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About SETI. Please correct me but I'm under assumption that the signals they're looking for are basically analog radio waves similar to our old TV and radio bro

by miika 5y ago

About SETI. Please correct me but I'm under assumption that the signals they're looking for are basically analog radio waves similar to our old TV and radio broadcasts? But digital communication, especially when encrypted, would completely blend with the background noise.. right? Could we even detect our own modern signals with SETI? And communication based on quantum entanglement etc way more advanced stuff SETI would completely miss + we don't even know all the different ways they could be communicating. Our ideas are reflecting our on state of technology, right?

pajko 5y ago
> But digital communication, especially when encrypted, would completely blend with the background noise.. right? Not exactly. The important part is that how the signal is modulated, or more precisely, whether the spread spectrum of the signal has been modulated or not. Every signal modulation has a unique power spectral density graph, disambiguating it from random noise. However spread spectrum modulation gives a twist on top of that. Frequency hopping (FHSS) slices the transmission in smaller fragments, transmitting them in order at pseudorandom frequencies. Spectral diagram would show a bunch of spikes, which still could be identified as the output of some civilization or burst transmissions of a star. For example, Bluetooth uses this technique. https://www.youtube.com/watch?v=6qNWQxRKoss https://www.youtube.com/watch?v=6qNWQxRKoss Direct-sequence spread spectrum (DSSS) distributes the energy of a channel on a wider bandwidth, reducing energy to background noise level, making it hard to disambiguate from random noise, unless you know where to look at and what to look for. Used by older (802.11b) Wifi, GSM, ... Newer (g, n, ac, ...) Wifi uses OFDM signal modulation, which again has its characteristic spectral diagram.
yyyk 5y ago
SETI could have never worked as it presents itself. Our digital signals are too weak for interplanetary distance. Even our analog signals are too weak unless amplified and directly broadcasted at an intersteller target. If aliens bothered to directly contact us, they could easily broadcast strongly enough that SETI wouldn't be needed at all, and why wouldn't they? (Even if they didn't, military systems would have picked up the signal before SETI did). OTOH, SETI is very good at what it's actually doing, redirecting resources to radioastronomy.

by miika 5y ago

pajko 5y ago

> But digital communication, especially when encrypted, would completely blend with the background noise.. right? Not exactly. The important part is that how the signal is modulated, or more precisely, whether the spread spectrum of the signal has been modulated or not. Every signal modulation has a unique power spectral density graph, disambiguating it from random noise. However spread spectrum modulation gives a twist on top of that. Frequency hopping (FHSS) slices the transmission in smaller fragments, transmitting them in order at pseudorandom frequencies. Spectral diagram would show a bunch of spikes, which still could be identified as the output of some civilization or burst transmissions of a star. For example, Bluetooth uses this technique. https://www.youtube.com/watch?v=6qNWQxRKoss https://www.youtube.com/watch?v=6qNWQxRKoss Direct-sequence spread spectrum (DSSS) distributes the energy of a channel on a wider bandwidth, reducing energy to background noise level, making it hard to disambiguate from random noise, unless you know where to look at and what to look for. Used by older (802.11b) Wifi, GSM, ... Newer (g, n, ac, ...) Wifi uses OFDM signal modulation, which again has its characteristic spectral diagram.

yyyk 5y ago

SETI could have never worked as it presents itself. Our digital signals are too weak for interplanetary distance. Even our analog signals are too weak unless amplified and directly broadcasted at an intersteller target. If aliens bothered to directly contact us, they could easily broadcast strongly enough that SETI wouldn't be needed at all, and why wouldn't they? (Even if they didn't, military systems would have picked up the signal before SETI did). OTOH, SETI is very good at what it's actually doing, redirecting resources to radioastronomy.