The Search for Extra-Terrestrial Intelligence (SETI) fascinates me, but one thing I've never had anyone explain to me is how we'd be able to distinguish intelligent signals from from the background noise. After all, I assume that advanced alien civilizations have decent encryption and data compression technology, and encrypted data looks like random data if you don't have the key.
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My impression is that we're looking for signals from aliens deliberately announcing themselves, not eg. snooping for ancient and distant credit card numbers.
Even that is a hard enough task. Imagine the related problem of producing a message for aliens to read: what would you say, and how would you encode it?
Here's an attempt: http://www.kimbly.com/blog/000431.html
And it starts off with a 2D image arrangement which you would have to establish over a broadcast signal first...
J.
Even an encoded or compressed message will have an internal structure that will make the message possible. For example, a computer file will consist of ones and zeroes of the same size at regular intervals. You don't have to understand the meaning of the arrangement of ones and zeroes to see that they are coming in some regular sequence. Random noise wouldn't have so much internal structure.
Mauyr: Oh huh, I always figured we were just trying to detect emanations from another technological society. Aliens who were purposefully trying to be detected would certainly have easier-to-recognize data streams.
BB: I'm not sure you're right about that, but I don't know enough about analog or multiplexed encrypted data streams to be sure. Plus we don't know what data rates or frequencies they'd be using. It's possible the Cosmic Background Radiation is really just a giant diffuse alien data network we don't know how to access :)