Some thoughts on the Fermi paradox

[keenir]

I can have a penpal that I write to all the time, back and forth, across entire continents......whether I'm writing the letters now with UPS or in the Victorian age with steam boats, relativity and plate tectonics (etc) don't matter if you're going back and forth between two points.

What if you're trying to keep in touch with Dr Livingstone while he's on his travels?

I imagine the method IRL used was "go to the ports and cities where he was, then follow the trail he left"

after all, didn't Victorian England follow his travels - even if not as-they-happened - then at least keeping up with the first half before he returned to England?

This SOS-using civilisation sounds as though it's flitting from star to star.

...which kinda disqualifies it from the "galactic" title.

seriously, if we know that, barring unforeseen mishaps, the civilization's ships will be heading along a certain pathway or arc or whatever...then we can aim in that direction.....not sirens blaring in all directions, but somewhat broadly.

[rotting bones]

Well, I had been thinking in terms of FM rather than AM. However, the key point lies in error-correcting codes. As the length of the message is not very long, by repeating the message and using a suitable error correcting code, one can drastically reduce the signal level needed to get the message through. The key to detecting such a message is to know what code to apply. If one thinks of the signal as string of 1's and 0's, reading them correctly a random 50.1% of the time is good enough to get the message through.

So there's a repeating noisy signal hidden in the frequency domain that is detected by error correction codes. But such a signal would have to be identified by its amplitude. The amplitude can't be constant, so it must vary in a culturally predetermined order. The question is whether that order is complex enough to evade detection. Do undetectable signals of the kind you're talking about have real world applications? If so, then we can consult what experts think of their limitations.

?

From the post you quoted:

What's weird about distributed resource allocation? It is standard technology: https://arxiv.org/abs/1409.2475 https://scholar.google.com/scholar?hl=e ... tion&btnG=

In these systems, nodes in the network send messages to their neighbors without having direct knowledge of their internal states. Nodes can even fail right in the heart of the network, but the algorithm is designed so that everything works out anyway in the long run.

no, I'm pointing out that I - like others - do not have the same presumptions you seem to have.

Again, I have no idea what you're talking about. If you read this thread, you'll find that the civilization I'm talking about would typically send much more than bare SOS signals. This whole line of thinking is hypothetical:

That depends on the structure of the message. It needs to be recognized as artificial by the recipient. Whatever header marks it as such is likely to be highly ordered, since that is its one job. As for the contents, a record of goods produced and list of requirements would resemble a sequence of numbers when decompressed. Of course, the contents will almost certainly be somewhat compressed, and that will increase its entropy.

PS. Even if it's just an SOS message, it has to be such that the intended recipient can't mistake it for a natural radio emission. If they can't mistake it, then why can we?

How can I be imposing my presuppositions in a hypothetical line of thinking?

[keenir]

Again, I have no idea what you're talking about. If you read this thread, you'll find that the civilization I'm talking about would typically send much more than bare SOS signals. This whole line of thinking is hypothetical:

That depends on the structure of the message. It needs to be recognized as artificial by the recipient. Whatever header marks it as such is likely to be highly ordered, since that is its one job. As for the contents, a record of goods produced and list of requirements would resemble a sequence of numbers when decompressed. Of course, the contents will almost certainly be somewhat compressed, and that will increase its entropy.

PS. Even if it's just an SOS message, it has to be such that the intended recipient can't mistake it for a natural radio emission. If they can't mistake it, then why can we?

because we didn't know to look for it -- thats the whole point of sending a message...they're sending sports scores, you're hearing a mondegreen and think its an SOS.

How can I be imposing my presuppositions in a hypothetical line of thinking?

you mean besides using your presuppositions as the assumed default for what is rational for a civilization?

you're also taking offense when I pointed out to you that not everyone thinks like you -- you outright asked me if I was insulting you.

The idea that they will ever make it out of the wilds sounds like an overly optimistic assessment to me. That is a grossly inefficient form of communication in terms of range, time and resource expenditure.

...to which I pointed out that social cues and such, seem equally grossly inefficient forms of communication -- and you got mad.

If a predator is approaching, you have to get back to your tribe and hand the first individual a scented wax.

I know some forms of government advocate giving everything to everyone equally, but your example makes utterly no sense.

The entire tribe will then have to finish handing each other scented waxes, depleting who knows how much nutrition. Over galactic distances, material signs will of course be slower than light speed without FTL.

except your galactic civilization falls apart no matter whether they use material signs or radio or whatever. because you're sending the radio "waxes" to everyone in every direction, regardless of if they are there or if they can help.

[rotting bones]

because we didn't know to look for it -- thats the whole point of sending a message...they're sending sports scores, you're hearing a mondegreen and think its an SOS.

The point is not to decide whether the message is an SOS. The point is to find a signal, any signal, that credibly originated among intelligent life.

you mean besides using your presuppositions as the assumed default for what is rational for a civilization?

you're also taking offense when I pointed out to you that not everyone thinks like you -- you outright asked me if I was insulting you.

I'm sorry if that's how I came across. I didn't think you were being serious.

...to which I pointed out that social cues and such, seem equally grossly inefficient forms of communication -- and you got mad.

Whether inefficient forms of communication exist is not relevant to the question of whether efficient forms can be deployed when needed.

I know some forms of government advocate giving everything to everyone equally, but your example makes utterly no sense.

except your galactic civilization falls apart no matter whether they use material signs or radio or whatever. because you're sending the radio "waxes" to everyone in every direction, regardless of if they are there or if they can help.

I disagree. I don't feel like elaborating.

[keenir]

because we didn't know to look for it -- thats the whole point of sending a message...they're sending sports scores, you're hearing a mondegreen and think its an SOS.

The point is not to decide whether the message is an SOS. The point is to find a signal, any signal, that credibly originated among intelligent life.

but how can you distinguish a natural signal from a mondegreen that just sounds like a natural signal?

you mean besides using your presuppositions as the assumed default for what is rational for a civilization?

you're also taking offense when I pointed out to you that not everyone thinks like you -- you outright asked me if I was insulting you.

I'm sorry if that's how I came across. I didn't think you were being serious.

by and large, I'm frequently serious...its how my brain is wired.

...to which I pointed out that social cues and such, seem equally grossly inefficient forms of communication -- and you got mad.

Whether inefficient forms of communication exist is not relevant to the question of whether efficient forms can be deployed when needed.

except your assumption is you know what is and isn't efficient forms of communication -- such as wanting to broadcast a signal in every direction, despite that being a hideously expensive and mind-numbingly wasteful use of energy that will taper off faster than anything.

I know some forms of government advocate giving everything to everyone equally, but your example makes utterly no sense.

except your galactic civilization falls apart no matter whether they use material signs or radio or whatever. because you're sending the radio "waxes" to everyone in every direction, regardless of if they are there or if they can help.

I disagree. I don't feel like elaborating.

so...you surrender?

I don't even know which part of my statement you're disagreeing with, so I don't know which part you're open to discussing further & which parts you aren't.

[Ares Land]

The problem is that there is no sign of ordered signals anywhere across the universe. We've seen plenty of anomalies that point to holes in our cosmological models, but none of them credibly point to intelligent life.

There's no way we can say that: the universe is actually a pretty big place.

I'd rephrase that as: in our galactic neighborhood, we found no trace of very strong signals or of weaker signals in a select band of frequencies that would be good for interstellar communication.

Let's keep in mind that:
- Our detection range is actually small. I think you mentioned 150 ly? That's tiny compared to the galaxy, which is itself a negligible bit of matter compared to the universe.
- There are reasons why an alien civilization's signals wouldn't be detectable which make a good deal of sense, like for instance, preferring cables at home and very tight communication beams in space.
- It's possible an alien species could broadcast signals, but that requires a specific set of conditions and it's entirely possible these don't obtain in our galactic neighborhood.
- Interstellar communication is best handles through methods that we aren't aware of, or don't look for.
- The density of advanced civilizations is fairly low, and there isn't one within 150 ly. Which seems pretty likely! (and it still means there could be quite a few in the galaxy).

So, yeah, basically the fact that we haven't found anything doesn't especially cry out for special explanation.

[Pabappa]

The size of the universe is unknown .... the observable universe is something like 90 billion light years across, which is already huge, but that isn't the edge of the universe any more than the horizon is the edge of the planet.

We only have one real data point to go on if we want to even so much as guess at the full size of the universe .... if primordial quantum fluctuations are the cause of the large-scale temperature variations we see in the cosmic microwave background today, we can scale up present-day quantum phenomena to estimate the present size of the universe. Even this leaves wide room for debate, though, as scientists have used it to say that the full size may be anywhere from only a few hundred times larger than the observable universe (not much of a difference when dealing with such large numbers everywhere else) to 3 × 10²³ times larger. And I think that latter number is just the diameter, so it would need to be cubed as well.

Even if our own observable universe turns out to be surprisingly barren, there's all that other space to consider. Yes, this would require a good mechanism of faster-than-light travel to be meaningful, but so would travel from within most of the observable universe. If we assume the FTL barrier is breakable, it really doesnt matter if the number of light-years needing to be traveled is in the millions, billions, or trillions.

[WeepingElf]

The problem is that there is no sign of ordered signals anywhere across the universe. We've seen plenty of anomalies that point to holes in our cosmological models, but none of them credibly point to intelligent life.

There's no way we can say that: the universe is actually a pretty big place.

I'd rephrase that as: in our galactic neighborhood, we found no trace of very strong signals or of weaker signals in a select band of frequencies that would be good for interstellar communication.

Let's keep in mind that:
- Our detection range is actually small. I think you mentioned 150 ly? That's tiny compared to the galaxy, which is itself a negligible bit of matter compared to the universe.
- There are reasons why an alien civilization's signals wouldn't be detectable which make a good deal of sense, like for instance, preferring cables at home and very tight communication beams in space.
- It's possible an alien species could broadcast signals, but that requires a specific set of conditions and it's entirely possible these don't obtain in our galactic neighborhood.
- Interstellar communication is best handles through methods that we aren't aware of, or don't look for.
- The density of advanced civilizations is fairly low, and there isn't one within 150 ly. Which seems pretty likely! (and it still means there could be quite a few in the galaxy).

So, yeah, basically the fact that we haven't found anything doesn't especially cry out for special explanation.

AMEN. There are so many reasons why we can't find them that not all of them need to hold to explain why we haven't found anything yet.

[zompist]

Even this leaves wide room for debate, though, as scientists have used it to say that the full size may be anywhere from only a few hundred times larger than the observable universe (not much of a difference when dealing with such large numbers everywhere else) to 3 × 10²³ times larger.

Earlier in this thread I looked this up, and I was surprised at the theoretical variation. We don't even know if the universe is finite or not.

If we assume the FTL barrier is breakable, it really doesnt matter if the number of light-years needing to be traveled is in the millions, billions, or trillions.

That depends on the cost and speed of travel.

For narrative reasons, most sf imagines huge multiples of lightspeed. It might be interesting to have a con-universe where the max speed is 4c, and the costs are similar to (say) oil tankers.

[Richard W]

Well, I had been thinking in terms of FM rather than AM. However, the key point lies in error-correcting codes. As the length of the message is not very long, by repeating the message and using a suitable error correcting code, one can drastically reduce the signal level needed to get the message through. The key to detecting such a message is to know what code to apply. If one thinks of the signal as string of 1's and 0's, reading them correctly a random 50.1% of the time is good enough to get the message through.

So there's a repeating noisy signal hidden in the frequency domain that is detected by error correction codes. But such a signal would have to be identified by its amplitude. The amplitude can't be constant, so it must vary in a culturally predetermined order. The question is whether that order is complex enough to evade detection. Do undetectable signals of the kind you're talking about have real world applications? If so, then we can consult what experts think of their limitations.

You wouldn't identify such a signal by its amplitude. Typically these signals are implemented by some kind of phase or frequency modulation. The two types of real world system I have in mind are LPI radars and the likes of the New Horizons downlink. The latter uses very low data rates, and occupies a bandwidth about six times the data rate to carry the 'turbo-coded' signal.

[rotting bones]

I'd rephrase that as: in our galactic neighborhood, we found no trace of very strong signals or of weaker signals in a select band of frequencies that would be good for interstellar communication.

Yes, I wrote that somewhat loosely. We haven't found natural signals definitively pointing to artificial development either. True, artificial signals are less likely if galactic civilizations are impossible. But if galactic civilizations are impossible, then contact is also less interesting.

- Our detection range is actually small. I think you mentioned 150 ly? That's tiny compared to the galaxy, which is itself a negligible bit of matter compared to the universe.

10^4 lys were cleared by the 70's.

You wouldn't identify such a signal by its amplitude. Typically these signals are implemented by some kind of phase or frequency modulation. The two types of real world system I have in mind are LPI radars and the likes of the New Horizons downlink. The latter uses very low data rates, and occupies a bandwidth about six times the data rate to carry the 'turbo-coded' signal.

No, I don't get it. Given that this is a use case where we're trying to avoid false positives, if you're unwilling to restrict the amplitude, you must do it to the frequency range in order to cut down on noise. I don't see how your proposal would work if we're accepting all signals of all amplitudes and all frequencies from all directions and all distances. That situation doesn't apply to equipment we launched ourselves. As for LPI radars, they DO play around with the frequencies of transmission. I might change my mind after reading more about these technologies.

Regarding war, if the galaxy is inhabited, then the presence or absence of civilization only matters in preparing for war. You'd still want to avoid defended systems.

[Torco]

There are many other solutions to the fermi. some of them even do claim that the whole question is flawed. I do enjoy the question, it is a fun one, but if we're talking seriously, way I see it we're so far from the kinds of tech you need for interstellar civilizations that we probably don't even know what to look for. It's like an ant going "our nest grows each year, and the forest is infinitely old: why is the planet not filled with scent trails?" but the position that once you become intelligent you're gonna, on the long run, grow is not without merits. if we grant it, I'm very partial to some combination of rare earth/life and rare contact. maybe they _are_ out there but they only check on us every couple billion years. the rare life thing will immediately change when we find little fish swimming somewhere in the outer solar system. hopefully on like a TNO. of course, obligatory marxist analysis, the OP's particular formulation of the fermi assumes interstellar aliens are engaged in colonialism. ¿do they also come here to build cotton plantations? ¿do they have alien east india companies? ¿they talk on the radio, do they?

[KathTheDragon]

- Our detection range is actually small. I think you mentioned 150 ly? That's tiny compared to the galaxy, which is itself a negligible bit of matter compared to the universe.

10^4 lys were cleared by the 70's.

I think Ares means the range in which we're detectable.

[keenir]

I'd rephrase that as: in our galactic neighborhood, we found no trace of very strong signals or of weaker signals in a select band of frequencies that would be good for interstellar communication.

Yes, I wrote that somewhat loosely. We haven't found natural signals definitively pointing to artificial development either. True, artificial signals are less likely if galactic civilizations are impossible. But if galactic civilizations are impossible, then contact is also less interesting.

on the contrary - if galactic civilizations are impossible, then contact is more interesting...galactic civs aren't the only option - even if they are, then contact is definately interesting.

Regarding war, if the galaxy is inhabited, then the presence or absence of civilization only matters in preparing for war. You'd still want to avoid defended systems.

why? if you're a peaceful trader species, why would you want to avoid potential customers? ditto if you're a youngling civilization new to the interstellar medium

[Richard W]

You wouldn't identify such a signal by its amplitude. Typically these signals are implemented by some kind of phase or frequency modulation. The two types of real world system I have in mind are LPI radars and the likes of the New Horizons downlink. The latter uses very low data rates, and occupies a bandwidth about six times the data rate to carry the 'turbo-coded' signal.

No, I don't get it. Given that this is a use case where we're trying to avoid false positives, if you're unwilling to restrict the amplitude, you must do it to the frequency range in order to cut down on noise. I don't see how your proposal would work if we're accepting all signals of all amplitudes and all frequencies from all directions and all distances. That situation doesn't apply to equipment we launched ourselves. As for LPI radars, they DO play around with the frequencies of transmission. I might change my mind after reading more about these technologies.

When you wrote of identifying a signal by amplitude, I thought you had in mind looking for a temporal pattern in the amplitude.

We are considering two different detection processes. One is searching by us, who don't know the characteristics of the signal. The other is detection by the aliens of a signal whose general characteristics they do know.

The aliens could eliminate signals that were too large for the distances they are expecting the signal from, or too small to be distinguishable from noise. For detection, they might use a bank of very low bandwidth filters examining a small range of frequencies. The signal they are looking for would not just be in one filter - it might be in four or five filters with a roughly known separation. Knowing what the separation should be may drastically reduce the false alarm rate. (I can't help feeling one should be able to do better by combining the filters coherently.) Remember that we don't have that advantage.

The aliens will have the advantage of knowing what carrier frequencies are used, and what the range of Doppler shifts could be. I presume it will be small. Passive ranging of the transmission is interesting. I suppose something might be done with two vastly different frequencies so that they can exploit the difference in the refractive index of interstellar space at the two frequencies.

[rotting bones]

Yes, that's why I want to consult expert opinion on how far such techniques can help camouflage signals in practice.