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.
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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:
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.
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 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.
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.
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.
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 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.
I guess enough time has passed since major Carter blew up a sun, since people are no longer talking about it
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.
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.
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.
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.
If you haven't already, read "the 3-body problem".
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?
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.
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.
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.
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”?
"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.
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?
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.
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.
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)
This is the answer
Something like a neutrino bean sounds more plausible as a communication medium than gravitational waves
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?
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 ?
It'll be more likely something subatomic, like they're chain entangling photons, we just don't know how to interpret it yet.