What do you think is the most likely explanation for the Fermi paradox?

[Jens]

Absolutely, we don't know for certain what we are looking for and could well be missing communication staring us right in our face. I guess we can only assume based on what we know and therefore lookout for patterns that appear to be either complex or very random. These may indicate an "unnatural" source possibly even intelligence. Unless we discover a more efficient way of long distance communication then we can only assume that ET would use the same methods as us. What else can we do?

I guess it could be a bit like someone looking for smoke signals or listening for the beating of loud drums cause that's the only way they know how to send messages long distances, not realising that the air is filled with radio signals all around them. They would likely conclude that there is no one out there just an "eerie" silence.

Yes, that’s what I think. As you say, we can look out for what seem to be unnatural sources, but of course we cannot be certain that that are not natural. But yes, it’s really the best we can do.

[Noclevername]

We now know a lot more about natural sources than we did before, of course. In that sense, it's been very fruitful to continue to look.

But whether we can tell what emission is natural is our own problem with perception, not an innate quality of communications, IMO. I think if someone's trying to send a clear signal, they'll make it as distinctively artificial as possible.

Any ETI who doesn't care about clarity or coherence to an alien mind, would probably not send out intentional messages in the first place. We'd be stuck trying to detect and interpret their accidental leakages, which easily blend into background noise.

That's all I was trying to say.

[cosmocrazy]

Either way, unless they send signals, intentionally or not, by a means that we can recognise, then we are just stabbing in the dark.

We could be just beating on our drums and sending smoke signals, completely unaware of all the signals around us.

[Noclevername]

Either way, unless they send signals, intentionally or not, by a means that we can recognise, then we are just stabbing in the dark.

We could be just beating on our drums and sending smoke signals, completely unaware of all the signals around us.

True. But as I said above, RF signals are convenient for the purpose, so we're probably going to continue unabated for the foreseeable future. As with the search for life itself, we start with what we already know works, and then branch out our efforts from there.

[Colin Robinson]

As far as alien motivations I can't say. TBD. As for humans, no, I don't believe RF communication is a passing fad. It's here to stay, as its properties make it useful for that purpose.

It's like water-based organic life; we already know it happens so it can be said self-evidently to be a reasonable basis for life. We can look for other solvents and compounds but they are purely speculative. Same with RF, it proves useful enough to be the basis for the overwhelming majority of telecommunication. Those properties are universal, so we might reasonably expect that a civilization that has enough industrial technology to go into space or search the skies for life would also put RF to use.

True. But as I said above, RF signals are convenient for the purpose, so we're probably going to continue unabated for the foreseeable future. As with the search for life itself, we start with what we already know works, and then branch out our efforts from there.

I agree (up to a point) that we have to start from what we know.

Although one thing we know from studying life on Earth is that life is diverse.

As we look for life and intelligence on other worlds, isn't it reasonable to expect still great diversity?

I'm concerned that if we focus too much on hypothetical beings that closely resemble us, either in terms of their body chemistry or in terms of their engineering, we may miss a lot of what's out there.

[Jens]

We now know a lot more about natural sources than we did before, of course. In that sense, it's been very fruitful to continue to look.

But whether we can tell what emission is natural is our own problem with perception, not an innate quality of communications, IMO. I think if someone's trying to send a clear signal, they'll make it as distinctively artificial as possible.

Any ETI who doesn't care about clarity or coherence to an alien mind, would probably not send out intentional messages in the first place. We'd be stuck trying to detect and interpret their accidental leakages, which easily blend into background noise.

That's all I was trying to say.

I fully agree that ETI would likely try to send a signal that could be logically deciphered makes sense. I assume that they would, and that we do. I think what Colin was saying is, what if for some reason, they are unable to understand it, or conversely, that someone is broadcasting but that for some reason, due to technological limitations or something else, we are not able to understand it? I am not convinced that would happen, but I'm not enough of an expert to be able to rule that out, especially since we have received what we was a clear signal, so we don't have any data points. So I don't think that I am disagreeing with you.

[cosmocrazy]

I think we all agree that RF signals are, at least at this point, the logical signal to try to detect in regards to long distance communication. We know enough about this type of communication, and how it is likely to be generated to have a good go at deciphering a signal, should it be strong enough. We can, to some degree, also determine if it comes from a natural source, since we have quite a lot of data on how RF signals are generated naturally. We ourselves tend to use "unnatural" band widths to use as communication, so I guess it is logical to assume ET would do similar for the same reasons we do.

If RF signalling is the most efficient and economical means of long distance communication then its easy to see how ET may adopt the same techniques and come to a similar solution. Based on this assumption what else can we do? We can only use what we know and speculate/assume on what we don't. How would it even be possible to try and detect anything else? Until of if we discover another means that supersedes RF then we are limited to our search for technological ET.

We could be simply listening for the beat of drums, not realising that drums were never used or abolished a long time ago. But we know of no other useful means of communication, so all we can do for now is carry on beating ourselves, and listening in hope.

[Noclevername]

We can only use what we know and speculate/assume on what we don't. How would it even be possible to try and detect anything else? Until of if we discover another means that supersedes RF then we are limited to our search for technological ET.

We could be simply listening for the beat of drums, not realising that drums were never used or abolished a long time ago. But we know of no other useful means of communication, so all we can do for now is carry on beating ourselves, and listening in hope.

We do try other observational methods, to search for intelligence. We recently took a look at the data to try to find a Kardashev III galaxy of Dyson Spheres, as unlikely as we think such a thing may be. So radio is not our only option as far as looking for potential evidence of intelligence.

[Tom Mazanec]

cosmocrazy:
How about laser communication?

[Colin Robinson]

We do try other observational methods, to search for intelligence. We recently took a look at the data to try to find a Kardashev III galaxy of Dyson Spheres, as unlikely as we think such a thing may be. So radio is not our only option as far as looking for potential evidence of intelligence.

What we seem to be looking for is evidence of industrial revolutions...

[Noclevername]

What we seem to be looking for is evidence of industrial revolutions...

Well, yes, all the searches we've performed have looked for specific technical applications, which would require tool use as well as some degree of creative intellect. I don't know if there is any way to search for any other forms of intelligence, though.

[Colin Robinson]

Well, yes, all the searches we've performed have looked for specific technical applications, which would require tool use as well as some degree of creative intellect. I don't know if there is any way to search for any other forms of intelligence, though.

Thing is, the past two centuries on Earth show that industrial technology changes fast. Do we really know where it's going? How much idea do we really have of what technologies humans will be using in a hundred years, or a thousand years?

I know there are theories, including Dyson Spheres. But theorising and knowing are 2 different things, surely?

Do we know which (if any) features of current technology will be conserved for a respectable fraction of the life of a planet, and which features are in the blink-and-you'll-miss-it category?

[Noclevername]

Thing is, the past two centuries on Earth show that industrial technology changes fast. Do we really know where it's going? How much idea do we really have of what technologies humans will be using in a hundred years, or a thousand years?

I know there are theories, including Dyson Spheres. But theorising and knowing are 2 different things, surely?

Do we know which (if any) features of current technology will be conserved for a respectable fraction of the life of a planet, and which features are in the blink-and-you'll-miss-it category?

It's not about certainty; if we knew these answers in advance, we'd know exactly what to look for. It's simply a set of search parameters that are within our current capacity. We test for the testable: EM emissions and patterns that can be seen over light-years. How else could we look for an intelligent civilization?

[Colin Robinson]

It's not about certainty; if we knew these answers in advance, we'd know exactly what to look for. It's simply a set of search parameters that are within our current capacity. We test for the testable: EM emissions and patterns that can be seen over light-years. How else could we look for an intelligent civilization?

I'd suggest that the first step is to look for life in general, including microbial life.

When we know a bit more about how widespread or otherwise life is, and how evolution and eco-systems work on different worlds, we'll then be in a better position to develop and test theories about intelligent life.

[Noclevername]

I'd suggest that the first step is to look for life in general, including microbial life.

When we know a bit more about how widespread or otherwise life is, and how evolution and eco-systems work on different worlds, we'll then be in a better position to develop and test theories about intelligent life.

We can do both, you know.

But technological societies that emit energy would likely be much more detectable over interstellar distances than a planet of microbes. So we tend to pick the low hanging fruit first.

[Colin Robinson]

We can do both, you know.

But technological societies that emit energy would likely be much more detectable over interstellar distances than a planet of microbes. So we tend to pick the low hanging fruit first.

But...

Populations of ET microbes
* may be at interplanetary distances not interstellar distances
* are comparable (if they exist) to what Earth has had for billions of years
* based on Earth experience, can have easily detectable effects on the chemistry of their environment

ET technological societies
* are not expected in our own Solar System even by the most optimistic SETI advocates
* are comparable to something that has existed on Earth for a couple of centuries, and is changing fast
* Earth therefore provides no model for how a technological society may develop over time spans long than that

Which, then, is the "low hanging fruit"?

[Noclevername]

Which, then, is the "low hanging fruit"?

As I said above, those that emit energy visible over interstellar distances.

* based on Earth experience, can have easily detectable effects on the chemistry of their environment

Can but not must. Earth has had billions-year stretches of not being obvious by chemistry.

* may be at interplanetary distances not interstellar distances

If such life were here it can't be "obvious" as you put it.

* are comparable (if they exist) to what Earth has had for billions of years

Might be, as we speculate for the ease of searching.

ET technological societies
* are not expected in our own Solar System even by the most optimistic SETI advocates

Good thing no one's looking in our Solar System for technological societies, then.

* Earth therefore provides no model for how a technological society may develop over time spans long than that

It's the closest thing we've got. What alternative would be feasible as a marker of intelligence?

[cosmocrazy]

We do try other observational methods, to search for intelligence. We recently took a look at the data to try to find a Kardashev III galaxy of Dyson Spheres, as unlikely as we think such a thing may be. So radio is not our only option as far as looking for potential evidence of intelligence.

I was only considering "communication" in my post so based on that context.

[cosmocrazy]

cosmocrazy:
How about laser communication?

Maybe, though my minimal understanding is that even this has its limits and currently more difficult to detect unless a signal was directed straight at us?

[Noclevername]

I was only considering "communication" in my post so based on that context.

So, EM spectrum. At present that's about all we can try. We are barely in our infancy at even detecting things like gravity waves, which in any case would be enormously inefficient for communications purposes.

[Colin Robinson]

If such life were here it can't be "obvious" as you put it.

"Obvious" is not the way I'd put it.

What I am saying, is that microbial populations can have effects which you don't need a microscope to detect. In terms of Earth examples, I'm not thinking only of oxygen levels, but also of nitrogen fixation and algal blooms.

Are there signs of large-scale microbial activity elsewhere in the solar system?

Well, Venus has extensive dark patches in its clouds which change over time. They absorb ultraviolet light and are chemically different from their surroundings. We don't yet know what causes them, but microbial activity is a hypothesis.

What alternative would be feasible as a marker of intelligence?

I'm advocating for a broader search for biomarkers, not a narrow search for markers of intelligence.

[Noclevername]

"Obvious" is not the way I'd put it.

Easily detectable, then.

* based on Earth experience, can have easily detectable effects on the chemistry of their environment

What I am saying, is that microbial populations can have effects which you don't need a microscope to detect. In terms of Earth examples, I'm not thinking only of oxygen levels, but also of nitrogen fixation and algal blooms.

Are there signs of large-scale microbial activity elsewhere in the solar system?

Well, Venus has extensive dark patches in its clouds which change over time. They absorb ultraviolet light and are chemically different from their surroundings. We don't yet know what causes them, but microbial activity is a hypothesis.

I personally don't think we'll find life here in the Solar System, though we should still keep an eye out for it. We have seen no unequivocal supporting evidence. And certainly we have seen nothing at all that indicates any Solar System intelligence or complex life.

I'm advocating for a broader search for biomarkers, not a narrow search for markers of intelligence.

As I already pointed out, we do multiple kinds of searches and analysis already, and will probably continue to. Nothing makes those approaches mutually exclusive or limits us to one idea. But the exchange of recent posts above was about intelligence, so that's what I answered.

[Colin Robinson]

Easily detectable, then.

The dark patches in the clouds of Venus are easily detectable by ultraviolet photography. What is less easy, is establishing whether they are caused by microbial activity or something else.

I personally don't think we'll find life here in the Solar System,

I personally don't know whether we will or not.

But if we do find it — e.g. in those Venusian dark patches; or on Titan's surface, where there are indications of carbon compounds decomposing — I think we'll be surprised how easily detectable the clues were, and the extent to which they were disregarded.

As I already pointed out, we do multiple kinds of searches and analysis already, and will probably continue to. Nothing makes those approaches mutually exclusive or limits us to one idea.

That's true as far as it goes...

My basic point is that trying to answer questions about extraterrestrial intelligence right now is like trying to run before we're learned to walk.

[Noclevername]

My basic point is that trying to answer questions about extraterrestrial intelligence right now is like trying to run before we're learned to walk.

In what way? We cast a wide net in order to catch as much as we can. Radio emissions can be detected using existing technology, so why would we ignore the chance to look for a potential sign of life? We shouldn't close our eyes to a possibility just because it comes from one kind of life and not another.

[Colin Robinson]

In what way? We cast a wide net in order to catch as much as we can. Radio emissions can be detected using existing technology, so why would we ignore the chance to look for a potential sign of life? We shouldn't close our eyes to a possibility just because it comes from one kind of life and not another.

I'm saying that the net we're casting for ET life hasn't been wide enough.

For instance, we've closed our eyes to the possibility of life in the clouds of Venus because the dominant liquid there isn't something we could swim in.

I'm not opposed to listening for interstellar radio emissions. It's possible that we'll detect something that way, and if it happens it will be quite a breakthrough.

On the other hand, if we continue to not detect obviously artificial radio emissions, what will that tell us?

Will it tell us that there is no ET life out there? Will it tell us that there is no ET intelligence out there? Will it really tell us anything much at all?

[Noclevername]

I'm saying that the net we're casting for ET life hasn't been wide enough.

For instance, we've closed our eyes to the possibility of life in the clouds of Venus because the dominant liquid there isn't something we could swim in.

I'm not opposed to listening for interstellar radio emissions. It's possible that we'll detect something that way, and if it happens it will be quite a breakthrough.

I don't agree at all that we "close our eyes". We are actively looking at Venus and other worlds in our Solar System, and will continue to do so. That is not "closing our eyes".

We are rightly skeptical, as scientific analysis has to be. The standards of evidence for life are high, as they should be. In all areas of exploration and SETI. That's why WOW signals are not taken as proof of contact, nor are patches of discoloration. We verify, and until then we take things with a grain of salt; that's how it works, that's how it will always work.

On the other hand, if we continue to not detect obviously artificial radio emissions, what will that tell us?

Will it tell us that there is no ET life out there? Will it tell us that there is no ET intelligence out there? Will it really tell us anything much at all?

Your question is baffling. It sounds like you are suggesting it's futile to scan the skies for radio emissions! I'm sure this was not your intent but it sure sounds that way.

[Colin Robinson]

I don't agree at all that we "close our eyes". We are actively looking at Venus and other worlds in our Solar System, and will continue to do so. That is not "closing our eyes".

The most recent descent missions to the atmosphere and surface of Venus were in 1985.

We are rightly skeptical, as scientific analysis has to be. The standards of evidence for life are high, as they should be. In all areas of exploration and SETI. That's why WOW signals are not taken as proof of contact, nor are patches of discoloration. We verify, and until then we take things with a grain of salt; that's how it works, that's how it will always work.

The WOW signal was transient. The dark areas in the clouds of Venus are continuing, shifting features which we can investigate any time. Yet we don't...

On the other hand, if we continue to not detect obviously artificial radio emissions, what will that tell us?

Your question is baffling.

It's not only my question. Paul Davies wrote a book about it...

It sounds like you are suggesting it's futile to scan the skies for radio emissions! I'm sure this was not your intent but it sure sounds that way.

I'm pointing out that scanning for radio emissions will only detect a subset of a subset of a subset of the life that may be out there.

[cosmocrazy]

Maybe its just not exciting enough,

Finding microbial life may well be very exciting for the science community, but lets be honest, once the front page story has diminished the general public won't pay that much interest.

Yes, we as scientists or science enthusiasts like myself are likely to get excited and be very interested, simply because its a new major discovery that will begin to answer many long held questions about our universe. But unless we find ETI then the majority of folk won't care that much.

ETI search is likely to attract more funding than just looking for signs of life. Although we should be looking in all areas using all the technology we have it our disposal, no rock should go unturned, convincing the funders might be more difficult.

[Noclevername]

I'm pointing out that scanning for radio emissions will only detect a subset of a subset of a subset of the life that may be out there.

Still missing the point. It's about what we can do. We observe radio signals because we have radio telescopes. We search for what we can physically find, not what we think might be more likely or not.

As for Venus, we have been keeping an eye on it, as the recent phosphine flap shows. We may not be as fixated on it as Mars, but probes to its atmosphere are being proposed.

[Noclevername]

Although we should be looking in all areas using all the technology we have it our disposal, no rock should go unturned, convincing the funders might be more difficult.

With limits on resources we have to set priorities. Since using existing general-purpose observational equipment is cheaper than sending dedicated probes, probes will be rare.