Why is SETI searching for unusual signal patterns, and not higher levels of randomness than found in background radiation?

Question

Maybe this is a (very) stupid question, but anyways, I was wondering about that lately just for fun.

So SETI is basically searching (among all the noise coming to use from space) unusual (repeatable) patterns among all the noise from outer-space we capture on Earth.

But what if this is the wrong way to look for possible alien-signals? What if alien (or us, the same thing) know, that another planet (from huge distances) will receive mostly noise (I know, this already contradicts the stuff below, but anyways) and nothing else (so maybe quite impossible to detect any useful signal-pattern).

So, if we consider received noise as highly random, what if aliens transmit on purpose there signal encoded in super-random-way? What I mean to say is what if SETI should look about quite abnormal-randomness (e.g. super random noise) on received signals?

Of course, decoding this super random noise is another question :).

Answer 1

Then we have no way of distinguishing that from natural random noise.

Even highly compressed data contains patterns, although their complexity is so high, that distinguishing them from natural noise without knowing the algorithm is nearly impossible. A good cryptogram is indistinguishable from random noise without knowing the complete key on top of the algorithm. Good spy techniques hide even the signal level below the background noise level (and provide a lot of error correction to allow extraction of that signal) so that even looking for sources of random noise won't locate the source of the signal.

If your intent is to be detected, you will create signal as distinct from natural "noise" as possible, a clear order. And it doesn't matter how advanced technology you have at your disposal, you still use primitive, clear means to convey your message. A rescue ship, despite complex radars and advanced radio, will have a mast with powerful light source, to be visible from a long distance by the stranded, so they could signal their presence, e.g. using a flare or lighting a fire. A fighter plane intercepting an unidentified (civilian) airplane illegally entering the airspace, despite all the complex electronics, besides hailing on unencrypted channel of general hailing frequency, will shine a spotlight at the cockpit of the plane, making itself obviously visible.

Because recognizing and distinguishing simple, clear and obvious signals is way easier - and way more likely, than spotting discrepancies in white noise. SETI too doesn't really hope to encounter a signal addressed to us. It seeks signals exchanged between the aliens, trying to recognize and distinguish them. And since these will most likely be compressed (bandwidth savings!) they hope for spotting patterns.