WFJ wrote: ↑Mon Oct 25, 2021 10:19 pm
Millennie Al wrote: ↑Mon Oct 25, 2021 10:09 pm
JQH wrote: ↑Mon Oct 25, 2021 9:13 am
The Fermi Paradox is not just the lack of space travelling aliens- they're not transmitting (by any means we can detect) either;
The Great Silence
That's a lot easier to explain. If you consider transmissions from Earth, in a fairly short period we have gone from transmitting very simple, easily recognised and decoded signals, to much more complex signals. More and more connections are encrypted, which makes the data seem random. And the next major advance in security may be a way of defeating traffic analysis, which might make it impossile to even detect that there is a signal. If all civilisations follow this path, the amount of detectable signal may be negligible.
"Random" radio/microwave transmissions would not appear random to when viewed from across the galaxy. They would be a clear signal, even if the information encoded in the signal would not be understandable. They would however be incredibly weak and coming from a tiny angle of the sky.
Spread spectrum, digital encoding and wider use of the spectrum is making signals pretty hard to detect against the thermal and non-thermal background, as they are less distinguishable from thermal noise when integrated together than less dense analog signals.
Remember that any signal from Earth when viewed from as close as Alpha Centauri is embedded in the background radiation from Jupiter and the Sun, among other sources. Jupiter's radio emissions total over 100 GW, and are highly variable. That should be compared with the average power consumption of the human race, about 17 TW, most of which is not emitted as radio signals, or to total TV signal transmissions, of the order of 1 GW. Earth also has natural radio emissions in the 100 kHz range that are as bright as Jupiter's.
Additionally, the Sun has a radio brightness temperature of about 300,000 K, many times brighter than it is in the optical.
A useful paper on detectability of narrow band human signals is this one from 1978. However, digital signals are much broader band, and thus harder to detect.
https://www.jstor.org/stable/1745785