Is SETI a Silly Effort To Investigate?

[PCarr]

I don't think so. People who make this pronouncement are overlooking several things, but the most important thing they are trying to avoid is the truth that science is hard. Really hard. Doing science requires patience, humility, skepticism and a systematic approach. You do an experiment (which may take generations, especially if your funding is shoestring), and you take what you learn from that experiment and try something else. We have not come anywhere near covering the entire search space just in the radio spectrum.

I wote out my thoughts on this in more detail here:
Dream of the Open Channel: Is SETI Silly?

and here is my discussion with Seth Shostak on the topic:
The Wow! Signal Podcast: Episode 6 - Conversation with an Alien Hunter

 

[Charlie Prime]

I like the idea of SETI.

As long as it's privately funded, I support the endeavour.

For several years I ran the distributed computing program all night on all my workstations.

 

[manxman]

bet you wish now, you had run a bitcoin mining operation instead.

 

[pduchesne]

If the universe were teeming with technologically advanced life, wouldn't you expect there would already be a SETI cable channel where we could tune into Alien TV and watch broadcasts from the little green men?

At the very least, I would expect an alien race to have detected our presence and broadcast directly to us.
Can you imaging what our planet would look like from across the galaxy with all the Doppler weather radars blasting into space? Then there are the aviation radars and satellite communications.
Alien races within a radius of about 50 light years would have had time to detect our signals and send something back to us.

I still think SETI is a worthwhile effort, given that it is privately funded and the payoff for success would be huge.

 

[Charlie Prime]

At the very least, I would expect an alien race to have detected our presence and broadcast directly to us.

I think this unlikely because man-made electromagnetic radiation fades into background noise about 1 light-year out from earth.

 

[PCarr]

At the very least, I would expect an alien race to have detected our presence and broadcast directly to us.

Well now, think about it - we've only mastered microwaves for about 70 years. A round trip light time of 70- years only goes out 35 light years, which is only a few hundred stars. So, the odds are poor that we wold now be hearing from someone who has detected our radar.

 

[PCarr]

I think this unlikely because man-made electromagnetic radiation fades into background noise about 1 light-year out from earth.

Can you cite a source for that? It would Strongly depend on frequency, since the background noise vafres quite a lot with frequency, and of course the effective power with which we radiate depends upon the directionality. A radar signal from Arecibo is powerful and highly directional, so it would be detectable quite a long way away. You just have to see a signal - not demodulate it.

 

[pduchesne]

Well now, think about it - we've only mastered microwaves for about 70 years. A round trip light time of 70- years only goes out 35 light years, which is only a few hundred stars. So, the odds are poor that we wold now be hearing from someone who has detected our radar.

That's why I estimated a radius of 50 light years. I was too lazy to look up the history of radar, so I defer to your more reasoned 35 light year radius.

 

[pduchesne]

I think this unlikely because man-made electromagnetic radiation fades into background noise about 1 light-year out from earth.

Well, if this is true, then I want to change my answer to SETI is a waste of time. I'll have to verify it for myself though.

 

[manxman]

why anyone would think advanced races would use microwave or radiowave to communicate is beyond me, i doubt our use of either will be more than 200 years before technology moves on, i am also sure that they would have near instant communication, no matter how far they travelled.

personally i think seti is futile, as already demonstrated.

 

[Stagger Lee]

I figured folks way out in the galaxy were watching re-runs of Ralph Cramden and the gang.

 

[pduchesne]

Well, if this is true, then I want to change my answer to SETI is a waste of time. I'll have to verify it for myself though.

Crap. Charlie is essentially right. Doppler weather radars would only be detectable to about 0.01 light years, even though they have an effective power of more than 30 gigawatts. We would need an Arecibo sized antenna transmitting a terawatt of power to be seen at just 150 light years. That's one narrow, hard to find beam. That leads to the question, why would anyone send that much power into space?

 

[Charlie Prime]

Can you cite a source for that?

I apologize, but I cannot remember where I read that. Some rough calculations would confirm it.

Radio signals degrade with distance due to the "inverse square law".

Take the most powerful of man's electromagnetic transmitters, the Roumoules transmitter in France that can pump out 3,000 kilowatts. Calculate the remaining power of that signal at 1, 10, and 100 light years.

At those distances, does that signal fall below the background radio noise level of the Sun, or Big Bang?

I think it would, but I cannot perform the calculations because my math education was so poor as to border on criminal.

Next consider that the first human radio transmissions were only about 109 years ago. How many "Goldielocks Zone" planets exist within 109 light years of earth? 100? 20,000?

Now estimate how many of those planets experienced the incredible good fortune of developing a radiation shielding atmosphere and magnetosphere, had a nearby supernova to provide life-giving metals or silicates, and spawned advanced civilizations.

 

[Randall]

I think this unlikely because man-made electromagnetic radiation fades into background noise about 1 light-year out from earth.

Interesting. Where did you get this information?

 

[manxman]

I figured folks way out in the galaxy were watching re-runs of Ralph Cramden and the gang.

Crap. Charlie is essentially right. Doppler weather radars would only be detectable to about 0.01 light years, even though they have an effective power of more than 30 gigawatts. We would need an Arecibo sized antenna transmitting a terawatt of power to be seen at just 150 light years. That's one narrow, hard to find beam. That leads to the question, why would anyone send that much power into space?

i dont think 'i love lucy' will a great loss to the universe.

and the signal strength isnt as importand as the sensitivity of the reciever.

 

[pduchesne]

i dont think 'i love lucy' will a great loss to the universe.

and the signal strength isnt as importand as the sensitivity of the reciever.

If SETI provided us with the alien equivalent of 'I love lucy', would you be disappointed that aliens are as stupid as we are, or would it be one of the coolest things to happen in your lifetime? I'd go with the latter, but I'm boring like that.

 

[manxman]

if they have war films then we are toast, ya didnt reckon on that did ya.

 

[PCarr]

I apologize, but I cannot remember where I read that. Some rough calculations would confirm it.

Radio signals degrade with distance due to the "inverse square law".

Take the most powerful of man's electromagnetic transmitters, the Roumoules transmitter in France that can pump out 3,000 kilowatts. Calculate the remaining power of that signal at 1, 10, and 100 light years.

At those distances, does that signal fall below the background radio noise level of the Sun, or Big Bang?

I think it would, but I cannot perform the calculations because my math education was so poor as to border on criminal.

Next consider that the first human radio transmissions were only about 109 years ago. How many "Goldielocks Zone" planets exist within 109 light years of earth? 100? 20,000?

Now estimate how many of those planets experienced the incredible good fortune of developing a radiation shielding atmosphere and magnetosphere, had a nearby supernova to provide life-giving metals or silicates, and spawned advanced civilizations.

It's not the total power, but the Effective Isotropic Radiated Power (EIRP as we call it) that matters. That is a function of the power AND the efficiency and gain of the transmitting array. On the other end, it's the Gain/Temperature (G/T) of the receiving array, where the temperature were talking about here is "noise temperature". The important noise energy is only the noise in the narrow band you are looking for. With the right transmitter at the right frequency in a narrow band you can completely overwhelm it quite some distance away. And our civilization has only been doing stuff like this for about 70 years.

See:

[sci.astro] ET Life (Astronomy Frequently Asked Questions) (6/9)Section - F.06 How far away could we detect radio transmissions?

 

[Charlie Prime]

The important noise energy is only the noise in the narrow band you are looking for.

The chart you referenced said 750 light years was the maximum distance.

How many planets like I described above are thought to exist within 750 light years of earth?

 

[boomerang]

It's not the total power, but the Effective Isotropic Radiated Power (EIRP as we call it) that matters. That is a function of the power AND the efficiency and gain of the transmitting array. On the other end, it's the Gain/Temperature (G/T) of the receiving array, where the temperature were talking about here is "noise temperature". The important noise energy is only the noise in the narrow band you are looking for. With the right transmitter at the right frequency in a narrow band you can completely overwhelm it quite some distance away. And our civilization has only been doing stuff like this for about 70 years.

See:

[sci.astro] ET Life (Astronomy Frequently Asked Questions) (6/9)Section - F.06 How far away could we detect radio transmissions?

You obviously understand this on a deeper technical level than I do, so let me attempt to "dumb it down" a little in hopes of clarification. Radiated electromagnetic energy can be, to some extent, focused and beamed in a particular direction. One example is the ubiquitous parabolic radio dish. Perhaps The best example of which most of us know is the laser, which "spreads" only slightly as a function of distance--all relatively speaking.

Clearly detecting a signal is not so much a function of signal strength, as it is of the ratio of the signal's strength to whatever noise competes with it, whether the noise is inherent in the receiving device or arriving along with the signal. Am I close here?

Re Seti; Considering the tiny percent of overall resources it costs us, it's a fine investment. I would fault it only for its being predicated on a kind of linear thinking: That civilizations more advanced than ours will have no better means of communication than the electromagnetic spectrum. Or that they would care to be known at all. This may or may not be true. At any rate, I think our best efforts to listen are well worthwhile.