The logic of this endeavor is as unassailable as its prospects are rickety. Sentient beings anywhere in the galaxy, having reached a certain level of technological sophistication, would realize that the distances between stars are physically unbridgeable and would likely choose to communicate with radio waves.

But joining the cosmic conversation, if there is such a thing, would require us humans on the listening end to know which of 100 billion stars to point our receivers at, and which frequency to tune in to. That’s an optimistic scenario. And, of course, we would have to be able to figure out what they are saying once we heard it.

We now know that there are billions of other planets in the Milky Way galaxy alone. Thanks to efforts like NASA’s TESS satellite, we are beginning to discern some details of the closest ones. We know that they can look at us just as we are looking at them.

These days, one of the most extensive searches is being made by Breakthrough Listen, a program underwritten by the billionaire Yuri Milner and his friends. Seti@home has been piggybacking on its telescopes, looking at whatever they are looking at.

Once upon a time, almost 2 million computers were subscribed to the program, but it has since declined twentyfold. As the seti@home team explained in a recent conference call, they have been able to gauge the average lifetime of personal computers by how long they remain registered on the website — about three years.

All this has not happened without a few ruffled feathers. Legend has it that some I.T. administrators have found their networks bogged down by too many people running the screen saver at once. Dan Werthimer, who holds the Watson and Marilyn Alberts SETI Chair at the University of California, Berkeley, said this was overblown. Once, he said, a school administrator got in trouble after downloading seti@home to all the computers in the school. But after 21 years, the team doesn’t yet know whether their screen saver recorded any alien signals.