The next time you address a package to someone, err on the side of caution and append "Earth, Solar System, Local Interstellar Cloud, Local Bubble, Gould Belt, Orion Arm, Milky Way, Milky Way Subgroup, Local Group, Local Sheet, Virgo Supercluster, Laniakea Supercluster, KBC Void, Observable Universe, Universe", to help the package carrier disambiguate.
It'll work fine as long as the babelfish understand not to transliterate place names. Human history is chock full of this: "Istanbul" just means "within the city", "Zhongguo" (China) just means "the land in the middle", "Ohio" and "Mississippi" are just two different ways of saying "the big river".
The other side to this is that given enough time, some civilisation will be oblivious to the rest of the universe. Their visible universe will just be their own galaxy.
The problem is that at such timescales, the CMB will have shifted sooooooooo much that there’s nothing they will be able to deduce, all light has redshifted to absurd scales, and worst of all, everything will be so far away that light will never reach the galaxy.
If their physics is correct, they will figure it out. We did because we verified that expansion is accelerating even though our physics are incomplete. Until the late 90s, physicists accepted a cosmological constant of 0, which meant no acceleration. Turns out that that was wrong.
It may be possible that they figure it out via Quantum Mechanics because it seems that acceleration of the universe is related to the energy density of a vacuum / empty space. The problem is that they won't be able to empirically verify that I think.
The physical continuing expansion of the universe eventually causes any photon to be so far redshifted as to be unobservable, so it actually goes the opposite way. One day long from now, an alien civilization might look out into their night sky and only see their galaxy, and be completely unable to tell the previous history of the universe from observing the sky.
There's also a possibility that a sizeable fraction of all stars exist in the intergalactic medium [1], having been ejected from the galaxies where they formed due to galactic collisions or encounters with their original galaxy's supermassive black hole. A civilization evolving around one of these stars in the far future would be totally unaware of the universe outside their own solar system due to cosmic expansion.
There are probably hundreds of possible answers to that, depending on which aspect you're interested in, ranging from "God" to "gravity" to "42" to "because" to "I dunno".
at risk of being too tautologic: Because for us this is "so many". Because of that we try to compare the scale of the universe with the amount of sand on earth etc etc. At least for me, that type of information does not give me a "better" idea of the problem at hand other than "duuuuuuuuude what".
Probably because there may be an upper limit on the size of an individual celestial object (and thus on how many particles it can consist of) - for it to be anything other than a black hole, anyway. In the future, the Universe will entirely consist of black holes, whose number will be much smaller.
I don't know what limits there are on the size of galaxies, though I suspect it share some characteristics with that of stars.
For star formation, however, the tension is between the outward flow of matter and simple photonic pressure on interstellar gas, competing against the inward pull of gravity.
That is: stars form as large "dust" clouds (mostly hydrogen atoms, obviously), collapse. Once those reach a critical mass, fusion initiates within the stellar core. The rate of fusion is moderated by the pull of gravity, such that larger stars, fighting more inward mass, burn far hotter (and faster, and live comparatively short lives: a few tens of millions of years for the very largest, as compared with ~10 billion for the Sun, and potentially trillions for brown dwarfs which eke out their fuel slowly).
In a curious bit of physical synchronicity, the energy density of the Sun's core (the part which is actively generating energy), in terms of watts/kg, is roughly equivalent to that of mammalian metabolism. It's just that there's a whole lot more mass to the Sun's core than there are mammals, and of course, we're comparing nuclear reactions with chemical ones (the Krebs Cycle).
Back to stars: as they ignite, they start blowing the dust that's forming them away, and so limit their maximum growth potential. The least massive stars (brown dwarfs) are roughly 10x the mass of Jupiter, or about 1/100th the mass of our Sun, the most massive stars are roughly 100x the mass of the Sun, giving a total effective range of roughly 1:10,000. The upper bound, called the Eddington Mass Limit, is about 120 solar masses, and is based on total luminosity which translates to outward pressure exerted by the star against the stellar medium surrounding it:
I don't know what the dynamics governing galaxy growth are, though a few ideas come to mind. Apparently the most massive galaxies are about 100x the size of the Milky Way (so we're at roughly similar ends of the scale for both stars and galaxies in that regard) in the Physics StackExchange post below. The discussion there does mention luminosity and pressure, though there's also some disagreement over just what constitutes a galaxy, and where to draw borders.
This will sound stupid... but as we find out that the universe is bigger and bigger and there are more clusters, galaxies, stars, and planets then we have imagined before (Laniakea have 100,000–150,000 galaxies and the Milky Way _alone_ have 100–400 billion stars)
so does that increase or lower the chance that there is _any_ kind of life outside there? Maybe not carbon-based life but any kind. Next question would be I guess that what is "life"
Realize that if the cosmological constant has the nonzero value that appears to be the case (in the lambda-CDM model), then only about 6% of the galaxies we see are still reachable. The rest will be carried away by accelerating expansion so quickly that a photon emitted from us right now (or any slower than light spaceship) will never reach them.
Of course more stars increases the chance of life out there, but without a good handle on the chance of life arising around a random star, we cannot set any lower bound on the probability that life is out there on the stars we see.
Wild, I've def heard of some reasons how the Fermi paradox could be resolved, but I missed this explanation. A quick headline scan of the wiki article also doesn't mention it. [1]
You'd think that 94% of the observable universe not being reachable would get more of a mention. Granted, we can still look for artifacts such as radio signals or something similar, but it does seem to cut out why a type 3 civ hasn't shown up at our door.
That's because it doesn't bear on the Fermi paradox at all. The Fermi paradox is about how information from/about aliens could have reached us in the past, whereas GP's comment is about how information from/about us could reach aliens in the future. Very different questions. Put another way, the mere fact that we can see the 94% of future-unreachable galaxies means they're a problem for Fermi, regardless of whether we can signal to them.
As one sci-fi writer said, for all the epic space operas ever written and all huge fictional empires ever imagined, they all would fit into just one little border of our Orion Arm (or Local Arm) of Milky Way. There's more than enough of everything.
Wait, what? SG:U is about multiple galaxies. Pretty sure many operas also use at least that setting. That writer may have talked about pop-scifi where “something something galaxy” is a best spot for a “wow”, given that on average people don’t know how space is structured beyond that.
I believe the comment is more about the practical reality of it - I can say that I have a story that takes place across the whole universe, but if the scenes only take place in a handful of planetary systems, even if I say they're in different galaxies, it could all fit in a tiny fraction of a single galaxy.
My favorite Fermi-friendly space opera setting would involve panspermia in the Sun's natal cluster. This would suppose origin of life in that cluster (not necessarily in our solar system), very soon after star formation, followed by seeding of the other star systems there. This would end up with about 10,000 lifebearing star systems, spread in roughly a half circle around the center of the Milky Way, with our solar system somewhere on that arc.
They meant that there's never any need to call it "multiple galaxies", except for wow effect, it would always fit into Local Arm, no matter how big the imagination went.
And more specifically the Drake equation (a subsection of the wikipedia article).
I personally think anyone's "answer" to the paradox just reveals their personal opinion/ what they want to believe, rather than any meaningful result from data.
This question has been (very unsatisfyingly) answered, or at least resolved:
> When the model is recast to represent realistic distributions of uncertainty, we find a substantial probability of there being no other intelligent life in our observable universe, and thus that there should be little surprise when we fail to detect any signs of it.
This isn't a satisfying resolution at all, it's akin to someone saying "I disagree with the value you used for X, it should be __ instead" - which is basically what I said: it reveals their personal opinion/ what they want to believe.
The article says they "incorporat[e] models of chemical and genetic transitions on paths to the origin of life" -- I'm not an expert but that sounds like the territory of some very unsettled science.
I don't think there's been a significant increase in the estimated # of galaxies lately. Identifying clusters is really about identifying areas of higher density that form some cohesive unit, rather than an increase in the actual count of galaxies.
There is other live with almost 100% certainty in the universe. The number of galaxies, stars and planets across the whole universe is just too large for this not to be true.
The thought that humans might be the only life in the universe to me seems like the 21st century equivalent of believing earth is the center of the universe.
>The thought that humans might be the only life in the universe to me seems like the 21st century equivalent of believing earth is the center of the universe.
Or it's an acknowledgment of the posterior data that has arisen over the past 30 years.
Every human has a camera 24/7 now and no one has documented visitors. Countless new missions and sensor arrays have found no evidence of life anywhere.
That doesn't prove no life, but it does make it more likely that the Drake equation is based on assumptions that are fundamentally flawed. Otherwise the Fermi paradox wouldn't still be a paradox.
Maybe it's all a simulation. Maybe it's something from a completely different paradigm. Who knows. But insisting they're out there as more decades pass with none found...that may be the real insistence that the sun revolves around the earth.
That there is no complicated life in Sol system besides on earth, or even within 50 light years of Sol system, and that there is complicated life in other parts of the universe are easily mutually compatible facts. Considering our search exhaustive at this point is selling the size of the universe short. We'll likely never interact with extra terrestrials, but it's silly to assume they're not out there.
The jist of what he says, is that there's very much weird stuff seen in the sky, like the McMinnville photos [1], but there's nobody as yet landing a craft on the White House lawn and posing for the cameras.
He puts forward a model for this kind of scenario, it's worth a listen, that any visitors would quite rightly be far in advance of the societies we currently live in, and may only show themselves fleetingly so we gain an acceptance of their presence.
The "weird stuff" is always distant, blurry, shot under terrible conditions, etc. Yet when a research team, or random passer-by snaps a photo of some never-before-seen, or thought-extinct creature, there's no difficulty in getting a quality image, either on the initial sighting or shortly afterward. It's only the "aliens" that are so problematic.
As for the idea that "they" are doing it deliberately (and perfectly)... it reminds me of the TIGHAR folks and Amelia Earhart. TIGHAR knows that Earhart crash-landed on Nikumaroro (Gardner Island), so every piece of information they see is interpreted through the lens of how it fits with that interpretation. But they have no root basis for the conclusion, just that they really want to believe it.
When faced with the question, "Why are pictures of possibly alien UFOs blurry?" two (of many) possible answers are "because if they're not low-quality we can tell they're not aliens" and "because the aliens are carefully arranging circumstances so that pictures of them are always low-quality" I know which one I'm putting my money on.
The problem is that "Technology allowing an advanced civilization to travel to Earth, enter the atmosphere, leave, etc." is significantly more complex than "Technology that would allow them to be completely undetectable to us, and also not crash into the planet"
"Only detectable by people with bad gear" is just not a technological state that makes sense in this context.
There is A LOT of stuff recording what's going on in the sky at all times. A lot of stuff that could give us detailed and high resolution images and other readings. Some of it is actively beholden to various governments so I guess you could argue it's being kept from us there - but are all of these governments going to be in lockstep on this issue? And even more aren't - are scientists going to all just keep quiet on this?
We've had all these declassified videos released recently, and they're some of the most obvious not-extraterrestrial-visitors ever. The one recorded on an aircraft carrier through nightvision with the flying triangles? Night vision goggles have triangular apertures. Bokeh takes the shape of the lens aperture - so bokeh lights become triangles. The blinking in and out of existence? Same timing pattern as a commercial jet.
The pill video from the jets? Parallax makes stationary things look like they move fast. The pill only ever looks to rotate/change direction when the actual recording device in it's housing also does. It's all stabilized so it's not readily apparent unless you know to look for it, but it becomes obvious when you do. What is the object itself? It could be a mylar balloon, it could be an IR hot spot from the sun reflecting off the water. Could be other things. What we don't have any reason to believe is that it is some sort of advanced craft with physics-defying maneuverability.
I fully believe that there is intelligent life out there. Probably in our galaxy, but near certainty in the universe. I also believe that the chances we have had intelligent visitors from another place is the barest fraction of a fraction of a percent.
Have a look at the Grabby Aliens model [1] when essentially says:
1. We are likely amongst the earliest of advanced space-faring civilisations that have ever exists, which is why we haven't established evidence of other life,
2. There are 'quiet' civilisations and 'loud' civilisations. We will never see evidence of 'quiet' civilisations, and the other 'loud' civilisations haven't expanded sufficiently to be observable at this point in time.
3. Assuming we don't die out ourselves and are therefore a 'quiet' civilisation, we should encounter the other 'loud' civilisations sometime in the next hundred million years or so :-)
Not sure I buy the "we are special/early" explanation.
However I don't think it makes sense for any civilization to be 'loud'. Just seems naive to blunder about and risk your civilization. However monitoring new civilizations for intelligence, fairness, open mindedness, lack of religions that justify killing outside their religion or species, treating the less fortunate of their/other species well and the like. Then once they hit some developmental milestones for compatible civilizations you introduce yourselves. Possible milestones include practical fusion, returning your ecosystem to baseline, practical anti-matter production/use, making a blackhole, traveling to the nearest star that you don't orbit, quantum computing at scale, etc.
Might well be something on the moon, well stealthed, a few meters down, with receivers capable of decryption RF traffic, and sensors to see how quickly we are poisoning ourselves.
If you think about it, if you were an alien watching earth, would you want to meet us? Or terminate us, at least the humans, and wait for something else intelligent to appear.
Space is much bigger than you are accounting for and the speed of light much slower. If the nearest spacefaring civilization is in the next galaxy over, we will never meet them. It actually seems rather unlikely any spacecraft could ever reach us unless they evolved right in our backyard, within a few dozen light years.
But to be fair, it’s not like we’ve been able to look very many places. We’ve checked a few of the planets in our own solar system and it could be plausible to detect a civilization within a few light years by radio wave if we were very lucky.
It’s also extremely hostile to anything non-trivial like biology or electronics. We all have that cool space-faring ideas in mind from scifi, but reality is more like swimming in a tiny boat through the storms of Pacific Ocean and it’s acid.
That perspective is a somewhat human-centric one. There’s nothing stopping some aliens from having lifespans in the thousands or even millions of years. For those cultures, a 300 year trip is nothing!
Furthermore, Andromeda galaxy is on a collision course with the Milky Way. If there’s an intelligent alien culture there, they might get here just by waiting.
Well we reproduce so it’s really the same difference. The huge limiting factor for getting between stars seems to be the rocket equation. You have to invent magic propulsion to cross the galaxy.
> Every human has a camera 24/7 now and no one has documented visitors.
You are being willfully obtuse. There have been thousands of documented sightings over the past 80 years. Audiovisual recordings abound, not infrequently matched with radar or other secondary corroborating evidence.
The typical response to this is:
1. “They are faked.”
2. “That doesn’t mean it’s aliens.”
3. “It’s a secret government program.”
Fine. Nevertheless some percentage of documented events cannot be explained. There is a non-zero chance that they are caused by things that were not made by humans. They deserve to be scientifically investigated in good faith, without the arrogant dismissiveness that is so frequently encountered.
A much bigger elephant in the room is the fact that nearly all mass of the universe is made of dark matter and we have no clue what it is.
It seems plausible to me that by the time a civilization can quickly travel to other stars, it becomes so different that it doesn't need to interact or even be visible to advanced monkeys on a distant planet, just like we aren't really striving to talk to exotic monkeys on isolated islands. And the only reason those exotic monkeys and birds haven't become our food, like cows or pigs, is that there is very little protein on their bones (speaking bluntly).
We also wonder why we don't see alien activity in radio spectrum, while at the same time we use encryption to make radio wave communication indistinguishable from noise. More advanced civilization might have learnt that not getting noticed is vital to survival, so they scramble all signals. That background microwave noise might be those signals scrambled.
Talking of the extreme case of life being unique to earth seems unnecessary; there can't be many people outside of some fundamentalist niches that hold that view.
More generally on the subject considered seriously, without taking into account the various factors involved in predicting the probability of life it is unwise to talk of certainty and scoff at sceptics of its abundance.
There is also an important distinction to be made between life in its simplest form and at its apex; it is the latter that perhaps most people think of when looking upwards in wonder, and there is no reason to think that the distribution of intelligent life is such that we have good chances of contact and interaction, however we may wish it to be so.
> There is other live with almost 100% certainty in the universe. The number of galaxies, stars and planets across the whole universe is just too large for this not to be true.
So this argument gets repeated slot (because people like repeating things they hear) but it's completely fallacious.
Yes, the amount of planets is astronomically large. But it might be that the probability that life appears on a planet is astronomically small. If there are 10^50 planets in the universe, but the probability that life appears on a planet is 10^(-60), then we're probably the lucky one.
In other words, we don't know, but please stop repeating garbage.
The universe is unfathomably big. Some hazy but AFAIU relatively accurate napkin math suggests that there are more stars in the universe than there are grains of sand on all of Earth's beaches. But at the same time, there are more molecules in ten drops of water than there are stars in the universe.
It seems scientifically implausible that we are alone. I base this on a few things:
Life started on Earth almost as soon as the surface was cool enough to support it. The surface seems to have been stable enough for life by 3.8 billion years ago, and we have some weaker evidence of life at 3.7 and stronger at 3.5. At any rate, based on what we can observe, life began relatively early and so it seems that as soon as the basic building blocks and preconditions are present, life evolves.
We now know that exoplanets are extremely common. Based on observations we can estimate that about 40% of stars have planets, but that’s just what we’ve been able to observe.
There are a lot of stars in our galaxy, 100-400 billion.
And a lot of galaxies in the observable universe, 200 billion to 2 trillion.
And that’s just the observable universe based on our local light cone. For all we know, there could be an infinite number of galaxies.
So we have n=1 where life started right away, and perhaps 10^25 planets in the observable universe. That’s a lot of rolls of the dice!
Hence the need for a proposed great filter that explains why we don’t get a visitor ever other week. Complex multicellular life seems like a possibility, that took quite awhile, a few billion years before the Cambrian explosion. Complex intelligence also took awhile, resulting in only us after 3.5 billion years of life. And yeah, given that we haven’t been around all that long and seem well on our way to destroying ourselves, seems like complex society could be a great filter too. But space is vast, EM signals attenuate quickly and the speed of light is a harsh mistress. They are probably out there, but we’ll probably never meet them.
Uh, we don’t necessarily need a great filter to not be constantly visited - we just need a lack of ‘cheat codes’ (like warp drives, wormholes, dirt cheap energy from magical fusion or zero point or whatever), combined with relatively short lived complex civilizations.
If no one can afford the trip (due to what we currently know of physics), or survive as a complex civilization long enough (100k+ years), then… you see what you see right now.
If you're talking about sending live people, absolutely
If you're talking about sending alien drones, the light mass and lack of having to keep them alive makes energy requirements a lot lower, but they'd probably just be scouting us (if not trying to kill us) so we wouldn't be able to detect them
Considering no human object has yet to leave the solar system (meaningfully), and we’ve nearly wiped ourselves out several times just in recent memory - that’s still in the realm of pure fantasy.
There is no evidence yet that anything we can construct (or a near peer) could make it to another system intact enough to know it had arrived, let alone DO anything regardless of the form any intelligence takes or how it is packaged.
Hell, as a species we still struggle to land probes on mars and Venus. And they don’t have to do anything but send data back.
Getting a toehold on a random solar system, or even arriving and taking pictures and sending them back is so many orders of magnitudes harder to do based on what we know now it’s essentially impossible. Even if we had a ‘fast forward’ button.
Hopefully we’ll find something out that we’re currently missing, but as of yet we have no reason to believe it exists.
Not sure what "meaningfully" is supposed to mean here, but both Voyager probes have gone passed the heliopause and are outside our solar system from that perspective.
"However, if we define our solar system as the Sun and everything that primarily orbits the Sun, Voyager 1 will remain within the confines of the solar system until it emerges from the Oort cloud in another 14,000 to 28,000 years."
"The twin Voyagers are the only man-made objects to have entered interstellar space. However, while they have left the heliosphere, they have not yet left the boundary of the Solar System which is considered to be the outer edge of the Oort Cloud."
It's still in the area of things that primarily orbit the sun, even if it is no longer in the 'atmosphere' or 'shade' of the Sun (aka the heliopause, which is what was being used for PR purposes).
And it's nowhere near anything which isn't orbiting the sun, and nowhere near 'not being in' the area of things orbiting the sun.
So meaningfully, it's still in the solar system, and will be for a very long time. It's just out of the nice part.
Distance wise, Voyager 1 (the furthest) is ~ 22 light hours away, or .02% of a light year - after travelling for 45 years. Proxima Centauri, the closest known star to us is 4.25 light years away.
It would take ~ 73,000 years at Voyagers blistering pace (38,000 mph) to reach it, and there is essentially zero chance we could keep contact with it or it would be functional even 1/10th of that time - it's RTG is already nearly dead, and with a ~ 87 year half life, it would be a miracle if it even lasted another 50-100 years.
Voyager was meant to take pictures of objects in our celestial sphere, if instead we were in a race to, for instance, yeet our stuff faster than the soviets towards Proxima Centauri, everything would have been different.
Care to do the napkin math on what it would take energy wise for anything to make it from here to Proxima Centauri in 50 years or less? (Approx. rounded up time of the entire Cold War)
Hint: even with instant construction, even nutty ideas like Project Orion would be incapable of doing it, let alone anything else. We’re talking > 10% the speed of light for the entire trip.
You just proposed a great filter, short lived civilizations.
If civilizations lasted for billions of years or their AGIs did the same, we’d have a lot higher chance of them expanding to fill the galaxy and converting the surface of all 8 planets and major asteroids into AGI probes and compute.
That’s not what I’d consider a great filter in the usual usage. We’ve only had ~10k years of recorded history. If we can’t make a meaningful dent somewhere outside the solar system in another 10x that amount of time, I doubt we (or anyone) ever would.
A civilization doesn’t have to survive a billion years (do you know how long that actually is?) to not be ‘short lived’.
I would define short lived as the difference between dying out in a local star cluster or continuing to expand till the heat death of the universe. A long-lived and expansionary civilization will eventually reach us, even if it takes 1k years to hop from star to star. A short lived civilization will never reach us.
None of the situations you’re giving are based entirely off longevity - they use longevity as a factor of another equation.
A billion year old civilization that isn’t expansionary will never reach us either.
Or one that doesn’t want to spend the energy ($$$) if other cheap energy forms we’ve speculated aren’t possible or as inexpensive/portable as would be needed.
They could just as easily be happy being billion year old zen masters, and we’d never know - even if they had warp drives.
They’d still exist though, and if we ever wanted to find them I guess we’d be able to do so. But we’d never know about them proactively.
Something like a fleet of von Neumann probes could expand across the entirety of the galaxy in a million years or so, and wouldn't care if the original civilization had long since flamed out. Which is long time by our standards, but not too long on the cosmological scale. In theory there should have been lots of habitable places where life could have arisen in our galaxy long enough in the past that the whole place could be "colonized" in this manner.
Of course, there could be plenty of these floating around our solar system and we wouldn't know. They could be quite small and the solar system is quite big, and most of the proposed use cases for a civilization wanting to do this would not require it be in constant contact, so they might not even be broadcasting on anything resembling a frequent basis.
But in general there are a lot of theoretical technosignatures that we think we should be able to see if there was technological advanced life in the galaxy. (Should be able to see in that it is possible with our current technology - not that we would conclusively have seen it by this point.)
It’s a nice idea in theory, but we’ve seen no evidence Von Neumann probes are even possible, or that any civilization would consider them worth investing in.
If you do the math, unless there are the aforementioned ‘cheat codes’, they frankly just don’t pencil out as worthwhile. No FTL/subspace? No ‘infinite cheap energy’ hack? No ‘infinite self replicating yet controllable builder of anything’ molecule?
No way to propagate, no way to energize, and no way to communicate at any real scale over the distances involved. Even gigawatt power, high efficiency, high precision aimed lasers aren’t going to have much luck at light year distances, and nothing is going to be useful for two way communication.
It’s easy to speculate of course, but like ‘grey goo’ it runs up against real issues with thermodynamics and physics if we stop and think about it much.
Worth investigating options of course, or talking about, but if physics is what it seems to be so far, that would perfectly explain the lack of us seeing them - they’re not useful/practical/worth the expense for anyone.
Worthwhile to invest in I think is the bigger question - from a practical 'can we build a self replicating probe fleet that would eventually cover the galaxy', there's at least evidence that it's possible in the next hundred years or so.
In general I do think it makes sense to not just contemplate interstellar visitors as living things making the trek or biological civilizations expanding, but there's a wide variety of artificial ~things~ that could end up in our solar system for whatever reason.
Uh, that isn't evidence? That's speculation on potential future technical advances.
The only things we see self replicate are currently biological systems, and they can only do it under very specific circumstances and usually with a LOT of external help.
Circumstances which do not exist in space, let alone under the variety of environments on just the handful of planets we see in our solar system - except one, of course.
It's a very hard problem, and it isn't clear there is an actual answer that is economic to stick on the end of a rocket, even just to get to the moon. Something that survives 10k+ year journeys to unknown environments, and then does something useful? Even less clear.
Gets there AND then has the level of success necessary to transmit any sort of signal, or propagate itself further? Even less so.
Why we would do it, is also unclear.
Hopefully we'll figure out something that makes it less fantastical at some point - all the things that make it realistic would also help us in many other ways too!
We've got a pretty good track record in predicting near-ish-future scientific/technological advances, which is what we would need for self replicating machines. To be clear, I'm not talking nanobots or similar - much more macro sized stuff. All the constituent pieces to make a self replicating mining robot or whatever are there today, and we already automate a lot of the processes required. There are some important gaps to fill, for sure, but none that we have any real reason to believe are insurmountable.
We're in agreement that the 'why' is less clear, at least for probes exploring the galaxy. But there are some very clear reasons why this sort of tech in general is useful - mining the asteroid belt, building reflectors to better harness the energy of the sun, building all sorts of other infrastructure in space without having to use a rocket to get it there. At that point once we have the tech and are doing it - and I would be shocked if the human race is still around in 500 years and NOT doing that sort of thing - it's relatively cheap to kick off a bunch of probes doing similar things.
I'm still not sure if it's worth it in that scenario, but it's conceivable that it could be. And that puts us again on the question of why we don't see it. We think there should be a lot of intelligent life out there. There's a lot of very important 'if's in all of this, but if we can think of it and and conceive of some potential reasons, and if other intelligent life has these capabilities that we believe will be possible, and if it becomes as resource/energy/time efficient to do as it should be, then it seems like someone, somewhere, should have been able to convince their government or corporation or whatever to do it, even if the results aren't necessarily going to be super apparent. The Pioneer plaque is obviously much cheaper, but we knew beforehand that the utility there is basically 0%.
Like I said, I'm not necessarily arguing that these probes are out there. I'm guessing the answer is more likely "There's no compelling reason to colonize or even explore large swathes of the galaxy" and concerns around interstellar travel are on such large timescales that civilizations capable of interstellar travel would only care about their nearest neighbors. Maybe that changes as star formation spins down and the galaxy starts to slowly go dark and your local galactic resources are less and less abundant. I'm just saying that there are technosignatures that would indicate the presence of other intelligent life in the galaxy that have nothing to do with biological beings visiting us, and we would expect that some of these are possible for us to see now, if they're out there.
All it takes is for a Magnetar to have a hiccup and it could sterilize an entire galaxy.
When we take numbers and probabilities in consideration it's good to also note how many hostile to life events can occur on a cosmic scale. You have supernovas, gamma ray bursts, black holes, neutron stars, magnetars, solar flares and coronal mass ejections, and a host of other shit we don’t even now about that could destroy life at any stage.
> All it takes is for a Magnetar to have a hiccup and it could sterilize an entire galaxy.
There are tens of millions of magnetars in the milky way and we can and do observe their "hiccups" - we've traded a multitude of GRBs back to stars we believe to be magnetars.
They do not have anywhere near enough energy to sterilize an entire galaxy.
as soon as the basic building blocks and preconditions are present, life evolves
If not for that one mutation under specific conditions and abundance of easily freeable oxygen, we’d still be goo in mud today. We were for 1.4 billion years until GOE happened.
It doesn’t mean that it cannot happen elsewhere. But there’s no clear linear route from complex acids to democracy. And maybe complex enough life requires a set of very special catastrophes. We can’t write off that we managed to evolve, but we can’t write off the exact procedure either.
The more galaxies we can see, the more lack of evidence we have for any large scale changes to the universe by any intelligence. Many people take this as an indication that there is no other intelligent life or life of any kind in our observable universe. Also see: grabby aliens.
There's a part of me that thinks that life represents a key property of the universe, one that we may see accelerate drastically in our lifetimes. All around the universe we see entropy (in a broad sense) - the turning of order to disorder, the fundamental march toward the eventual heat death of the universe. But life is the one thing we're aware of that actually trends toward increasing order - starting with unicellular organisms, then the cambrian explosion, then the evolution of humans, then our highly advanced and organized societies... and now we're on the cusp of inventing AI. An invention that, as Kurzweil puts it, could eventually turn all the matter into the universe into a giant computer of sorts and use it to simulate another universe. I don't know, if you ask me, this represents some sort of fundamental force, or constant, or thing, that we haven't quite gotten to the bottom of yet. Some property of the universe that simply trends toward increasing complexity under specific conditions.
For the neverending stream of talk about VR this, metaverse that, and WebGPU there, there should really be a KISS 3D format for the web so we can view things like this properly. Like Markdown simple. No shaders or animation or anything like that. Default lighting only.
It feels sad to look at a 2D image of the most 3D of all things.
How about VRML or its successor X3D? They support fanciness, but you don't have to use it any more than you have to use every random feature in Markdown.
"The Department of Physics at the University of Maryland, Baltimore County discovered that a large mass of gas is hurtling through the cluster at a speed of 750 km/s (466 miles/second). The mass is billions of solar masses, approximately 3 million light-years in diameter and is the largest of its kind discovered as of June 2006."
We need Faster Than Light (FTL) travel otherwise we’re stuck here on Earth. I believe that there are other beings out there, but the vast distances prevent contact. If they haven’t discovered exotic means of travel like wormholes, hyperspace, warp drives, or something else, then we’re doomed to remain separated :-(
We’re not doomed and we don’t need to be separate. We just need to be patient. We must be willing to send generations of humans on thousand year journeys.
Physics has all but ruled out faster than light travel for squishy beings like humans, or for that matter even sensitive electronics.
The equations that allow for wormholes or Alcubierre drives don't mean it's possible for living beings or working electronics to actually successfully make a trip through such extreme and unlikely phenomena.
It's a bit like saying you'll slingshot around a black hole close to its event horizon to gain enormous speed: you could do that, but tidal forces will rip you apart in the process. Except wormholes and other such spacetime anomalies are worse.
Tidal forces are highly dependent on the mass of the black hole. The more massive, the less tidal forces you have to contend with.
The bigger problem is finding such a black hole that doesn't have a very unfriendly to life and electronics accretion disk.
I've seen some arguments that alcubierre drives could allow for safe transportation with materials science advancements that we believe to be possible. Safe for the people traveling, at any rate. Not so safe for your destination and whatever else is in a large cone in front of your ship.
I've not seen any convincing arguments that would allow for anyone to safely traverse a worm hole, however.
Right, I should have qualified the black hole mass. But it doesn’t affect the point, which is that just because equations tell us that some favorable path through spacetime is physically possible, doesn’t mean we could survive the trip.
As for Alcubierre drives, they’re interesting as a problem in highly speculative physics. But when people start taking as if we might actually build one, they lose me. I guess perhaps it’s kind of a fantasy game, like talking about gods, but if you’re not a believer or interested in playing the game, it just seems pointless. They’re not real and they’re extremely unlikely to ever be real.
Start with an analogy: We've never seen a car before but find one, learn how to drive it, and are amazed, and ask "How does this amazing thing work?". We study the rubber in the tires, the disk brakes, the air conditioning, the universal joints, differential, the transmission, the pistons.
Then we see the box that has the computer for controlling the fuel injection and ignition and start to take it apart to see how it works when one of us says:
"Stop. In broad terms, I can tell you how it works: It does what it needs to do so that the car can work. But by now we have gone so deep into how this car works that it is time to ask
What is the purpose of this car?"
The universe as it seems from current astronomy, ..., is one huge and intricate construction. Sorry, but tough to believe that all of this has no purpose.
Ah, two possibilities:
(1) We really are the center of the universe and the only life.
There is a lot less to the universe than what seems from current astronomy. In particular, objects we can never reach due to the speed of light limit are just fake, something like a painted screen.
(2) We have not found it yet, but there is a way to violate the speed of light. The whole universe is ours for the taking once we see how to exceed the speed of light. There is a game: For the laws of physics, how long will it take for life to develop to understand these laws and, in particular, how to exceed the speed of light?
For either of (1) or (2), maybe we should start a new subject, super cosmology, that assumes that the universe has a purpose. We look for that purpose and, for each discovery we make, e.g., dark matter, quantum mechanics, black holes, quasars, gravitational waves, ..., ask what its role is in the purpose of the universe.
122 comments
[ 2.3 ms ] story [ 203 ms ] threadhttps://www.wolframalpha.com/input?i=log2%2810%5E80%29
https://www.thoughtco.com/number-of-atoms-in-the-universe-60...
Plus there's that scene from Stargate Universe:
- Are those stars?
- No, those are galaxies.
I wonder how long before we can
The problem is that at such timescales, the CMB will have shifted sooooooooo much that there’s nothing they will be able to deduce, all light has redshifted to absurd scales, and worst of all, everything will be so far away that light will never reach the galaxy.
If their physics is correct, they will figure it out. We did because we verified that expansion is accelerating even though our physics are incomplete. Until the late 90s, physicists accepted a cosmological constant of 0, which meant no acceleration. Turns out that that was wrong.
It may be possible that they figure it out via Quantum Mechanics because it seems that acceleration of the universe is related to the energy density of a vacuum / empty space. The problem is that they won't be able to empirically verify that I think.
[1] https://en.wikipedia.org/wiki/Intergalactic_star
For star formation, however, the tension is between the outward flow of matter and simple photonic pressure on interstellar gas, competing against the inward pull of gravity.
That is: stars form as large "dust" clouds (mostly hydrogen atoms, obviously), collapse. Once those reach a critical mass, fusion initiates within the stellar core. The rate of fusion is moderated by the pull of gravity, such that larger stars, fighting more inward mass, burn far hotter (and faster, and live comparatively short lives: a few tens of millions of years for the very largest, as compared with ~10 billion for the Sun, and potentially trillions for brown dwarfs which eke out their fuel slowly).
In a curious bit of physical synchronicity, the energy density of the Sun's core (the part which is actively generating energy), in terms of watts/kg, is roughly equivalent to that of mammalian metabolism. It's just that there's a whole lot more mass to the Sun's core than there are mammals, and of course, we're comparing nuclear reactions with chemical ones (the Krebs Cycle).
Back to stars: as they ignite, they start blowing the dust that's forming them away, and so limit their maximum growth potential. The least massive stars (brown dwarfs) are roughly 10x the mass of Jupiter, or about 1/100th the mass of our Sun, the most massive stars are roughly 100x the mass of the Sun, giving a total effective range of roughly 1:10,000. The upper bound, called the Eddington Mass Limit, is about 120 solar masses, and is based on total luminosity which translates to outward pressure exerted by the star against the stellar medium surrounding it:
<https://en.wikipedia.org/wiki/Eddington_luminosity>
I don't know what the dynamics governing galaxy growth are, though a few ideas come to mind. Apparently the most massive galaxies are about 100x the size of the Milky Way (so we're at roughly similar ends of the scale for both stars and galaxies in that regard) in the Physics StackExchange post below. The discussion there does mention luminosity and pressure, though there's also some disagreement over just what constitutes a galaxy, and where to draw borders.
<https://physics.stackexchange.com/questions/172953/what-is-t...>
so does that increase or lower the chance that there is _any_ kind of life outside there? Maybe not carbon-based life but any kind. Next question would be I guess that what is "life"
Fascinating stuff nonetheless
Of course more stars increases the chance of life out there, but without a good handle on the chance of life arising around a random star, we cannot set any lower bound on the probability that life is out there on the stars we see.
You'd think that 94% of the observable universe not being reachable would get more of a mention. Granted, we can still look for artifacts such as radio signals or something similar, but it does seem to cut out why a type 3 civ hasn't shown up at our door.
[1] https://en.wikipedia.org/wiki/Fermi_paradox
And more specifically the Drake equation (a subsection of the wikipedia article).
I personally think anyone's "answer" to the paradox just reveals their personal opinion/ what they want to believe, rather than any meaningful result from data.
> When the model is recast to represent realistic distributions of uncertainty, we find a substantial probability of there being no other intelligent life in our observable universe, and thus that there should be little surprise when we fail to detect any signs of it.
https://arxiv.org/abs/1806.02404
SSC has an article on the paper as well
https://slatestarcodex.com/2018/07/03/ssc-journal-club-disso...
The article says they "incorporat[e] models of chemical and genetic transitions on paths to the origin of life" -- I'm not an expert but that sounds like the territory of some very unsettled science.
The thought that humans might be the only life in the universe to me seems like the 21st century equivalent of believing earth is the center of the universe.
Or it's an acknowledgment of the posterior data that has arisen over the past 30 years.
Every human has a camera 24/7 now and no one has documented visitors. Countless new missions and sensor arrays have found no evidence of life anywhere.
That doesn't prove no life, but it does make it more likely that the Drake equation is based on assumptions that are fundamentally flawed. Otherwise the Fermi paradox wouldn't still be a paradox.
Maybe it's all a simulation. Maybe it's something from a completely different paradigm. Who knows. But insisting they're out there as more decades pass with none found...that may be the real insistence that the sun revolves around the earth.
Take a few minutes to listen to Prof. Robin Hanson talk on this very thing.
https://youtu.be/cQq2pKNDgIs
The jist of what he says, is that there's very much weird stuff seen in the sky, like the McMinnville photos [1], but there's nobody as yet landing a craft on the White House lawn and posing for the cameras.
He puts forward a model for this kind of scenario, it's worth a listen, that any visitors would quite rightly be far in advance of the societies we currently live in, and may only show themselves fleetingly so we gain an acceptance of their presence.
[1] https://en.m.wikipedia.org/wiki/McMinnville_UFO_photographs
The "weird stuff" is always distant, blurry, shot under terrible conditions, etc. Yet when a research team, or random passer-by snaps a photo of some never-before-seen, or thought-extinct creature, there's no difficulty in getting a quality image, either on the initial sighting or shortly afterward. It's only the "aliens" that are so problematic.
As for the idea that "they" are doing it deliberately (and perfectly)... it reminds me of the TIGHAR folks and Amelia Earhart. TIGHAR knows that Earhart crash-landed on Nikumaroro (Gardner Island), so every piece of information they see is interpreted through the lens of how it fits with that interpretation. But they have no root basis for the conclusion, just that they really want to believe it.
When faced with the question, "Why are pictures of possibly alien UFOs blurry?" two (of many) possible answers are "because if they're not low-quality we can tell they're not aliens" and "because the aliens are carefully arranging circumstances so that pictures of them are always low-quality" I know which one I'm putting my money on.
"Only detectable by people with bad gear" is just not a technological state that makes sense in this context.
There is A LOT of stuff recording what's going on in the sky at all times. A lot of stuff that could give us detailed and high resolution images and other readings. Some of it is actively beholden to various governments so I guess you could argue it's being kept from us there - but are all of these governments going to be in lockstep on this issue? And even more aren't - are scientists going to all just keep quiet on this?
We've had all these declassified videos released recently, and they're some of the most obvious not-extraterrestrial-visitors ever. The one recorded on an aircraft carrier through nightvision with the flying triangles? Night vision goggles have triangular apertures. Bokeh takes the shape of the lens aperture - so bokeh lights become triangles. The blinking in and out of existence? Same timing pattern as a commercial jet.
The pill video from the jets? Parallax makes stationary things look like they move fast. The pill only ever looks to rotate/change direction when the actual recording device in it's housing also does. It's all stabilized so it's not readily apparent unless you know to look for it, but it becomes obvious when you do. What is the object itself? It could be a mylar balloon, it could be an IR hot spot from the sun reflecting off the water. Could be other things. What we don't have any reason to believe is that it is some sort of advanced craft with physics-defying maneuverability.
I fully believe that there is intelligent life out there. Probably in our galaxy, but near certainty in the universe. I also believe that the chances we have had intelligent visitors from another place is the barest fraction of a fraction of a percent.
1. We are likely amongst the earliest of advanced space-faring civilisations that have ever exists, which is why we haven't established evidence of other life,
2. There are 'quiet' civilisations and 'loud' civilisations. We will never see evidence of 'quiet' civilisations, and the other 'loud' civilisations haven't expanded sufficiently to be observable at this point in time.
3. Assuming we don't die out ourselves and are therefore a 'quiet' civilisation, we should encounter the other 'loud' civilisations sometime in the next hundred million years or so :-)
[1] https://grabbyaliens.com/
However I don't think it makes sense for any civilization to be 'loud'. Just seems naive to blunder about and risk your civilization. However monitoring new civilizations for intelligence, fairness, open mindedness, lack of religions that justify killing outside their religion or species, treating the less fortunate of their/other species well and the like. Then once they hit some developmental milestones for compatible civilizations you introduce yourselves. Possible milestones include practical fusion, returning your ecosystem to baseline, practical anti-matter production/use, making a blackhole, traveling to the nearest star that you don't orbit, quantum computing at scale, etc.
Might well be something on the moon, well stealthed, a few meters down, with receivers capable of decryption RF traffic, and sensors to see how quickly we are poisoning ourselves.
If you think about it, if you were an alien watching earth, would you want to meet us? Or terminate us, at least the humans, and wait for something else intelligent to appear.
https://physics.stackexchange.com/questions/245505/from-how-...
Furthermore, Andromeda galaxy is on a collision course with the Milky Way. If there’s an intelligent alien culture there, they might get here just by waiting.
You are being willfully obtuse. There have been thousands of documented sightings over the past 80 years. Audiovisual recordings abound, not infrequently matched with radar or other secondary corroborating evidence.
The typical response to this is:
1. “They are faked.”
2. “That doesn’t mean it’s aliens.”
3. “It’s a secret government program.”
Fine. Nevertheless some percentage of documented events cannot be explained. There is a non-zero chance that they are caused by things that were not made by humans. They deserve to be scientifically investigated in good faith, without the arrogant dismissiveness that is so frequently encountered.
Something mysterious is going on in our skies.
It seems plausible to me that by the time a civilization can quickly travel to other stars, it becomes so different that it doesn't need to interact or even be visible to advanced monkeys on a distant planet, just like we aren't really striving to talk to exotic monkeys on isolated islands. And the only reason those exotic monkeys and birds haven't become our food, like cows or pigs, is that there is very little protein on their bones (speaking bluntly).
We also wonder why we don't see alien activity in radio spectrum, while at the same time we use encryption to make radio wave communication indistinguishable from noise. More advanced civilization might have learnt that not getting noticed is vital to survival, so they scramble all signals. That background microwave noise might be those signals scrambled.
https://en.wikipedia.org/wiki/List_of_potentially_habitable_...
More generally on the subject considered seriously, without taking into account the various factors involved in predicting the probability of life it is unwise to talk of certainty and scoff at sceptics of its abundance.
There is also an important distinction to be made between life in its simplest form and at its apex; it is the latter that perhaps most people think of when looking upwards in wonder, and there is no reason to think that the distribution of intelligent life is such that we have good chances of contact and interaction, however we may wish it to be so.
So this argument gets repeated slot (because people like repeating things they hear) but it's completely fallacious.
Yes, the amount of planets is astronomically large. But it might be that the probability that life appears on a planet is astronomically small. If there are 10^50 planets in the universe, but the probability that life appears on a planet is 10^(-60), then we're probably the lucky one.
In other words, we don't know, but please stop repeating garbage.
https://www.npr.org/sections/krulwich/2012/09/17/161096233/w...
Life started on Earth almost as soon as the surface was cool enough to support it. The surface seems to have been stable enough for life by 3.8 billion years ago, and we have some weaker evidence of life at 3.7 and stronger at 3.5. At any rate, based on what we can observe, life began relatively early and so it seems that as soon as the basic building blocks and preconditions are present, life evolves.
We now know that exoplanets are extremely common. Based on observations we can estimate that about 40% of stars have planets, but that’s just what we’ve been able to observe.
There are a lot of stars in our galaxy, 100-400 billion.
And a lot of galaxies in the observable universe, 200 billion to 2 trillion.
And that’s just the observable universe based on our local light cone. For all we know, there could be an infinite number of galaxies.
So we have n=1 where life started right away, and perhaps 10^25 planets in the observable universe. That’s a lot of rolls of the dice!
Hence the need for a proposed great filter that explains why we don’t get a visitor ever other week. Complex multicellular life seems like a possibility, that took quite awhile, a few billion years before the Cambrian explosion. Complex intelligence also took awhile, resulting in only us after 3.5 billion years of life. And yeah, given that we haven’t been around all that long and seem well on our way to destroying ourselves, seems like complex society could be a great filter too. But space is vast, EM signals attenuate quickly and the speed of light is a harsh mistress. They are probably out there, but we’ll probably never meet them.
If no one can afford the trip (due to what we currently know of physics), or survive as a complex civilization long enough (100k+ years), then… you see what you see right now.
If you're talking about sending alien drones, the light mass and lack of having to keep them alive makes energy requirements a lot lower, but they'd probably just be scouting us (if not trying to kill us) so we wouldn't be able to detect them
There is no evidence yet that anything we can construct (or a near peer) could make it to another system intact enough to know it had arrived, let alone DO anything regardless of the form any intelligence takes or how it is packaged.
Hell, as a species we still struggle to land probes on mars and Venus. And they don’t have to do anything but send data back.
Getting a toehold on a random solar system, or even arriving and taking pictures and sending them back is so many orders of magnitudes harder to do based on what we know now it’s essentially impossible. Even if we had a ‘fast forward’ button.
Hopefully we’ll find something out that we’re currently missing, but as of yet we have no reason to believe it exists.
[https://solarsystem.nasa.gov/missions/voyager-1/in-depth/]
"The twin Voyagers are the only man-made objects to have entered interstellar space. However, while they have left the heliosphere, they have not yet left the boundary of the Solar System which is considered to be the outer edge of the Oort Cloud."
[https://en.wikipedia.org/wiki/Heliosphere#Heliopause] [https://www.nasa.gov/press-release/nasa-s-voyager-2-probe-en...]
It's still in the area of things that primarily orbit the sun, even if it is no longer in the 'atmosphere' or 'shade' of the Sun (aka the heliopause, which is what was being used for PR purposes).
And it's nowhere near anything which isn't orbiting the sun, and nowhere near 'not being in' the area of things orbiting the sun.
So meaningfully, it's still in the solar system, and will be for a very long time. It's just out of the nice part.
Distance wise, Voyager 1 (the furthest) is ~ 22 light hours away, or .02% of a light year - after travelling for 45 years. Proxima Centauri, the closest known star to us is 4.25 light years away.
It would take ~ 73,000 years at Voyagers blistering pace (38,000 mph) to reach it, and there is essentially zero chance we could keep contact with it or it would be functional even 1/10th of that time - it's RTG is already nearly dead, and with a ~ 87 year half life, it would be a miracle if it even lasted another 50-100 years.
Hint: even with instant construction, even nutty ideas like Project Orion would be incapable of doing it, let alone anything else. We’re talking > 10% the speed of light for the entire trip.
I'm just saying our space faring objects would be fundamentally a lot different
If civilizations lasted for billions of years or their AGIs did the same, we’d have a lot higher chance of them expanding to fill the galaxy and converting the surface of all 8 planets and major asteroids into AGI probes and compute.
A civilization doesn’t have to survive a billion years (do you know how long that actually is?) to not be ‘short lived’.
A billion year old civilization that isn’t expansionary will never reach us either.
Or one that doesn’t want to spend the energy ($$$) if other cheap energy forms we’ve speculated aren’t possible or as inexpensive/portable as would be needed.
They could just as easily be happy being billion year old zen masters, and we’d never know - even if they had warp drives.
They’d still exist though, and if we ever wanted to find them I guess we’d be able to do so. But we’d never know about them proactively.
Of course, there could be plenty of these floating around our solar system and we wouldn't know. They could be quite small and the solar system is quite big, and most of the proposed use cases for a civilization wanting to do this would not require it be in constant contact, so they might not even be broadcasting on anything resembling a frequent basis.
But in general there are a lot of theoretical technosignatures that we think we should be able to see if there was technological advanced life in the galaxy. (Should be able to see in that it is possible with our current technology - not that we would conclusively have seen it by this point.)
If you do the math, unless there are the aforementioned ‘cheat codes’, they frankly just don’t pencil out as worthwhile. No FTL/subspace? No ‘infinite cheap energy’ hack? No ‘infinite self replicating yet controllable builder of anything’ molecule?
No way to propagate, no way to energize, and no way to communicate at any real scale over the distances involved. Even gigawatt power, high efficiency, high precision aimed lasers aren’t going to have much luck at light year distances, and nothing is going to be useful for two way communication.
It’s easy to speculate of course, but like ‘grey goo’ it runs up against real issues with thermodynamics and physics if we stop and think about it much.
Worth investigating options of course, or talking about, but if physics is what it seems to be so far, that would perfectly explain the lack of us seeing them - they’re not useful/practical/worth the expense for anyone.
http://www.rfreitas.com/Astro/ComparisonReproNov1980.htm https://arxiv.org/ftp/arxiv/papers/2005/2005.12303.pdf
In general I do think it makes sense to not just contemplate interstellar visitors as living things making the trek or biological civilizations expanding, but there's a wide variety of artificial ~things~ that could end up in our solar system for whatever reason.
The only things we see self replicate are currently biological systems, and they can only do it under very specific circumstances and usually with a LOT of external help.
Circumstances which do not exist in space, let alone under the variety of environments on just the handful of planets we see in our solar system - except one, of course.
It's a very hard problem, and it isn't clear there is an actual answer that is economic to stick on the end of a rocket, even just to get to the moon. Something that survives 10k+ year journeys to unknown environments, and then does something useful? Even less clear.
Gets there AND then has the level of success necessary to transmit any sort of signal, or propagate itself further? Even less so.
Why we would do it, is also unclear.
Hopefully we'll figure out something that makes it less fantastical at some point - all the things that make it realistic would also help us in many other ways too!
We're in agreement that the 'why' is less clear, at least for probes exploring the galaxy. But there are some very clear reasons why this sort of tech in general is useful - mining the asteroid belt, building reflectors to better harness the energy of the sun, building all sorts of other infrastructure in space without having to use a rocket to get it there. At that point once we have the tech and are doing it - and I would be shocked if the human race is still around in 500 years and NOT doing that sort of thing - it's relatively cheap to kick off a bunch of probes doing similar things.
I'm still not sure if it's worth it in that scenario, but it's conceivable that it could be. And that puts us again on the question of why we don't see it. We think there should be a lot of intelligent life out there. There's a lot of very important 'if's in all of this, but if we can think of it and and conceive of some potential reasons, and if other intelligent life has these capabilities that we believe will be possible, and if it becomes as resource/energy/time efficient to do as it should be, then it seems like someone, somewhere, should have been able to convince their government or corporation or whatever to do it, even if the results aren't necessarily going to be super apparent. The Pioneer plaque is obviously much cheaper, but we knew beforehand that the utility there is basically 0%.
Like I said, I'm not necessarily arguing that these probes are out there. I'm guessing the answer is more likely "There's no compelling reason to colonize or even explore large swathes of the galaxy" and concerns around interstellar travel are on such large timescales that civilizations capable of interstellar travel would only care about their nearest neighbors. Maybe that changes as star formation spins down and the galaxy starts to slowly go dark and your local galactic resources are less and less abundant. I'm just saying that there are technosignatures that would indicate the presence of other intelligent life in the galaxy that have nothing to do with biological beings visiting us, and we would expect that some of these are possible for us to see now, if they're out there.
When we take numbers and probabilities in consideration it's good to also note how many hostile to life events can occur on a cosmic scale. You have supernovas, gamma ray bursts, black holes, neutron stars, magnetars, solar flares and coronal mass ejections, and a host of other shit we don’t even now about that could destroy life at any stage.
There are tens of millions of magnetars in the milky way and we can and do observe their "hiccups" - we've traded a multitude of GRBs back to stars we believe to be magnetars.
They do not have anywhere near enough energy to sterilize an entire galaxy.
If not for that one mutation under specific conditions and abundance of easily freeable oxygen, we’d still be goo in mud today. We were for 1.4 billion years until GOE happened.
It doesn’t mean that it cannot happen elsewhere. But there’s no clear linear route from complex acids to democracy. And maybe complex enough life requires a set of very special catastrophes. We can’t write off that we managed to evolve, but we can’t write off the exact procedure either.
It feels sad to look at a 2D image of the most 3D of all things.
"The Department of Physics at the University of Maryland, Baltimore County discovered that a large mass of gas is hurtling through the cluster at a speed of 750 km/s (466 miles/second). The mass is billions of solar masses, approximately 3 million light-years in diameter and is the largest of its kind discovered as of June 2006."
https://en.wikipedia.org/wiki/Faster-than-light
Patience ... is not sufficient in this case.
(It may still be all we have, and quite possibly more than we have.)
The equations that allow for wormholes or Alcubierre drives don't mean it's possible for living beings or working electronics to actually successfully make a trip through such extreme and unlikely phenomena.
It's a bit like saying you'll slingshot around a black hole close to its event horizon to gain enormous speed: you could do that, but tidal forces will rip you apart in the process. Except wormholes and other such spacetime anomalies are worse.
The bigger problem is finding such a black hole that doesn't have a very unfriendly to life and electronics accretion disk.
I've seen some arguments that alcubierre drives could allow for safe transportation with materials science advancements that we believe to be possible. Safe for the people traveling, at any rate. Not so safe for your destination and whatever else is in a large cone in front of your ship.
I've not seen any convincing arguments that would allow for anyone to safely traverse a worm hole, however.
As for Alcubierre drives, they’re interesting as a problem in highly speculative physics. But when people start taking as if we might actually build one, they lose me. I guess perhaps it’s kind of a fantasy game, like talking about gods, but if you’re not a believer or interested in playing the game, it just seems pointless. They’re not real and they’re extremely unlikely to ever be real.
Then we see the box that has the computer for controlling the fuel injection and ignition and start to take it apart to see how it works when one of us says:
"Stop. In broad terms, I can tell you how it works: It does what it needs to do so that the car can work. But by now we have gone so deep into how this car works that it is time to ask
What is the purpose of this car?"
The universe as it seems from current astronomy, ..., is one huge and intricate construction. Sorry, but tough to believe that all of this has no purpose.
Ah, two possibilities:
(1) We really are the center of the universe and the only life.
There is a lot less to the universe than what seems from current astronomy. In particular, objects we can never reach due to the speed of light limit are just fake, something like a painted screen.
(2) We have not found it yet, but there is a way to violate the speed of light. The whole universe is ours for the taking once we see how to exceed the speed of light. There is a game: For the laws of physics, how long will it take for life to develop to understand these laws and, in particular, how to exceed the speed of light?
For either of (1) or (2), maybe we should start a new subject, super cosmology, that assumes that the universe has a purpose. We look for that purpose and, for each discovery we make, e.g., dark matter, quantum mechanics, black holes, quasars, gravitational waves, ..., ask what its role is in the purpose of the universe.