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

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