|PaulNM on 2 Mar 2017 19:47:08 -0800|
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|Re: [PLUG] "Nearby"|
On 03/02/2017 06:01 PM, JP Vossen wrote:
There's a related question which I'm totally unqualified to even consider, but yet, I will. The electromagnetic radiation (EMR) that Earth emits is an expanding spherical shell. It started when we started emitting, and is subject to attenuation per the cube/square law. How much longer are we going to emit like that? Broadcast radio & TV are, at least arguably, declining. A lot of internet is in glass fibers that don't emit much or any EMR into space. But there may be lots of other things emitting EMR I'm not thinking about. So--how much longer are we going to be emitting at detectable levels?
It's my understanding that it's been quite awhile since our standard broadcasts were going out at enough power to be detectable outside the solar system. Even before we started shifting to non-radio broadcasting, we've been reducing power output in the name of efficiency.
Also, our emissions aren't in a sphere. Most were somewhat directional, but dissipation and losing strength over time/distance.
It seems our biggest output was early-warning radar during the cold war, and even that has declined significantly. It looks like the best case scenario is a *very* close by system may be able to pick up enough noise to tell that the signal is artificial in nature, assuming they get hit with stuff from the cold war era.
Fun reading: https://what-if.xkcd.com/47/ https://briankoberlein.com/2015/02/19/e-t-phone-home/ https://www.theguardian.com/science/2010/jan/27/aliens-cant-hear-us-astronomer -- PaulNM ___________________________________________________________________________ Philadelphia Linux Users Group -- http://www.phillylinux.org Announcements - http://lists.phillylinux.org/mailman/listinfo/plug-announce General Discussion -- http://lists.phillylinux.org/mailman/listinfo/plug