Originally Posted by **********

The odds of us being spotted by someone else in our galaxy are fairly high, because the earth is the "brightest" radio source. If someone somewhere pointed a radio telescope in our direction, and they were less than about 120 light years away, we would blind them with non-natural radio waves.

The same would be true if we were looking for them.Even if there were advanced cilivilsations out there, we just could not see them unless they had been producing radio waves, or artificial light, or other forms of electromagnetic energy for a very long time. The greater the distance, the longer they must have been doing this.