem far more practical.

https://cantrip.org/slow.pdf

Human hibernation should be able to solve that problem. I know I am asking for too many things but the challenges for the Apollo mission were even more extravagant.

They had to figure out how to launch from earth's gravity, go exactly to the moon, decelerate, land without accident, launch back again, go exactly to the earth, decelerate and land without accident. Atmospheric reentry is almost 25000 degree Celsius, hotter than almost anything we had ever experienced.

So, given a century, surely medicine will figure out hibernation. And then humans can continue their lifespan when they reach their destination.

I think the difference is that your historical examples of skepticism (which are a bit exaggerated, btw. Da Vinci was a pretty bright guy who thought human flight was possible; Churchill summed up the current understanding of nuclear physics 99 years ago as "Might not a bomb no bigger than an orange be found to possess a secret power... to concentrate the force of a thousand tons of cordite and blast a township at a stroke?"; Konstantin Tsiolkovsky described the science of space travel by rocket in The Exploration of Cosmic Space by Means of Reaction Devices back in 1898)... your examples of skepticism are based on ignorance, not science. As far as I'm aware, nobody ever had a scientific rationale to think humans couldn't achieve flight. If so, it was obviously extremely flawed. We have well-supported science to support the idea that interstellar travel at human timescales isn't possible.

But any scientist will also tell you that there are potential methods to achieve interstellar travel that are consistent with our laws of physics. It's just that, unlike your examples, it's not a matter of human ingenuity to find them. It's a matter of the very nature of our universe whether things like wormholes or negative energy exist or not.

I think the situation with interstellar travel is well summed up in this conversation between TARS and Cooper as they attempt to dock at Endurance (intentional pun hiding in movie title):

TARS: It's not possible.

Cooper: No, it's necessary.

It seems impossible, but if we don't pull it off we die. And I don't mean we the few folks on HN. I mean everyone.

Earth is a graveyard of species. Nearly all (99% IIRC) species that ever existed have gone extinct (most before we showed up). As a species, we can't stay here and live. A 9-mile thin layer of gas over a single small planet is just not a reliable long-term basis of survival. In fact, the fragility of our tiny little habitant is on display right in front of us this century.

tbh I never really understood that conversation. TARS is a machine and if it's impossible from an advanced machine's standpoint, it's impossible from a physics standpoint. Cooper's maneuver was pretty simple that TARS should have been able to simulate and figure out.

Regardless, I agree that being multi-planetary is absolutely a requirement for humanity. We are too risky here. And the risk is not from outside. Humanity has survived for 100s of millions of years without as asteroid annihilating us, and I don't see it changing now).

The biggest risk to humanity is humanity. We will probably figure out a way to destroy ourselves, either with something much more powerful than nuclear bombs or some new unimaginable tech.

Single planetary system isn't much more of a protection than a single planet against some of the possible extinction events, e.g. ones associated with the activity of the Sun or intelligent aliens.

> Humanity has survived for 100s of millions of years without as asteroid annihilating us, and I don't see it changing now).

Homo sapiens is thought to have existed for mere 300,000 years. Our last common ancestor with the chimpanzee [1] existed no more than 13 million years ago. K-T extinction event [2] that wiped out dinosaurs happened 66 million years ago. There have been numerous extinction events before and after that [3].

On the timescales of species this planet isn't safe. At these timescales rare events become regular occurrences.

[1]: https://en.wikipedia.org/wiki/Chimpanzee%E2%80%93human_last_...

[2]: https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_e...

[3]: https://en.wikipedia.org/wiki/List_of_extinction_events

That’s a very anthropocentric, exceptionalist take.

Earth is as much a graveyard as it is a womb and a home and a paradise.

It’s frail compared to what’s outside of it. But it has quite a record (the only one known so far) of making life possible, for millions of years.

There’s nothing we know of this scale and capacity and resilience and welcoming to us (not only humans).

Every time this topic comes up somebody suggests constant acceleration, and every time somebody has to point out that even if you don’t want to decelerate the relativistic rocket equation is still a very harsh mistress. Remember you don’t just have to carry the fuel to accelerate your payload, you have to accelerate the fuel as well.

You may say, “Oh, but I could use a laser to accelerate my craft, that way I don’t need to carry the fuel on board,” and the amount of energy required is still going to be a hell of a lot more than you think.

There’s one thing about interstellar travel you should bear in mind. If you plan on visiting an alien world you should take into consideration the time needed to decelerate. And once you start decelerating, time dilation will gradually stop and you’ll spend an eternity getting to your destination.

A couple centuries ago, the brightest minds thought that humans flying in the air would take a million years.

Two centuries ago humans actually flew.

A century ago, almost everyone thought that stepping on a divine body like the moon

Nobody seriously thought the moon was a 'divine body' a century ago. The rocket equation was known and understood to form a possible theoretical basis for interplanetary travel technology.

A century ago, everyone thought it was impossible to fling a tiny device to blow up an entire city.

HG Wells thought it was possible as did many others.

https://www.bbc.com/news/magazine-33365776

"Churchill grasped the danger of technology running ahead of human maturity, penning a 1924 article in the Pall Mall Gazette called "Shall we all commit suicide?". In the article, Churchill wrote: "Might a bomb no bigger than an orange be found to possess a secret power to destroy a whole block of buildings - nay to concentrate the force of a thousand tons of cordite and blast a township at a stroke?""

We think it's very difficult compared to the challenge of flying through the air or walking on the moon or generating energy from atoms in part because we understand those past challenges and can reasonably compare it to something like interstellar travel. It is decidedly nontrivial.

Imagine the solar system as a guitar, now imagine a gravity rich "visitor" (like a ejected jupiter/saturn) plunging through, plugging on the gravitational relations string set. How long could you hear that sound revebrating, and could you untangle it if it happened multiple times? Could such a "visitor" suspend the gravitational shielding by the outer gas giants?

It should actually be doable with a de-convolution operation, once you compute the gravitational "click" accoustics of the solar system.

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