<p>I've been getting interested in the Fermi Paradox discourse again, and something's been bugging me about the assumptions we could actually detect incidental radio signals from aliens, or vice versa.</p>
<p>So, I understand there's a number of variables here- but let's assume intraplanetary communications are being used. I actually believe at any sizeable distance, radio lasers would be the norm, and so we would be unlikely to see interplanetary communications given they are directional. So let's stick to the kinds of signals we would use to communicate from one end of a planet to another.</p>
<p>As radio broadcasts extend outward in space, they are subject to a loss of signal strength based on distance alone- but how far would it go before being drowned out by background radiation?</p>
<p>Like, about how far away could an alien be before the possibility of them intercepting episodes of Leave it to Beaver reaches zero? Or what's an equation that breaks down the variables, at least?</p>

CC BY-SA 4.0
2022-07-26T14:06:26.493Z
As electromagnetic waves spread out, their amplitude decreases with distance squared. I read/heard somewhere that once the amplitude is less than the Planck length, the signal effectively "stops". However, I can't find any reliable source to back this up, so I could be wrong.
Barry Carter
CC BY-SA 4.0
2022-07-26T16:53:48.213Z
I have seen other discussions about the CMB being the noise floor, and the limits of discerning signals from it.  Again, no good reference to provide.
Greg Miller
CC BY-SA 4.0
2022-07-26T19:15:29.173Z
Not sure if this is an exact duplicate, but is definitely worth reading: [When do radio and tv signals become indistinguishable from background noise of the universe?](https://astronomy.stackexchange.com/q/33939/23786).
Greg Burghardt
CC BY-SA 4.0
2022-07-27T07:59:19.767Z
Does this answer your question? [When do radio and tv signals become indistinguishable from background noise of the universe?](https://astronomy.stackexchange.com/questions/33939/when-do-radio-and-tv-signals-become-indistinguishable-from-background-noise-of-t) see also https://astronomy.stackexchange.com/questions/18059/can-seti-certify-whether-or-not-proxima-b-is-inhabited-by-beings-using-electroma and https://astronomy.stackexchange.com/questions/8146/how-far-away-could-we-detect-that-earth-has-life
ProfRob
<radio-astronomy><radio-telescope><fermi-paradox>
What is the maximum distance we could detect incidental radio signals from aliens?
Logan Shaw
# What is the maximum distance we could detect incidental radio signals from aliens?

(Asked by: username_0 on 2022-07-26)

I've been getting interested in the Fermi Paradox discourse again, and something's been bugging me about the assumptions we could actually detect incidental radio signals from aliens, or vice versa.

So, I understand there's a number of variables here- but let's assume intraplanetary communications are being used. I actually believe at any sizeable distance, radio lasers would be the norm, and so we would be unlikely to see interplanetary communications given they are directional. So let's stick to the kinds of signals we would use to communicate from one end of a planet to another.

As radio broadcasts extend outward in space, they are subject to a loss of signal strength based on distance alone- but how far would it go before being drowned out by background radiation?

Like, about how far away could an alien be before the possibility of them intercepting episodes of Leave it to Beaver reaches zero? Or what's an equation that breaks down the variables, at least?

**Tags:** radio-astronomy, radio-telescope, fermi-paradox

> **Comments:**
> **username_1**: As electromagnetic waves spread out, their amplitude decreases with distance squared. I read/heard somewhere that once the amplitude is less than the Planck length, the signal effectively "stops". However, I can't find any reliable source to back this up, so I could be wrong.  
> **username_2**: I have seen other discussions about the CMB being the noise floor, and the limits of discerning signals from it.  Again, no good reference to provide.  
> **username_3**: Not sure if this is an exact duplicate, but is definitely worth reading: [When do radio and tv signals become indistinguishable from background noise of the universe?](https://astronomy.stackexchange.com/q/33939/23786).  
> **username_4**: Does this answer your question? [When do radio and tv signals become indistinguishable from background noise of the universe?](https://astronomy.stackexchange.com/questions/33939/when-do-radio-and-tv-signals-become-indistinguishable-from-background-noise-of-t) see also https://astronomy.stackexchange.com/questions/18059/can-seti-certify-whether-or-not-proxima-b-is-inhabited-by-beings-using-electroma and https://astronomy.stackexchange.com/questions/8146/how-far-away-could-we-detect-that-earth-has-life  

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## 0 answers

