Why haven’t we detected a signal from intelligent aliens yet?

[Cypress]

Let's say there was an advanced civilization a mere 10 light years away - but it died out 5 billion years ago. We are dealing with vast distances and vast amounts of time. Even if there were millions of advanced civilizations across the galaxy, the chances of ever making contact are infinitesimally small.

I don't think the idea realistically is to establish contact with a contemporaneous advanced civilization.

The idea is to monitor for signals that may have come from civilizations that existed in the past. There are probably hundreds of millions of star systems just within 5000 light years of Earth. The WOW signal detected at Ohio State University in 1977 has never been adequately explained, but was thought by at least some to be an artificial radio signal source. It came from somewhere in the Sagittarius constellation two thousand light years away. So if it was an artificial signal (highly debatable), it was from a civilization that existed thousands of years ago.

 

[Cypress]

When we do, it will be by chance. We probably haven't even touched more than 1% of the night sky. I also wonder how much red shift we'd have to adjust for in order to get some signal from stars that are moving...

Red shift is not caused by stars moving away from us strictly speaking, it is caused by the space between galaxies and stars expanding. Since we have a pretty good handle on the Hubble Constant expansion of space, I don't see we would be fooled by radio, microwave, or visible EM since we can account for how much they are stretched before reaching Earth

 

[Dutch Uncle]

I can't deal with your whining right now. You intentionally chopped off my statement where I wrote we should keep looking because it's possible alien life is out there.

I'd give up trying to reason with unreasonable people.