This tends to be supported by the fact no one has received any radiosignals from "them."

Radio signals radiate out in a spherical shell. Presuming (because we have no evidence either way) that advanced civilizations would have (if they formed like they did on Earth) started broadcasting 200-500 years ago, and given the number of stars in the vicinity, we'd have picked up something by now. We haven't.

https://www.cloudynights.com/article...-paradox-r3162

On Mon, 17 Sep 2018 15:14:02 -0700 (PDT), RichA
wrote:

Radio signals radiate out in a spherical shell. Presuming (because we have no evidence either way) that advanced civilizations would have (if they formed like they did on Earth) started broadcasting 200-500 years ago, and given the number of stars in the vicinity, we'd have picked up something by now. We haven't.

https://www.cloudynights.com/article...-paradox-r3162

We wouldn't expect to be able to detect spherically radiated radio
signals, unless they were from the very nearest stars (and maybe not
even those). And there is little reason to think that alien species
would be broadcasting high power directed beams our way. Our failure
to detect anything tells us almost nothing (which is also the
conclusion of the referenced paper).

On 17/09/2018 23:14, RichA wrote:
Radio signals radiate out in a spherical shell. Presuming (because
we have no evidence either way) that advanced civilizations would
have (if they formed like they did on Earth) started broadcasting
200-500 years ago, and given the number of stars in the vicinity,
we'd have picked up something by now. We haven't.

https://www.cloudynights.com/article...-paradox-r3162

An emerging civilisation is only likely to be radio bright and making
obviously non thermal modulated signal emissions for a relatively short
period of time from the point where they have high power transmitters to
the point where they adopt digital techniques and streaming.

That window for the Earth was narrower than 100 years. We occasionally
send powerful beamed emissions in random directions that Arecibo can
point at and illuminate chunks of sky whilst doing TDR imaging of near
Earth asteroids so every now and then the odd pulse still goes out.


There may be someone sat on Trappist-1 40ly away watching the Apollo
missions on our old terrestrial TV transmissions but it will be another
40 years before they could reply even if they decided to do so.



http://earthsky.org/space/3-potentia...ght-years-away


--
Regards,
Martin Brown

Under-developed adults looking for aliens with superior intelligence is a sort of an answer to what is in front of them each day - something greater than themselves in time and geometry that makes their life possible. Anyone would think they are looking for image mirrors of themselves among the planets that move around the stars !.

On Tuesday, 18 September 2018 05:05:39 UTC-4, Martin Brown wrote:
On 17/09/2018 23:14, RichA wrote:
Radio signals radiate out in a spherical shell. Presuming (because
we have no evidence either way) that advanced civilizations would
have (if they formed like they did on Earth) started broadcasting
200-500 years ago, and given the number of stars in the vicinity,
we'd have picked up something by now. We haven't.

https://www.cloudynights.com/article...-paradox-r3162

An emerging civilisation is only likely to be radio bright and making
obviously non thermal modulated signal emissions for a relatively short
period of time from the point where they have high power transmitters to
the point where they adopt digital techniques and streaming.

That window for the Earth was narrower than 100 years.

That's assuming they don't purposefully continue to radiate to make contact. There was a radio broadcaster using 500,000 watts in the 1930's at about 900KHz. Not sure what the power and frequency would be 4-20LY out.

On 20/09/2018 02:23, RichA wrote:
On Tuesday, 18 September 2018 05:05:39 UTC-4, Martin Brown wrote:
On 17/09/2018 23:14, RichA wrote:
Radio signals radiate out in a spherical shell. Presuming
(because we have no evidence either way) that advanced
civilizations would have (if they formed like they did on Earth)
started broadcasting 200-500 years ago, and given the number of
stars in the vicinity, we'd have picked up something by now. We
haven't.

https://www.cloudynights.com/article...-paradox-r3162



An emerging civilisation is only likely to be radio bright and making
obviously non thermal modulated signal emissions for a relatively
short period of time from the point where they have high power
transmitters to the point where they adopt digital techniques and
streaming.

That window for the Earth was narrower than 100 years.

That's assuming they don't purposefully continue to radiate to make
contact.

Its highly unlikely that they will. Any signals are likely to be
serendipitous high power radar beams imaging things.

There was a radio broadcaster using 500,000 watts in the
1930's at about 900KHz. Not sure what the power and frequency would
be 4-20LY out.

Same frequency give or take our orbital Doppler shift but the incident
flux would be quite small (but not necessarily undetectable). TV line
scan and frame rate would be a dead giveaway for an artificial signal.

Hence the reason the first pulsar trace recorded was marked LGM.

--
Regards,
Martin Brown