Why haven’t we found extraterrestrials?

 Why have aliens remained silent? The lack of response has a purpose.

The 60-year effort to find alien intelligence has proven fruitless. That's only a moment given the obstacles to interplanetary communication.

Frank Drake, an astronomer, started a test in 1960. He used a radio telescope to observe two neighboring sun-like stars in an effort to look for signals that could only have been produced by planets circling these stars that supported life. 

His mind was blank. Astronomers have continued to listen, attentively and methodically, for the past 60 years since Drake began the search for extraterrestrial intelligence (SETI). However, we have received no word.

One option is that there aren't any aliens at all and that we're the only species on the planet. But considering the expanse of the cosmos and the hundreds of billions of galaxies and stars it contains, most of which have at least one planet circling them, this seems implausible, at least based on our expanding understanding of exoplanetary systems in our own galactic neighborhood.

We haven't yet paid close enough attention or listened intently enough, according to Jill Tarter, co-founder of the SETI Institute in California, to draw any such broad generalizations. In search of signals, astronomers have explored various forms of electromagnetic radiation, including light, radio waves, and gamma rays. 

Such a search must encompass all spatial directions and radii as well as the many ways a signal could appear, such as changes in polarization, frequency, modulation, and strength.

These factors are seen by Tarter as a multidimensional ocean. "We had only examined one bottle of water from that ocean when SETI turned 50. When it reached 60, it resembled a little hot tub more, she said. It is always improving and advancing, yet there is still plenty to discover.