Opposition to Active SETI is sunk because of one thing.....

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Strelnikov
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Opposition to Active SETI is sunk because of one thing.....

Post by Strelnikov » Sun Apr 29, 2018 10:45 pm

.....Radar. We have been firing radar waves at differing frequencies and intensities into the sky for decades, and what didn't hit clouds or aircraft or satellites is now beaming out into the cosmos. Certainly it sends no message, but it is a signal of consistent strength in whichever band a transmitter was running on. That it slowly went up frequency into the microwave band might be intriguing to an alien species.
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Re: Opposition to Active SETI is sunk because of one thing..

Post by The End » Mon Apr 30, 2018 7:14 am

The greatest fear would be that the aliens will do to us what Europeans did to the Native Americans. In which case, do we really need to be broadcasting our existence? :ugeek:
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Re: Opposition to Active SETI is sunk because of one thing..

Post by Strelnikov » Mon Apr 30, 2018 8:49 am

The End wrote:The greatest fear would be that the aliens will do to us what Europeans did to the Native Americans. In which case, do we really need to be broadcasting our existence? :ugeek:


That was the fear of the dearly departed Stephen Hawking. My point is, we have already been broadcasting into the Universe for a long time both through radar and AM/VHF/UHF radio and television. The "damage" is done; thanks to things like Project Diana (where radar was bounced off the moon in 1946) and a decade-plus of high-power military moonbounce communication, signals from fifty-sixty years ago are still spiraling out into the void.
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Re: Opposition to Active SETI is sunk because of one thing..

Post by CrowsNest » Mon Apr 30, 2018 4:30 pm

The End wrote:The greatest fear would be that the aliens will do to us what Europeans did to the Native Americans. In which case, do we really need to be broadcasting our existence? :ugeek:
Mass fatalities due to alien smallpox seems like a fair price for access to faster than light space travel or even teleportation devices....plus, alien Netflix has to be way cooler, right?

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Re: Opposition to Active SETI is sunk because of one thing..

Post by ericbarbour » Tue May 01, 2018 6:29 am

Strelnikov wrote:That was the fear of the dearly departed Stephen Hawking. My point is, we have already been broadcasting into the Universe for a long time both through radar and AM/VHF/UHF radio and television. The "damage" is done; thanks to things like Project Diana (where radar was bounced off the moon in 1946) and a decade-plus of high-power military moonbounce communication, signals from fifty-sixty years ago are still spiraling out into the void.

Um, I'm not an expert on radio astronomy, but you have to realize how far apart stars and their solar systems are from each other. When a radio signal is transmitted, it is usually more-or-less omnidirectional (or at least cardioid) once it gets out of the planet's atmosphere. Radar and microwave signals from a parabolic dish antenna are highly directional when they start, but begin to spread out quickly. The problem is that its intensity declines as the square of the distance. Even if you had a gigawatt transmitter (which has never existed) running 24/7 into a highly directional antenna, by the time the signal reached the nearest star (Proxima Centauri, 4.3 light years or 25.8 trillion miles away), it would be measured in the yoctowatt range, probably less than a jansky (look it up). It would be DAMN weak. Even if you used a relatively quiet frequency band in the "microwave window", like the usual 1420 MHz hydrogen line, there's still so much background noise it's difficult to assure detection. And this is only if you're TRYING to be detected.

http://www.setileague.org/general/waterhol.htm

I could show the math if you want. Proxima Centauri is 25.8 trillion miles, or 4.15 x 10^13 kilometers. If the transmitter was emitting a signal of 1 gigawatt/sq meter (and I'm not sure that's even physically possible) with a rather narrow spectrum bandwidth of 100 Hz, the signal arriving there would be something like 5.8 x 10^-27 watts/m squared. That is in the millijansky range. ANY kind of natural or nearby artificial signal source in a nearby frequency range will probably drown it out. Even the best microwave front ends aren't perfect "brickwall" filters. Stars and other astronomical radio sources transmit radio signals that are observed on earth in the hundreds or thousands of janskys, depending on their distance, brightness and other things.

The "WOW" signal from 1977 is still a total mystery. No information, just a single powerful carrier that disappeared quickly and was never seen again. Astronomers are going to argue about it for decades to come. It's useless until it is observed again and again on other telescopes. And it doesn't help that radio telescope time is fought over by scientists from all over the world; most of them don't give a shit about detecting alien civilizations. They tend to be like artists; egomaniacs with "ideas" they want to test. Personally I'm in favor of punching scientists in the mouth when they get too shrieky. No one does it often enough. (Remember Mathsci?)

This paper goes into great detail on the "probability" of detecting a signal. It depends on a lot of unknown factors, but it isn't really very encouraging.

https://arxiv.org/ftp/arxiv/papers/0707/0707.0011.pdf

Here's another paper, about intentional interstellar two-way communications. Also not encouraging. It seriously proposes communicating via neutrinos. How the hell do you generate large amounts of neutrinos on a spacecraft? The receiver they proposed is a "single crystal of absolutely pure cobalt-60, weighing about 9 tons (a cubic meter in volume) and maintained at a constant cryogenic temperature of 0.01 K." Good luck with that!

https://www.academia.edu/2086485/Inters ... Spacecraft

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Re: Opposition to Active SETI is sunk because of one thing..

Post by Strelnikov » Thu May 03, 2018 12:27 am

ericbarbour wrote:
Strelnikov wrote:That was the fear of the dearly departed Stephen Hawking. My point is, we have already been broadcasting into the Universe for a long time both through radar and AM/VHF/UHF radio and television. The "damage" is done; thanks to things like Project Diana (where radar was bounced off the moon in 1946) and a decade-plus of high-power military moonbounce communication, signals from fifty-sixty years ago are still spiraling out into the void.

Um, I'm not an expert on radio astronomy, but you have to realize how far apart stars and their solar systems are from each other. When a radio signal is transmitted, it is usually more-or-less omnidirectional (or at least cardioid) once it gets out of the planet's atmosphere. Radar and microwave signals from a parabolic dish antenna are highly directional when they start, but begin to spread out quickly. The problem is that its intensity declines as the square of the distance. Even if you had a gigawatt transmitter (which has never existed) running 24/7 into a highly directional antenna, by the time the signal reached the nearest star (Proxima Centauri, 4.3 light years or 25.8 trillion miles away), it would be measured in the yoctowatt range, probably less than a jansky (look it up). It would be DAMN weak. Even if you used a relatively quiet frequency band in the "microwave window", like the usual 1420 MHz hydrogen line, there's still so much background noise it's difficult to assure detection. And this is only if you're TRYING to be detected.

http://www.setileague.org/general/waterhol.htm

I could show the math if you want. Proxima Centauri is 25.8 trillion miles, or 4.15 x 10^13 kilometers. If the transmitter was emitting a signal of 1 gigawatt/sq meter (and I'm not sure that's even physically possible) with a rather narrow spectrum bandwidth of 100 Hz, the signal arriving there would be something like 5.8 x 10^-27 watts/m squared. That is in the millijansky range. ANY kind of natural or nearby artificial signal source in a nearby frequency range will probably drown it out. Even the best microwave front ends aren't perfect "brickwall" filters. Stars and other astronomical radio sources transmit radio signals that are observed on earth in the hundreds or thousands of janskys, depending on their distance, brightness and other things.

The "WOW" signal from 1977 is still a total mystery. No information, just a single powerful carrier that disappeared quickly and was never seen again. Astronomers are going to argue about it for decades to come. It's useless until it is observed again and again on other telescopes. And it doesn't help that radio telescope time is fought over by scientists from all over the world; most of them don't give a shit about detecting alien civilizations. They tend to be like artists; egomaniacs with "ideas" they want to test. Personally I'm in favor of punching scientists in the mouth when they get too shrieky. No one does it often enough. (Remember Mathsci?)

This paper goes into great detail on the "probability" of detecting a signal. It depends on a lot of unknown factors, but it isn't really very encouraging.

https://arxiv.org/ftp/arxiv/papers/0707/0707.0011.pdf

Here's another paper, about intentional interstellar two-way communications. Also not encouraging. It seriously proposes communicating via neutrinos. How the hell do you generate large amounts of neutrinos on a spacecraft? The receiver they proposed is a "single crystal of absolutely pure cobalt-60, weighing about 9 tons (a cubic meter in volume) and maintained at a constant cryogenic temperature of 0.01 K." Good luck with that!

https://www.academia.edu/2086485/Inters ... Spacecraft


Everything you wrote is absolutely on the money, but the fear of Active SETI is built on the idea that some alien megacivilisation has really good RA antennas that are probably automated and that these robot antennas are scanning the universe looking for signals, and that when We Are Found Out, THEY will show up with technology beyond our imagination and everything we know will be shattered. I think that the opposite would happen, that the megacivilisation would avoid us as being too primitive, or that it might send a probe to communicate by radio from within the solar system, but we would never see what the aliens look like*, because that might be too much to take in. All of this is conjectural at this point.....my source for the anti-ASETI people was this Jacobin article from three years ago. In February 2015, an open letter against ASETI (which is also called "Messaging to Extraterrestrial Intelligence") was drafted and 28 people signed it, including Elon "Rocketboy" Musk, George Dyson the science writer, and sci-fi writers David Brin and Paul Davies. The drafter was Douglas Vakoch of the SETI Institute. I see a lot of shallowly-buried guilt about how Western Europe got involved with the African slave trade and brought it to America, where the Native population was nearly wiped out by the successor American government, and that the guilt has been dumped on space creatures that may or may not exist.

_________________

* That was one of my problems with UFO aliens, that they seemed to mostly be humanoid and have the ability to tolerate oxygen and Earth gravity, unless most of them were some sort of advanced biomechanical fakes and the entire Close Encounter issue is a test of some sort; John Keel thought that way, but then he thought the entire phenomena was another dimension screwing with ours purely for kicks.
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