On Sunday, February 4, 2018 at 8:40:48 AM UTC-6, agrays...@gmail.com wrote:
> On Sunday, February 4, 2018 at 12:15:16 AM UTC-7, agrays...@gmail.com 
> wrote:
>> On Saturday, February 3, 2018 at 7:45:16 PM UTC-7, John Clark wrote:
>> *I'll let LC reply. He was pretty sure of his conclusion, and as I recall 
>> there were no dissenters on another MB having some physicists as 
>> contributors including Brent.  LC might have been referring to a particular 
>> wave length used by SETI (the "water hole"?). AG*
> *As I recall, LC was referring to radio waves emanating from radio 
> broadcasts. In any event, there some obvious possibilities why we have not 
> made EM contact with extraterrestrials. Maybe the Milky Way is too young 
> for a galactic civilization to come into existence, and/or, advanced 
> civilizations might decide NOT to broadcast due to the possible existence 
> of predator species.  As for your definitive negative evaluation of Roswell 
> having been an alien contact, I fail to see any basis for your conclusion 
> other than bias. AG *

There have been transmissions by Arecibo. The famous one that Sagan talked 
about was a transmission to a globular cluster. Of course a globular 
cluster is a terrible place to expect life, as the stars are all PopII with 
few heavy elements. The Arecibo can collimate radiation and that reduces 
the 1/r^2 attenuation. I am not sure if it will transmit anywhere in the 
galaxy. If I recall one reason for aiming at a globular cluster is these 
are most often off the plane of the Milky Way and your signal gets out of 
the ionized "muck" quickly. 

Our ordinary radio transmissions are not going to be decipherable beyond 
about 10 light years. An observer on alpha Centuri or Tau Ceti might be 
able to pick up some stuff. The broadcast and detection of radio signals 
between collectives of intelligent life on different planets I think will 
have to be due to deliberate actions. If we receive something it will be 
intentional, and if we want to hail putative ETIs out there we have to be 
constantly sending collimated high powered radio signals. 


>> The old 300 meter Arecibo telescope could communicate with a similar 
>>> telescope anywhere in the galaxy, and the Chinese just made a 500 meter 
>>> one. We've only been at this for a century and it's been 13.8 billion years 
>>> since the Big Bang but we have not heard  a peep from anyone. Zero zilch 
>>> nada goose egg. There must be a filter that prevents a Star Trek galaxy 
>>> from occurring, the only question is if that filter is in our past of in 
>>> our future.    

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