My bet? Stars are strange. What we don't understand about stellar evolution really can't be overstated. Even where examples of it exist, we only get snapshots of the process which takes a great deal of time, and those snapshots are often utterly obscured by dust.
That's the number we can detect. Either intelligent life is extraordinarily rare, and we're the only local example, or it's fairly common and we just haven't detected it yet. I'd be much more surprised if we only discovered a single intelligent neighbor than if we discover a few hundred of them.
Or it's common, but it doesn't last once it starts developing the technology required to broadcast its presence, so we're all separated by time. We certainly don't appear likely to last very long, as a broadcasting species.
I want to know if our own star is also sending out these "peculiar periodic spectral modulations"??? If our own star is doing this as well, it could indicate that our solar system is a part of some type of "network", and these 234 stars would make excellent candidates in the search for intelligent life.
Our star does oscillate and we have studied its oscillations in great depth within asteroseismology (specifically helioseismology). But I'm overall doubtful of the conclusions of this paper, specifically the Fourier transforms they show don't appear special to me -- it looks like granulation background you get in effectively every star (though they do say they subtracted a "smoothed spectrum").
While I agree that it should be a late-stage hypothesis for simple Ockham's Razor reasons, there is absolutely nothing irrational nor supernatural about ET. Everything we know about life and about the universe, including the prevalence of Earth-sized and possibly Earth-like planets around other stars, makes ET an inductively obvious and very likely reality.
It's not confirmed yet, but it's a hypothesis that belongs in the same category as the Higgs Boson prior to the LHC: according to rest of what we know ETs should exist and we should expect to find evidence of this in some form someday.
It could come in the form of microbes or fossils on Mars, Titan, or Europa, or it could come in the form of a signal or even a probe or a spacecraft from the stars. The latter is IMHO no less likely. We exist and we send signals and space probes and pretty soon spacecraft. While we don't yet send these things very far, if we continue to develop as we have been we probably will someday. If we are a product of natural processes and those same processes are happening elsewhere (naturalistic metaphysics plus Kepler data says yes) then other things capable of sending signals or craft should exist elsewhere. Due to the age distribution of stars, some of them may have been around longer and therefore have had longer to evolve.
If anything the persistent absence of ET would suggest to me that modern science's fundamental understanding of reality may be incorrect. Either the theists are right, we're in a simulation (which is virtually identical to theism when you think about it), or something else profoundly strange is going on.
I attribute the intense skepticism of ETs to the silliness of much of UFO mythology. It's important to realize that the Rael cult and the abduction myth and so forth are a cultural phenomenon that has zero bearing on science one way or the other. Culture will take scientific ideas and hypotheses and run with them, and that's fine, but it shouldn't distract from reality or provoke an irrational backlash. Do we stop looking into "weird" possibilities in quantum physics because there are new agers who say silly things about QM? No, and we shouldn't dismiss aliens either. If we do we are actually letting pseudoscience and non-science dictate (in the negative) where science is willing to go.
If ETs are expected to be found, where are the Bracewell-von Neumann probes?
If any tech civilization ever launches a self-replicating interstellar probe, it would only take a few million years for the probes to reach every system in the galaxy. The observed lack of B-vN probes implies that no tech civilization has ever done so. And the probability of any civilization capable of launching B-vN probles actually doing so seems very high -- we'll be able to do it ourselves pretty soon.
You have to explain the lack of B-vN probes if you want to argue that ETs are/have been common.
(Scarier thought: if B-vN probes are inevitable, so are berserkers.)
I don't have time for this but I'd suggest looking into other discussions on this. The Fermi paradox opens an entire monstrous tree of possibilities, but it's not quite as simple as "there are no VN probes therefore there are no aliens."
My two favorites are:
(1) Interstellar travel might just be too damn hard. Going fast enough to get there in a reasonable time seems to require insane physicists' nightmare propulsion systems like antimatter or fusion rockets or artificial black hole drives, while taking too long means cosmic radiation has too much time to cook both organic matter and electronics... or you can't build a power source that will last that long, etc.
(2) The "uniform cooling hypothesis" -- maybe life is common but intelligences able to build (or become) VN probes are so far incredibly rare. Since the entire universe is (according to the leading theory) the same age, such things simply haven't happened yet.
(1) and (2) could work together-- maybe there are pretty advanced aliens everywhere but so far very few are advanced enough to attempt interstellar flight. If the probability of interstellar flight is less than, say, once per galaxy per billion years, then we would not see VN probes.
I don't buy (1). B-vN probes don't care about transit time or cost.
(2) is arguing for some kind of middle ground between "it's just us" and "lots of tech civs"; i.e., that life can get to the point of sending signals way easier than it can get to the point of launching a probe. But in our case the delta's just going to be a couple centuries, so no, that doesn't work for me either.
They're reasonable extrapolations from current capabilities. Build a self-replicating 3-D printer, make it capable of finding and refining raw materials on asteroids, slap it on a Voyager-like slow interstellar platform, and off you go.
(Yes, I'm being glib, but it's not that much of a stretch.)
If you use the earth as an analogy: why isn't every island on the earth populated with people, since humans are probes, self-replicating beings that communicate with others?
There's a lot of reasons there. Certain areas are unhabitable, or at least annoying to create a habitat (the arctic tundra, for example). Beings may want to cluster together (cities). There may be no interest in going to one territory over another - why bother spreading to all places, where there's so much out there?
Finally, you could have situations in which a probe or a highly advanced civilization could deliberately not contact a lesser-advanced civilizations. How do we know that we're not the less-advanced civilization? See: https://en.wikipedia.org/wiki/Uncontacted_peoples
I'm not sure how this is a counter to the human analogy? I'm assuming you're assuming probes reproduce and propagate perfectly, but if we assume a 'human reproductive unit' (be it a pregnant individual, a couple, a minimum viable population, whatever) has perfect genetics which can be perfectly replicated, then 'it just takes one' as well. While some sort of b-vn scenario seems plausible, at this point in technological development the practical contingencies of such a scheme are pretty up in the air. I mean, look at it from the other end. If we assume arbitrary technological progress, it's possible probes are everywhere, but we wouldn't even recognize them as technological artifacts if we were starring directly at them.
My favorite theory is an extension of #1: interstellar travel is so expensive and difficult that advances in AI and virtual reality make it undesirable. There's no point in spending a non-trivial fraction of your civilization's resources colonizing another solar system when you can do anything you want at arbitrary time scales in a simulation.
One other possible solution to the Fermi paradox is that the aliens exist, but they leave us alone, just like the Indian government leaves the Sentinel people alone.
> If ETs are expected to be found, where are the Bracewell-von Neumann probes?
Posing a question like "if [X] was expected, then how come we haven't found [very specific indicator of X]" does not make a lot of sense right now, neither from a logical point of view nor scientifically.
First of all, the absence of detectable vN probes does not somehow retroactively change the expectation we had for the presence of alien life, because that expectation arose from a statistical perspective on environmental and biological factors. Until invalidated, this is still the default expectation. It may well turn out that expectation was based on faulty assumptions at some point, but the deciding factor will not be the absence of your favorite arbitrary indicator.
It also makes no sense to stop looking based on the argument that we haven't found anything yet. Resolving the Fermi paradox is a higher stakes game than many people realize: Either we're just isolated from discovery for whatever reason (which would be fine as a class of explanations), or there is something fundamentally wrong about the universe.
Based on the information we have right now, ET must be out there. If it turns out he definitely isn't, we'd better find out why, because it's one of the biggest areas in modern science where prediction dramatically mismatches observed reality. We can't afford to just call off the search because we haven't found probes.
Not trying to be polemic here, but what then was the point of asking the question that way? I apologize if I read too much into it.
I think almost everybody agrees that looking for drones is a worthy endeavor, but it can't be the pivot point of the entire ET discussion for the simple reason that it's one more probability stacked on top of an already unknown probability (= the probability that any civilization will colonize the galaxy with a runaway drone program that can be easily detected). That's a very specific thing.
Depending on where you're coming from, you may assign a big probability to it, but there is by far no consensus. So for now the best we can do is to look at as many possible indicators as we can.
The grandparent of my comment was a suggestion that ETs should be an explanation of last resort for any unexplained phenomenon, which seems highly sensible to me and worthy of support.
If you enjoy probabilistic arguments, then you'll appreciate why I think that B-vN probes are inevitable.
If you believe that Nciv is large (and it's the number of tech civilizations up to now, not just at the moment), then you have to argue that P(civ launches one probe) is tiny if you agree that we haven't observed a probe here yet.
> If you enjoy probabilistic arguments, then you'll appreciate why I think that B-vN probes are inevitable.
You seem to be under the impression that I wasn't familiar with that argument, even though I explicitly described it as "the probability that any civilization will colonize the galaxy with a runaway drone program that can be easily detected". I don't think there is a person in this thread who doesn't understand the basic assumption.
Your claim of inevitability only applies to an infinite amount of time, so in our universe at this point in time the number can still be (and probably is) zero.
So I'm trying to talk about a more refined model instead, namely one that tries to at least reserve room for factors such as the overall number of active civilizations, and the likelihood that we actually discover a drone.
To start off with, we have no idea what the probability of a single civilization colonizing the galaxy with drones even is, and we're also making a lot of implicit assumptions about the nature of these drones. The argument that "one case is enough" is valid, but still the overall likelihood of that one very specific case may be too low.
There is also the possibility of drones going by undetected. We don't know what the drones' navigation algorithm would look like, but it's at least conceivable that some solar systems might have been left out altogether. Finally, I'm not sure if we could necessarily detect moderate drone activity in the outer solar system at all.
If ETs are expected to be found, where are the [extremely specific hypothetical construct that depends on certain technologies that may or may not be possible and a unique cultural context that isn't even universal to humanity, let alone all known life]?
I don't know. Maybe the vast, sentient ooze of distant moons doesn't understand why anyone would want to explore the universe. Maybe the dissipant entities of gas giants don't use materials commonly found in the rest of space for construction. Maybe the chittering hivemind of habitable worlds reached incredible advancement without developing a concept of individual intelligence, and thus has no understanding of how to make a single self-sufficient AI on a probe. Maybe there are more things in heaven and Earth than are dreamt of in etc.
IMO at least as plausible an answer is that species with the capabilities to produce such probes also have good reason not to do so.
We ourselves arguably have good reason not to broadcast our presence, reasons which we have come to belatedly but which are now widely known; e.g. the widely-cited belief that 'whenever' two cultures of significantly different technological prowess have interacted, the less-advanced one invariably went extinct / degraded / whatever.
I haven't read it yet but IIRC the Three-Body Problem trilogy proposes a universe in which advanced species stay silent for fear for just such interaction.
I can myself propose a variant idea, which is this: if we conclude from perceived silence/solitude that other species are likely out there but keeping their heads down,
...maybe we should do the same, not knowing what we might invite by broadcasting our presence.
If the first species to encounter this question incorrectly guessed its own probability of being first, and came to the same conclusion, we might actually be surrounded by a saturated sea of advanced species... all playing it unnecessarily safe...
I think you have a great point. Sorry you were downvoted.
I too see science being silly about aliens and ruling them out of bounds for a hypothesis space.
I see it like being on an island with no known wildlife. If you're trying to come up with hypotheses about why your food is dissapearing every night it would make sense to consider animals.
Not sure why you're getting downvoted here. You are correct: there is absolutely nothing irrational or supernatural about ET, and when looking for it we should consider ET as an explanation for any given phenomenon with as very low priority.
Most scientists agree that we should expect ET presence out there, it's just that opinions vary wildly about the probabilities involved.
Say a 1080p monitor display is completely randomized, until it shows a clear visible five-pointed star. Given I'm looking at a star, what is the likelihood there is another one on the screen? Practically 0, I'd think. Why is the emergence of an intelligent civilization in the universe different, assuming I take a multiverse and the anthropic principle seriously?
(In other words, given that a universe could have multiple intelligent civilizations, why is it the case that if I'm in a random sample with at least one, there is likely to be another?)
> Say a 1080p monitor display is completely randomized, until it shows a clear visible five-pointed star. Given I'm looking at a star, what is the likelihood there is another one on the screen?
That's an unnecessarily convoluted example, a way of asserting that you think the probability of a technological civilization arising is vanishingly small, and taking into account the vast time intervals in question, therefore unlikely for more than one to exist simultaneously.
Is that a valid point of view? Sure. It just means at least one of the factors in the Fermi equation is exceedingly small. Barring further evidence, that thesis may well turn out correct. But we still need to know what that inordinately small factor is, because we haven't found anything that fits the bill yet. Granted, there are big questions about the probability of things like abiogenesis, but over the entire history of science, arguments from exceptionality or uniqueness have almost always turned out to be incorrect.
> a way of asserting that you think the probability of a technological civilization arising is vanishingly small
I have no idea one way or another. I wonder why many scientists are confident that extraterrestrial intelligent life exists though. Viewing through the lens of one example in a random (otherwise) unremarkable multiverse, it's not clear to me why this should be so.
You are right, it's a perfectly valid hypothesis, but it is an almost useless one, for at least two reasons.
* It is improbable.
Say I hear what appears to be a human being, but whom I cannot identify. It may be Roger Waters, there's nothing supernatural here, there's no reason why it couldn't be him. Yet, there are so many other people around that this hypothesis is totally useless: it very likely isn't Roger Waters, so I'm better off without it.
* It is very hard to prove / disprove
Intelligent, technologically advanced beings could very probably generate a wide variety of signals, so it is hard to prove that a certain signal cannot be generate by them; we also have no idea how the "typical" ET signal looks like, so the hypothesis doesn't really help us in furthering our analysis.
Regarding your first point, the trouble (at least in this instance) is that this logic doesn't apply when you're looking for Roger Waters and calling everyone in the phone book with his name. Each time someone picks up the phone it probably won't be the person you're looking for, but you certainly had reason to believe they could be.
They didn't find a strange phenomenon and point out it might be ETI, in which case you're right, the hypothesis wouldn't make sense until you had ruled out basically everything else. They made a hypothesis about what ETI would look like, looked for it, and claim to have found things that could fit the bill.
Sure, and if we hear a very distinct voice singing and/or guitar or bass playing, we may identify Roger Waters. If we hear footsteps? Probably not Roger Waters.
I'm skeptical of ET that:
1.) Is stupid enough to broadcast to a big, unknown universe
2.) Is alive and technologically capable at the same time we are
3.) That we're going to be around and looking to the skies for very long, relatively speaking.
Personally I find some version of the Great Filter hypothesis very compelling.
We still have no idea what carries the force observed as inertia. While it may be a hypothesis that aliens exist, it's also a hypothesis that they don't. We know things have inertia, but have no idea why they do. We have a reasonable assumption that aliens exist. Proving they exist consists of finding an alien civilization, but proving they don't would include an exhaustive search of the entire universe. Inertia appears to be a universal force, but proving that would also require an fairly exhaustive search from everywhere in the universe.
Sure, but if we're going to look let's look in those places that are generating the kind of evidence we'd expect to see which are showing interesting behavior.
There's room for debate but it generally seems to match our observations. There's no a priori reason to believe that Earth is special in the universe since all the rest of our solar system / galaxy seem to be unremarkable.
No, they find it more probable that these particular signals are not aliens. It's not about whether or not you believe aliens exist, at all, it's about whether or not their the best explanation for any phenomenon. One day, we may get evidence for which there is no better explanation (say, a flying saucer landing at the White House with little grey aliens hopping out.) Right now, we do not have to use that hypothesis of last resort; it's still more parsimonious to think we just don't understand stars that well.
It's shame this is downvoted because it's the key insight of the two propositions:
1. the lack of ET-evidence is really odd and could be indicative of a barren universe
2. The outcome of 1 civ / universe is a really odd output (vs. a zero/many civs) from a Drake-equation-like natural, random universe.
Which should, if we can fill in the gaps to the above sketchy proof, cause the most rational among us to wrestle with the idea if we really know what's going on.
I'd add the other most salient fact is how quickly we're gaining the ability to examine proposition #1, by say in this case, datamining astronomy data sets...
3. In a few decades we'll have a pretty exhaustive survey of exoplanets that should find a TruePositive if there are some to find, heck even a photosynthesizing planet in the galaxy should suffice.
Taken together, there should be some philophizing about the idea that we could end up proving ourselves to be alone, all within the forseeable future, while we're still all still on Earth.
Thank you for realizing my gist. I believe the possibility of 1 civ/universe to be so odd that I cannot believe it's true. Problem is, once you accept that, now you're in uncharted territory. Are these hypothetical ET's far away? Are they pre-sentient? Or are they already here somehow (alcubierre drive?) and all those people claiming UFO sightings and/or encounters are in fact, in large part, correct? :O
Why aren't they including random chance into the possible explanations?
I might not understand this correctly, but out of 2.5 million stars, the ~240 they found to match their expected pattern could just be the random hit rate of this pattern among stars, .0096%.
The most charitable interpretation I can then offer is that it is masturbation. Nothing wrong with masturbation, of course, but it's rather unseemly to do it in public.
The correct answer would have been to pick a reasonable assumption (before you ask, your own judgement determines what is reasonable) for what "useful" is, and to clarify that that was the assumption you were using.
We don't have to question whether or not anything means anything in order to engage with every topic every time, but I appreciate the exercise.
You are pretty much spot-on with matching up to my statement. Implicit in your claim is that science has an expectation, which is a gross conceptual error. The down-votes suggest you are not the only one.
This (https://arxiv.org/abs/1210.5986) is his 2012 paper where the method used here is justified. Also gives a short summary of SETI efforts in the introduction. He discussed the energy requirements to send a signal of the type described so it can be detected at 1000ly, which seem reasonable.
I am quoting from there: "The international SETI community has established a 0 to 10 scale for quantifying detections of phenomena that may indicate the existence of advanced life beyond the Earth called the "Rio Scale". The BSRC team
assesses the Borra-Trottier result to currently be a 0 or 1 (None/Insignificant) on this scale. If the signal were
to be confirmed with another independent telescope, its significance would rise, though an exhaustive
analysis of other possible explanations, including instrumental phenomena, must be performed before
supporting the hypothesis that artificially generated pulses are responsible for the claimed signal."
phys.org - as usual - barely mentions what the signal even is, and contains no information about the structure of those pulses (instead they chose to show one of the least relevant bar graphs I've ever seen twice, probably because it looks "signally").
Signals having the same period were found in only 234 stars overwhelmingly in the F2 to K1 spectral range.
Why would they expect signals from 100's of different stars to have the same period ? Doesn't this suggest some sort of instrumental or analysis artifact ?
Why would we expect a subset of supernovae to have exactly the same peak luminosity no matter where they are and what stars they occur in? Instrument artifact, or previously-unknown outcome of the physical laws of the universe?
What I'm really questioning is their ETI hypothesis. How do they explain that 100's of different civilizations would all choose the same modulation period ?
The difference is that asteroseismology (which comes from hydrodynamics) predicts that the oscillation frequencies of stars are determined by several factors intrinsic to the star. We therefore don't expect many different kinds of stars to have similar oscillation frequencies (though the oscillations themselves may have similarities such as the scaling relation for solar-like oscillators).
I don't know much about the actual physics behind supernovae but I'm fairly sure that the maths makes the power predictions that we observe.
Are all the star systems blinking in much the same way? If so, that suggests a natural phenomenon. Or there is a vast interstellar empire with a fascination for sending out the same kind of pulsed signals. Which pretty much tips it towards natural phenomenon.
Does anyone understand the chart enough in the original paper to correlate the plate ID's with specific named stars? I'm curing to know the distance some of these stars are to us.
Ignoring the quite unconventional formatting (single column, figures at the end with the references), I'm not entirely convinced by the plots at the end of the paper. Specifically, their examples of "odd" Fourier transforms look quite normal. Specifically, the noise level (how it looks like a power function) is related to the "granulation background" of the star and is predicted by asteroseismic stellar models (the equations are ugly but they do exist). Normally you remove them from your transforms before you do anything with them. To be fair, they did say they "subtracted a smooth spectrum" but the noise level doesn't look flat enough to me. Also, their Fourier transforms are in super funky units -- in asteroseismology you generally want to use PSFs (Power Spectral Frequency, where the y axis is P/Hz).
99 comments
[ 3.8 ms ] story [ 178 ms ] threadhttps://en.wikipedia.org/wiki/Betteridge%27s_law_of_headline...
"Are 234 aliens trying to contact us??"
It is the modern equivalent of blaming the gods for a natural disaster.
While I agree that it should be a late-stage hypothesis for simple Ockham's Razor reasons, there is absolutely nothing irrational nor supernatural about ET. Everything we know about life and about the universe, including the prevalence of Earth-sized and possibly Earth-like planets around other stars, makes ET an inductively obvious and very likely reality.
It's not confirmed yet, but it's a hypothesis that belongs in the same category as the Higgs Boson prior to the LHC: according to rest of what we know ETs should exist and we should expect to find evidence of this in some form someday.
It could come in the form of microbes or fossils on Mars, Titan, or Europa, or it could come in the form of a signal or even a probe or a spacecraft from the stars. The latter is IMHO no less likely. We exist and we send signals and space probes and pretty soon spacecraft. While we don't yet send these things very far, if we continue to develop as we have been we probably will someday. If we are a product of natural processes and those same processes are happening elsewhere (naturalistic metaphysics plus Kepler data says yes) then other things capable of sending signals or craft should exist elsewhere. Due to the age distribution of stars, some of them may have been around longer and therefore have had longer to evolve.
If anything the persistent absence of ET would suggest to me that modern science's fundamental understanding of reality may be incorrect. Either the theists are right, we're in a simulation (which is virtually identical to theism when you think about it), or something else profoundly strange is going on.
I attribute the intense skepticism of ETs to the silliness of much of UFO mythology. It's important to realize that the Rael cult and the abduction myth and so forth are a cultural phenomenon that has zero bearing on science one way or the other. Culture will take scientific ideas and hypotheses and run with them, and that's fine, but it shouldn't distract from reality or provoke an irrational backlash. Do we stop looking into "weird" possibilities in quantum physics because there are new agers who say silly things about QM? No, and we shouldn't dismiss aliens either. If we do we are actually letting pseudoscience and non-science dictate (in the negative) where science is willing to go.
If any tech civilization ever launches a self-replicating interstellar probe, it would only take a few million years for the probes to reach every system in the galaxy. The observed lack of B-vN probes implies that no tech civilization has ever done so. And the probability of any civilization capable of launching B-vN probles actually doing so seems very high -- we'll be able to do it ourselves pretty soon.
You have to explain the lack of B-vN probes if you want to argue that ETs are/have been common.
(Scarier thought: if B-vN probes are inevitable, so are berserkers.)
I don't have time for this but I'd suggest looking into other discussions on this. The Fermi paradox opens an entire monstrous tree of possibilities, but it's not quite as simple as "there are no VN probes therefore there are no aliens."
My two favorites are:
(1) Interstellar travel might just be too damn hard. Going fast enough to get there in a reasonable time seems to require insane physicists' nightmare propulsion systems like antimatter or fusion rockets or artificial black hole drives, while taking too long means cosmic radiation has too much time to cook both organic matter and electronics... or you can't build a power source that will last that long, etc.
(2) The "uniform cooling hypothesis" -- maybe life is common but intelligences able to build (or become) VN probes are so far incredibly rare. Since the entire universe is (according to the leading theory) the same age, such things simply haven't happened yet.
(1) and (2) could work together-- maybe there are pretty advanced aliens everywhere but so far very few are advanced enough to attempt interstellar flight. If the probability of interstellar flight is less than, say, once per galaxy per billion years, then we would not see VN probes.
Neither (1) nor (2) rules out signals at all.
(2) is arguing for some kind of middle ground between "it's just us" and "lots of tech civs"; i.e., that life can get to the point of sending signals way easier than it can get to the point of launching a probe. But in our case the delta's just going to be a couple centuries, so no, that doesn't work for me either.
(Yes, I'm being glib, but it's not that much of a stretch.)
There's a lot of reasons there. Certain areas are unhabitable, or at least annoying to create a habitat (the arctic tundra, for example). Beings may want to cluster together (cities). There may be no interest in going to one territory over another - why bother spreading to all places, where there's so much out there?
Finally, you could have situations in which a probe or a highly advanced civilization could deliberately not contact a lesser-advanced civilizations. How do we know that we're not the less-advanced civilization? See: https://en.wikipedia.org/wiki/Uncontacted_peoples
How sure are you that you are not (part of) one?
I think the parent was suggesting directed panspermia-- that the Earth's biosphere is itself a B-vN probe in the process of self-replication.
That's one way to do it.
If there are ETs, I really want to know whether they're using DNA with triplet codons that map to the same 20 amino acids.
Sure cells can reproduce but they can't build spaceships.
Posing a question like "if [X] was expected, then how come we haven't found [very specific indicator of X]" does not make a lot of sense right now, neither from a logical point of view nor scientifically.
First of all, the absence of detectable vN probes does not somehow retroactively change the expectation we had for the presence of alien life, because that expectation arose from a statistical perspective on environmental and biological factors. Until invalidated, this is still the default expectation. It may well turn out that expectation was based on faulty assumptions at some point, but the deciding factor will not be the absence of your favorite arbitrary indicator.
It also makes no sense to stop looking based on the argument that we haven't found anything yet. Resolving the Fermi paradox is a higher stakes game than many people realize: Either we're just isolated from discovery for whatever reason (which would be fine as a class of explanations), or there is something fundamentally wrong about the universe.
Based on the information we have right now, ET must be out there. If it turns out he definitely isn't, we'd better find out why, because it's one of the biggest areas in modern science where prediction dramatically mismatches observed reality. We can't afford to just call off the search because we haven't found probes.
I think almost everybody agrees that looking for drones is a worthy endeavor, but it can't be the pivot point of the entire ET discussion for the simple reason that it's one more probability stacked on top of an already unknown probability (= the probability that any civilization will colonize the galaxy with a runaway drone program that can be easily detected). That's a very specific thing.
Depending on where you're coming from, you may assign a big probability to it, but there is by far no consensus. So for now the best we can do is to look at as many possible indicators as we can.
If you enjoy probabilistic arguments, then you'll appreciate why I think that B-vN probes are inevitable.
If you believe that Nciv is large (and it's the number of tech civilizations up to now, not just at the moment), then you have to argue that P(civ launches one probe) is tiny if you agree that we haven't observed a probe here yet.You seem to be under the impression that I wasn't familiar with that argument, even though I explicitly described it as "the probability that any civilization will colonize the galaxy with a runaway drone program that can be easily detected". I don't think there is a person in this thread who doesn't understand the basic assumption.
Your claim of inevitability only applies to an infinite amount of time, so in our universe at this point in time the number can still be (and probably is) zero.
So I'm trying to talk about a more refined model instead, namely one that tries to at least reserve room for factors such as the overall number of active civilizations, and the likelihood that we actually discover a drone.
To start off with, we have no idea what the probability of a single civilization colonizing the galaxy with drones even is, and we're also making a lot of implicit assumptions about the nature of these drones. The argument that "one case is enough" is valid, but still the overall likelihood of that one very specific case may be too low.
There is also the possibility of drones going by undetected. We don't know what the drones' navigation algorithm would look like, but it's at least conceivable that some solar systems might have been left out altogether. Finally, I'm not sure if we could necessarily detect moderate drone activity in the outer solar system at all.
Seriously? We probably shot them down: https://www.youtube.com/watch?v=cZWs8116Q-E
Funny that...
Anyway there's a bunch of these "pilot encounters UFO with description not matching any known aircraft" stories.
http://ufos.about.com/od/bestufocasefiles/p/mantell.htm
I don't know. Maybe the vast, sentient ooze of distant moons doesn't understand why anyone would want to explore the universe. Maybe the dissipant entities of gas giants don't use materials commonly found in the rest of space for construction. Maybe the chittering hivemind of habitable worlds reached incredible advancement without developing a concept of individual intelligence, and thus has no understanding of how to make a single self-sufficient AI on a probe. Maybe there are more things in heaven and Earth than are dreamt of in etc.
We ourselves arguably have good reason not to broadcast our presence, reasons which we have come to belatedly but which are now widely known; e.g. the widely-cited belief that 'whenever' two cultures of significantly different technological prowess have interacted, the less-advanced one invariably went extinct / degraded / whatever.
I haven't read it yet but IIRC the Three-Body Problem trilogy proposes a universe in which advanced species stay silent for fear for just such interaction.
I can myself propose a variant idea, which is this: if we conclude from perceived silence/solitude that other species are likely out there but keeping their heads down,
...maybe we should do the same, not knowing what we might invite by broadcasting our presence.
If the first species to encounter this question incorrectly guessed its own probability of being first, and came to the same conclusion, we might actually be surrounded by a saturated sea of advanced species... all playing it unnecessarily safe...
<shrug>
I too see science being silly about aliens and ruling them out of bounds for a hypothesis space.
I see it like being on an island with no known wildlife. If you're trying to come up with hypotheses about why your food is dissapearing every night it would make sense to consider animals.
Most scientists agree that we should expect ET presence out there, it's just that opinions vary wildly about the probabilities involved.
(In other words, given that a universe could have multiple intelligent civilizations, why is it the case that if I'm in a random sample with at least one, there is likely to be another?)
That's an unnecessarily convoluted example, a way of asserting that you think the probability of a technological civilization arising is vanishingly small, and taking into account the vast time intervals in question, therefore unlikely for more than one to exist simultaneously.
Is that a valid point of view? Sure. It just means at least one of the factors in the Fermi equation is exceedingly small. Barring further evidence, that thesis may well turn out correct. But we still need to know what that inordinately small factor is, because we haven't found anything that fits the bill yet. Granted, there are big questions about the probability of things like abiogenesis, but over the entire history of science, arguments from exceptionality or uniqueness have almost always turned out to be incorrect.
I have no idea one way or another. I wonder why many scientists are confident that extraterrestrial intelligent life exists though. Viewing through the lens of one example in a random (otherwise) unremarkable multiverse, it's not clear to me why this should be so.
* It is improbable.
Say I hear what appears to be a human being, but whom I cannot identify. It may be Roger Waters, there's nothing supernatural here, there's no reason why it couldn't be him. Yet, there are so many other people around that this hypothesis is totally useless: it very likely isn't Roger Waters, so I'm better off without it.
* It is very hard to prove / disprove
Intelligent, technologically advanced beings could very probably generate a wide variety of signals, so it is hard to prove that a certain signal cannot be generate by them; we also have no idea how the "typical" ET signal looks like, so the hypothesis doesn't really help us in furthering our analysis.
They didn't find a strange phenomenon and point out it might be ETI, in which case you're right, the hypothesis wouldn't make sense until you had ruled out basically everything else. They made a hypothesis about what ETI would look like, looked for it, and claim to have found things that could fit the bill.
Personally I find some version of the Great Filter hypothesis very compelling.
That would be the best proof of a(n absentee) God ever, basically. The one special planet deemed OK to magic-pixie-dust life onto!
Which makes me presume it to be false.
So far there is no evidence of life beyond this planet. Until there is that hypothesis should be viewed with skepticism.
https://en.wikipedia.org/wiki/Cosmological_principle
There's room for debate but it generally seems to match our observations. There's no a priori reason to believe that Earth is special in the universe since all the rest of our solar system / galaxy seem to be unremarkable.
1. the lack of ET-evidence is really odd and could be indicative of a barren universe
2. The outcome of 1 civ / universe is a really odd output (vs. a zero/many civs) from a Drake-equation-like natural, random universe.
Which should, if we can fill in the gaps to the above sketchy proof, cause the most rational among us to wrestle with the idea if we really know what's going on.
I'd add the other most salient fact is how quickly we're gaining the ability to examine proposition #1, by say in this case, datamining astronomy data sets...
3. In a few decades we'll have a pretty exhaustive survey of exoplanets that should find a TruePositive if there are some to find, heck even a photosynthesizing planet in the galaxy should suffice.
Taken together, there should be some philophizing about the idea that we could end up proving ourselves to be alone, all within the forseeable future, while we're still all still on Earth.
I might not understand this correctly, but out of 2.5 million stars, the ~240 they found to match their expected pattern could just be the random hit rate of this pattern among stars, .0096%.
We don't have to question whether or not anything means anything in order to engage with every topic every time, but I appreciate the exercise.
> Stars are. Only human perception can be "red, and giant".
We describe things using metaphors and concepts that make sense in our world. So what's your point?
I am quoting from there: "The international SETI community has established a 0 to 10 scale for quantifying detections of phenomena that may indicate the existence of advanced life beyond the Earth called the "Rio Scale". The BSRC team assesses the Borra-Trottier result to currently be a 0 or 1 (None/Insignificant) on this scale. If the signal were to be confirmed with another independent telescope, its significance would rise, though an exhaustive analysis of other possible explanations, including instrumental phenomena, must be performed before supporting the hypothesis that artificially generated pulses are responsible for the claimed signal."
phys.org - as usual - barely mentions what the signal even is, and contains no information about the structure of those pulses (instead they chose to show one of the least relevant bar graphs I've ever seen twice, probably because it looks "signally").
So this is the actual paper: http://iopscience.iop.org/article/10.1088/1538-3873/128/969/...
I'm going to have to read that now, but if these pulses are as stupidly regular as hinted, there is probably nothing to see here.
Signals having the same period were found in only 234 stars overwhelmingly in the F2 to K1 spectral range.
Why would they expect signals from 100's of different stars to have the same period ? Doesn't this suggest some sort of instrumental or analysis artifact ?
What I'm really questioning is their ETI hypothesis. How do they explain that 100's of different civilizations would all choose the same modulation period ?
I don't know much about the actual physics behind supernovae but I'm fairly sure that the maths makes the power predictions that we observe.
This is how science actually works.
Ignoring the quite unconventional formatting (single column, figures at the end with the references), I'm not entirely convinced by the plots at the end of the paper. Specifically, their examples of "odd" Fourier transforms look quite normal. Specifically, the noise level (how it looks like a power function) is related to the "granulation background" of the star and is predicted by asteroseismic stellar models (the equations are ugly but they do exist). Normally you remove them from your transforms before you do anything with them. To be fair, they did say they "subtracted a smooth spectrum" but the noise level doesn't look flat enough to me. Also, their Fourier transforms are in super funky units -- in asteroseismology you generally want to use PSFs (Power Spectral Frequency, where the y axis is P/Hz).