Another way to think about SETI

[Puppycow]

I have heard some people in the past express the opinion that the fact that SETI has not yet found any signs of extraterrestrial life, intelligent or otherwise means that it is unlikely that there is any intelligent extraterrestrial life "nearby."

However, I have my doubts that this is really the case, and here's why:

I don't think we yet have equipment powerful enough to actually detect life on a planet that is many light-years distant. In fact, we can barely detect the planets themselves, and only then by seeing how they affect the stars around which they orbit. We don't have resolution powerful enough to directly see a planet in orbit around any star but our own. Even if there were a civilization such as our own within a radius of 100 light-years, is it likely that SETI would have detected that civilization? If Earth's doppleganger were 20 light years away, would we be able to discern radio signals emanating from the planet at that distance? Even if it were at the closest star to us, could we be sure of detecting it from 4 light years away?

Or can we safely rule out the possibility of ever finding intelligent life "nearby" using more powerful equipment based on the lack of results so far?

 

[nablator]

If Earth's doppleganger were 20 light years away, would we be able to discern radio signals emanating from the planet at that distance? Even if it were at the closest star to us, could we be sure of detecting it from 4 light years away?
?

Studies like this one (interesting detection range p.13) arxiv.org/pdf/1302.0845v1.pdf assume a hypothetical "radio loud Kardashev type II civilizations". A more modest type 0 civilization, like ours, beaming mostly low power, unfocused or low frequency radio signals would be much more difficult to detect.

There was a LOFAR study for unexplored frequencies that was completed around 2009. If they had found anything we would have heard about it by now, but I don't know how far they would detect a civilization just like ours.

 

[Aepervius]

Studies like this one (interesting detection range p.13) arxiv.org/pdf/1302.0845v1.pdf assume a hypothetical "radio loud Kardashev type II civilizations". A more modest type 0 civilization, like ours, beaming mostly low power, unfocused or low frequency radio signals would be much more difficult to detect.

There was a LOFAR study for unexplored frequencies that was completed around 2009. If they had found anything we would have heard about it by now, but I don't know how far they would detect a civilization just like ours.

Try impossible to detect. Most of our signal are gone beyond intergalactic noise level by a few AU, and nothing went beyond 1 light year except for *two* intentional high powered radio signal sent of a length of maximum 10 minutes each.

SETI would not detect us if it was directly on alpha centuri and try to hear around.

So basically all SETI can detect is somebody intentional directional high pwoered level "we are here"...

 

[godless dave]

So basically all SETI can detect is somebody intentional directional high pwoered level "we are here"...

Which, IIRC, is all it was designed to detect.

 

[Aepervius]

Which, IIRC, is all it was designed to detect.

I was answering to this "A more modest type 0 civilization, like ours, beaming mostly low power, unfocused or low frequency radio signals would be much more difficult to detect."

more difficult being an euphemism for impossible.

 

[Dinwar]

Which, IIRC, is all it was designed to detect.

That's the way I understood it, tool SETI is basically asking the question "Are they trying to contact us?" not "Are they out there?" So the objection cited in the OP ("...it is unlikely that there is any intelligent extraterrestrial life "nearby.") cannot be supported or refuted via SETI. We can tentatively conclude (though I think this is going beyond what the data support, personally) that if they exist they don't want to talk to us, but we can't conclude that they're not there.

There are ways to detect life on some planets, by the way. We can look at some of the atmospheric composition on some planets as they cross between us and their star (the difference in the radiation is a function of the atmospheric composition). If the atmosphere is fairly unstable, like our atmosphere, we can conclude that some process is maintaning it. Certain types of instability more or less require metabolism to maintain. If we find those types of instability, we can conclude that we've found life. It's basically the same process as looking for chemical trace fossils, only in space!!!!

 

[aggle-rithm]

So basically all SETI can detect is somebody intentional directional high pwoered level "we are here"...

More accurately, "we WERE here"....

 

[Dinwar]

More accurately, "we WERE here"....

Not necessarily. I mean technically, yes, they sent it before we got it--but even a hundred years isn't too long for a civilization (the culture would be different, but odds are it'd still be there). I don't follow the popular notion that intelligence is necessarily self-destructive, however, so YMMV.

 

[Puppycow]

Studies like this one (interesting detection range p.13) arxiv.org/pdf/1302.0845v1.pdf assume a hypothetical "radio loud Kardashev type II civilizations". A more modest type 0 civilization, like ours, beaming mostly low power, unfocused or low frequency radio signals would be much more difficult to detect.

There was a LOFAR study for unexplored frequencies that was completed around 2009. If they had found anything we would have heard about it by now, but I don't know how far they would detect a civilization just like ours.

Try impossible to detect. Most of our signal are gone beyond intergalactic noise level by a few AU, and nothing went beyond 1 light year except for *two* intentional high powered radio signal sent of a length of maximum 10 minutes each.

SETI would not detect us if it was directly on alpha centuri and try to hear around.

So basically all SETI can detect is somebody intentional directional high pwoered level "we are here"...

Thanks, that's what I was asking. So we would not be able to detect a civilization similar to our own then.

That's the way I understood it, tool SETI is basically asking the question "Are they trying to contact us?" not "Are they out there?" So the objection cited in the OP ("...it is unlikely that there is any intelligent extraterrestrial life "nearby.") cannot be supported or refuted via SETI. We can tentatively conclude (though I think this is going beyond what the data support, personally) that if they exist they don't want to talk to us, but we can't conclude that they're not there.

Or they don't even know that we are here. Which makes sense because we would not even be able to detect our own civilization from that distance.


If someone was intentionally trying to communicate with us, would they have to know where our planet was in relation to the sun, or is it enough to just aim the signal at the sun?

 

[Dinwar]

Or they don't even know that we are here.

True enough. At a p=0.99, our planet statistically doesn't exist even within our own solar system.

Which makes sense because we would not even be able to detect our own civilization from that distance.

Again, I'm not entirely certain that's true. We'd be able to detect the alterations to atmospheric chemistry due to our civilization, just not the radio waves. CFCs, for example, don't exist in nature.

If someone was intentionally trying to communicate with us, would they have to know where our planet was in relation to the sun, or is it enough to just aim the signal at the sun?

Depends on the beam. Personally, I'd send a concentrated beam that hits all of Earth's orbit (if possible). Once I knew I hit it, I'd focus on the planet. It's not like we can't calculate the orbit.

 

[Puppycow]

Again, I'm not entirely certain that's true. We'd be able to detect the alterations to atmospheric chemistry due to our civilization, just not the radio waves. CFCs, for example, don't exist in nature.

Doesn't that depend on being able to see the earth cross in front of the sun? Or having telescope tech that is more advanced than what we currently have. From most places in the galaxy you would not be at the right angle to see the earth pass in front of the sun.

 

[Dinwar]

Doesn't that depend on being able to see the earth cross in front of the sun?

Yes. I should have been more clear about that. There could be advances made in exploring the light given off by the planet, though (light pollution may help us find exoplanets warranting further analysis).

Or having telescope tech that is more advanced than what we currently have.

Not really. We're already doing this, so I'm really simply proposing a direction to take our current examinations. (Link is to mit.edu, by the way.)

From most places in the galaxy you would not be at the right angle to see the earth pass in front of the sun.

Right. There are limits.

 

[MinnesotaBrant]

I have heard voices telling me that this is just a mirage. That being said, I would think that any advanced race would not find it too much of a problem to cloak their activity, in fact if there are a number of races out there I would think this would be a necessity due to the scarcity of habitable worlds. In fact our planet might also be cloaked as well. (how would we even know?) to shield us from advanced races.) Alternatively, I am guessing that there is energy out there that we havent detected yet that is much faster than the speed of light. This could explain how these races could move and/or communicate across the void.

 

[LarianLeQuella]

Puppychow, you may be remembering something form that ancient and epic thread about "have they found anything yet?". Arguments went round and round, and no one seemed to listen to anyone else, stabbing the E in JREF to death. However, I reproduce this table for you:

-------------+--------------+-----------+--------+--------+-----------+
Source       | Frequency    | Bandwidth | Tsys   | EIRP   | Detection |
             | Range        |    (Br)   |(Kelvin)|        | Range (R) |
-------------+--------------+-----------+--------+--------+-----------+
AM Radio     | 530-1605 kHz |  10   kHz | 68E6   | 100 KW |  0.007 AU |
-------------+--------------+-----------+--------+--------+-----------+
FM Radio     |  88-108  MHz | 150   kHz |  430   |   5 MW |    5.4 AU |
-------------+--------------+-----------+--------+--------+-----------+
UHF TV       | 470-806  MHz |   6   MHz |  50  ? |   5 MW |    2.5 AU |
Picture      |              |           |        |        |           |
-------------+--------------+-----------+--------+--------+-----------+
UHF TV       | 470-806  MHz |   0.1  Hz |  50  ? |   5 MW |    0.3 LY |
Carrier      |              |           |        |        |           |
-------------+--------------+-----------+--------+--------+-----------+
WSR-88D      |   2.8    GHz |  0.63 MHz |  40    |  32 GW |   0.01 LY |
Weather Radar|              |           |        |        |           |
-------------+--------------+-----------+--------+--------+-----------+
Arecibo      |   2.380  GHz |  0.1   Hz |  40    |  22 TW |    720 LY |
S-Band (CW)  |              |           |        |        |           |
-------------+--------------+-----------+--------+--------+-----------+
Arecibo      |   2.380  GHz |  0.1   Hz |  40    |   1 TW |    150 LY |
S-Band (CW)  |              |           |        |        |           |
-------------+--------------+-----------+--------+--------+-----------+
Arecibo      |   2.380  GHz |  0.1   Hz |  40    |   1 GW |      5 LY |
S-Band (CW)  |              |           |        |        |           |
-------------+--------------+-----------+--------+--------+-----------+
Pioneer 10   |   2.295  GHz |  1.0   Hz |  40    | 1.6 kW |    120 AU |
Carrier      |              |           |        |        |           |
-------------+--------------+-----------+--------+--------+-----------

Just redisplayed table above for easier reading, AU = astronomical unit (avg. distance of earth to sun), LY = light year

Try impossible to detect. Most of our signal are gone beyond intergalactic noise level by a few AU, and nothing went beyond 1 light year except for *two* intentional high powered radio signal sent of a length of maximum 10 minutes each.

Actually, a few more than just two. Check out Active SETI^(WP), which has a few more than two messages sent out with the intent of catching someone's attention.

 

[mike3]

That's the way I understood it, tool SETI is basically asking the question "Are they trying to contact us?" not "Are they out there?" So the objection cited in the OP ("...it is unlikely that there is any intelligent extraterrestrial life "nearby.") cannot be supported or refuted via SETI. We can tentatively conclude (though I think this is going beyond what the data support, personally) that if they exist they don't want to talk to us, but we can't conclude that they're not there.

There are ways to detect life on some planets, by the way. We can look at some of the atmospheric composition on some planets as they cross between us and their star (the difference in the radiation is a function of the atmospheric composition). If the atmosphere is fairly unstable, like our atmosphere, we can conclude that some process is maintaning it. Certain types of instability more or less require metabolism to maintain. If we find those types of instability, we can conclude that we've found life. It's basically the same process as looking for chemical trace fossils, only in space!!!!

What would it take to do that for one of the known habitable-planet candidates? What kind of telescope tech would that require?

 

[Aepervius]

If someone was intentionally trying to communicate with us, would they have to know where our planet was in relation to the sun, or is it enough to just aim the signal at the sun?

The question is difficult to answer. If you send a certain pwoer level, that total pwoer will be dissipated over the "surface" of the ray of the signal advancing in space. Think of a vertical wall advancing in space. The energy total being spread over the wall wall. So starting at the source 1 meter surface you would have 10 kw.s , but if your surface double every 10 light year, then after 10 light year you get 5 kw.s, after 20, you get 2.5 kw.s and then after 100 light year in total you get 10/1024 less than 10 w.s etc...

If the surface is spread wide enough to cover the whole solar system, that means the signal was incredibly high powered , or near but not very parallel (very divergent) or it is very weak...

But in any case the inverse square law will get you at some point, not even counting absorption by the intergalactic medium.

 

[Aepervius]

Puppychow, you may be remembering something form that ancient and epic thread about "have they found anything yet?". Arguments went round and round, and no one seemed to listen to anyone else, stabbing the E in JREF to death. However, I reproduce this table for you:





Actually, a few more than just two. Check out Active SETI^(WP), which has a few more than two messages sent out with the intent of catching someone's attention.

Yes but compared to how long we have been here, and how much "space" there is, this is a ridiculously low number of signal. More like throwing a bottle somewhere in an ocean solar system sized and expect somebody find it.

 

[Dinwar]

What would it take to do that for one of the known habitable-planet candidates? What kind of telescope tech would that require?

Something that can detect the spectrum of the planet. We'd be essentially looking at the difference in spectrum from the star as the planet crossed it. It's technology we already have--stuff that we use on a regular basis. Obviously, the ability to "see" more detail (ie, differentiate the spectrum coming from smaller portions of the sky) is better for this, but we can still work with what we have, I think.

 

[Fudbucker]

Yes but compared to how long we have been here, and how much "space" there is, this is a ridiculously low number of signal. More like throwing a bottle somewhere in an ocean solar system sized and expect somebody find it.

That's a good way of thinking about it. Except how many people are there, looking for bottles? Perhaps there are bottle-detectors all over the ocean, just in case someone like us comes along...

 

[gsmonks]

SETI is a classic case of the defective human brain.

The basis of the whole entire project is anthropomorphic. The SETI researchers are taking the approach of looking out there for ourselves. As such the project was doomed to failure from the start.

In point of fact they don't begin to know what to look for. Intelligent alien like will be . . . well . . . alien. The various media we use for communication are designed to extend and facilitate the workings of the human voice and mind, from loudspeakers to radio to the various digital formats.

The SETI format would only work if we knew what we were looking for, meaning we'd have to know how the aliens communicate (if they do at all) first.

 

[Puppycow]

SETI is a classic case of the defective human brain.

The basis of the whole entire project is anthropomorphic. The SETI researchers are taking the approach of looking out there for ourselves. As such the project was doomed to failure from the start.

In point of fact they don't begin to know what to look for. Intelligent alien like will be . . . well . . . alien. The various media we use for communication are designed to extend and facilitate the workings of the human voice and mind, from loudspeakers to radio to the various digital formats.

The SETI format would only work if we knew what we were looking for, meaning we'd have to know how the aliens communicate (if they do at all) first.

I disagree. Light waves (radio waves are a kind of light we can't see with our eyes) are the only possible means we have for gathering information about the universe outside of our own solar system. If there is another way, it is not yet known to science.

 

[coalesce]

SETI is a classic case of the defective human brain.

The basis of the whole entire project is anthropomorphic. The SETI researchers are taking the approach of looking out there for ourselves. As such the project was doomed to failure from the start.

In point of fact they don't begin to know what to look for. Intelligent alien like will be . . . well . . . alien. The various media we use for communication are designed to extend and facilitate the workings of the human voice and mind, from loudspeakers to radio to the various digital formats.

The SETI format would only work if we knew what we were looking for, meaning we'd have to know how the aliens communicate (if they do at all) first.

Well, sure it's anthropomorphic. What other life form do we have to use as a basis for communication beyond this planet than humans? Makes sense that we base it on radio because that's all we know, and the basis of trying to find something out is to use what you do know, see where it applies (or, more often, not) and then adjust your methods from.

You have to start somewhere, but sitting around speculating about how other civilizations communicate without taking the step of at least utilizing what you DO know will get you nowhere.

Michael

 

[Mark6]

It's a classic case of "looking for lost keys under the streetlamp". Do you know the keys are under the streetlamp? No. But if they are anywhere else, you won't find them at all, so might as well look in one place where you have a chance.

 

[McHrozni]

SETI is a classic case of the defective human brain.

The basis of the whole entire project is anthropomorphic. The SETI researchers are taking the approach of looking out there for ourselves. As such the project was doomed to failure from the start.

In point of fact they don't begin to know what to look for. Intelligent alien like will be . . . well . . . alien. The various media we use for communication are designed to extend and facilitate the workings of the human voice and mind, from loudspeakers to radio to the various digital formats.

The SETI format would only work if we knew what we were looking for, meaning we'd have to know how the aliens communicate (if they do at all) first.

You have it the other way around.

The only way we know that we could detect far away alien life is the methods employed by SETI. If they communicate only by loudspeakers, we have is no possibility of detecting them anyway. Physics is not anthropomorphic, assuming laws of physics apply to the whole universe (a reasonable, but not certain assumption) aliens would experience the exact same phenomena and have the exact same array of physical laws, constants and interactions to work with. It's only reasonable to assume their technology will work in compatible ways to ours.

By the way, "digital format" not a communication method, but an encoding method, for transmission or storage of information. Wi-fi is a form of radio, and optic cables are in their basics little different from using a flashlight and Morse code. The encoding could be completely alien, and yet should still be recognizable as information from the background.

McHrozni