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Not sure how many people have heard of Fermi's paradox, the famous quote is "if there are aliens out there, why haven't we heard them?" or something to that effect. The density of exo-planets now in evidence from recent observations is strongly bringing this question to the fore again.

https://en.wikipedia.org/wiki/Fermi_paradox#Overview (https://en.wikipedia.org/wiki/Fermi_paradox#Overview)
http://fermisparadox.com/ (http://fermisparadox.com/)

https://en.wikipedia.org/wiki/The_Drake_Equation (https://en.wikipedia.org/wiki/The_Drake_Equation)

It is something I've been pondering on and off for quite a while. There is a large effort SETI searching for alien signals, to date fruitlessly.

Recently, (bitcoin!) I began looking at the rate of progress of encryption of human radio communications since radio comms. began and wondered what would be effect of this for alien civilisations listening in on Earth in the future (say in 100 or 200 years time).

So, now I come to the conclusion that cryptography, or basically any technological equivalent of signal masking, is a probable solution to the Fermi paradox, and ultimately means most SETI efforts are useless or will only succeed in the very rare occasion when a civilisation goes through the "unmasked radio communication" phase soon after discovering EM radio waves, like humanity is going through at present. Basically, if cryptography proceeds at the same rate of progress as it is moving now, combined with the effect of more directed radio transmissions and less broadcast, then anybody listening towards Earth will not see anything large different from noise.

It kind of fits into the following classification but with the advance of cryptographic technology and signal masking being the major player.

"Civilizations only broadcast detectable radio signals for a brief period of time"

https://en.wikipedia.org/wiki/Fermi_paradox#Civilizations_only_broadcast_detectable_radio_signals_for_a_brief_period_of_time (https://en.wikipedia.org/wiki/Fermi_paradox#Civilizations_only_broadcast_detectable_radio_signals_for_a_brief_period_of_time)

And it may not be bad thing to have all outbound radio signals masked, who knows what nasties are waiting out there that have awoken now that our naked naive signals have been blurted out across the galaxy? Maybe it is actually mark of a sophisticated, advanced civilisations that they are unobservable (unless they choose to reveal themselves)?

Edit: tl;dr Cryptography is the Great Filter in the Drake equation

At the same time, you would think there would be a few super advanced civilizations that would setup beacons just to announce their existence.  Not on their home world, of course.

Good point. Probably safe to assume then that there are no super-advanced civs. who have set-up "here we are beacons" away from their home world, in our light cone at least.

I wonder though when a civ. would ever feel confident enough to know that once you put that beacon up there is not another bigger, badder threat now looking in your direction?

Perhaps, we should be looking for, then listening to quantum signals. Spin that idea in your charming head for a spell.

~Bruno~

You obviously haven't read "Anvil of Stars" by Greg Bear which talks about a universe in which being able to hide from other species is the single most important survival strategy because of the existence of destructive Von Neumann machines.

Seemed quite plausible :)

It does seem inevitable that von Neumann machines would eventually reach the point where finding and consuming resources overwhelms any self-restraint that might have been programmed into them. It only makes evolutionary sense.

Species 8472 comes to mind.

~Bruno~

The Fermi Paradox Song: http://www.youtube.com/watch?v=zqzMAnPKa_s

Star Trek nerd spotted. Takes one to know one.  ;)

I think this discussion is missing something.  A broadcast would not be detectable because it says "Hello, we are liitle green men" (plaintext) instead of "sfghkjrtzdfbxcvnbzd,jtsdfò" (ciphertext).  It would be detectable because it occurs on a frequency band which does not naturally occur.  Anyone scanning the sky for signals would see *a signal* whether they could understand it or not.  Suppose your country outlawed encryption - the presence of encrypted data on your computer would incriminate you (unless you can prove you're working on random number generators and need lots of random data).  Just because the government could decipher your data wouldn't mean they didn't know it was there.

http://en.wikipedia.org/wiki/Waterhole_%28radio%29

In doing a little reading, I learned that SETI@home basically only searches for intentional beacons.  One reason is that the radio-telescope used is ground-based, and the atmosphere filters out a lot of frequencies.  And another is that one of the frequencies not filtered out is that at which interstellar hydrogen resonates, making it an easy choice.

Yeah, I thought about that, that's why I said ... it's always going to be difficult to get out of an anthropocentric view of other species technologies but we can use laws of physics, as we currently understand them, to place bounds on the possible/impossible.

So imagine there is a civ. out there that wants to broadcast interstellar signals (don't know why), and wants to be able to mask that signal in some fashion. The only way to do this to avoid what you are talking about is to produce a radio broadcast signal that appears no different than noise at the RF level ... encryption, but not as we know it.

benjamindees:
SETI only looks for beacons eh ... didn't know that. What kind of civ. are they expecting to detect that would be willing to advertise itself I wonder? Someone as stupid as humans maybe?

Edit: Another thought is that human RF broadcast signals that have gone out there already, beginning in earnest around 1930ish (with strong carrier waves) will have travelled "only" 80 light years so far. Using this, you could then calculate the probability that a light cone 80 light-years in extent, centered on Earth, will have already encountered a habitable planet, given the expected density of habitable planets in our galactic neighbourhood. And you could go on further and do a kind of reverse Drake equation and make a guess at how long we've got before those signals encounter an advanced civ. that maybe listening, and then how long to get response from such a civ. .... or when they might show up here?

Also, I believe that if our own radio signals were emanating from another star, we would not be able to detect them because they would be too faint. In other words, unless they were right next to us, we wouldn't be able to detect a civilization identical to our own.

Ah, so you mean this civilisation will try to disguise its signals as some naturally occurring radiation which, when deciphered with the right key, turns into intelligible messages.  Like truecrypt's hidden filesystem block header - looks like random data, smells like random data, but when you poke it just...like...that...... poof! out comes sense.  Those on the receiving end need only know when & where to look.

Could be, I suppose, though you're assuming some civilisation has reason to hide its messages.  In our case, "we've seen no aliens, therefore why should we hide".  Therefore, anyone hiding themselves would presumably be aware of other aliens.  So... either there are no alien civilisations, in which case there are no messages, or there are (at least) two, in which case they are hiding their messages from each other... and from us.

Well, we don't know of any other civ.s out there but we already encrypt signals just to/from each other ;) ... following that tendency along it's current tech. development trajectory leads to more and better encryption, for whatever reasons (mostly because it is a technically superior solution to communicate end-to-end, and thus a default for an advanced civ., and only use broadcast comms. as a poor second best).

This is kind of the point in my OP, that encrypted/masked communications is the default as the technically superior form of communication (using simply the current development trajectory of human RF comms.) and unmasked, broadcast signals will be exceedingly rarely used by technically advanced civ.s, as it would be like expecting modern humans to regularly use stone age tools.

Obviously though, none of this says anything about the expected rate of occurrence of technically advanced civilisations.

You guys should check out this document: http://vault.fbi.gov/UFO/UFO%20Part%201%20of%2016/view

I found page 22 to be particularly interesting, specifically this entry:

lol Mulder what is this?

Yeah, apparently the US Army's a bunch of cock-blockers when it comes to recovered "weather balloons" :)  BTW the info listed on page 22 was obtained through remote viewing, so take it for what you will.

But the fact that this stuff appears on an official government website, plus the fact that FEMA has a chapter dedicated to operating procedures in the event of an extraterrestrial encounter (in their emergency response handbook IIRC), leads one to conclude that the govt does indeed have knowledge of little green men.