In 1982 or so, Eric Drexler had the idea of looking at photographs of the nearer galaxies and seeing if any had circular areas of darkness in them, suggesting a spreading civilization. It was in an atlas of galaxies, that had one galaxy per page, so a few hundred galaxies at most. At least that’s what I remember from talking to him about it at the time.
Since then, automated galaxy surveys have looked at millions of galaxies, with “funny looking” ones reviewed by humans. That’s how Julianne Dalcanton found Comet Dalcanton, for example: the program kicked it out and said “What’s with this funny looking galaxy?” And when she looked at it, she realized it was not a galaxy, but a comet. Perhaps this kind of survey would turn up a civilized galaxy, but I don’t know how to estimate the probability of it being detected.
In 1982 or so, Eric Drexler had the idea of looking at photographs of the nearer galaxies and seeing if any had circular areas of darkness in them, suggesting a spreading civilization. It was in an atlas of galaxies, that had one galaxy per page, so a few hundred galaxies at most. At least that’s what I remember from talking to him about it at the time.
Since then, automated galaxy surveys have looked at millions of galaxies, with “funny looking” ones reviewed by humans. That’s how Julianne Dalcanton found Comet Dalcanton, for example: the program kicked it out and said “What’s with this funny looking galaxy?” And when she looked at it, she realized it was not a galaxy, but a comet. Perhaps this kind of survey would turn up a civilized galaxy, but I don’t know how to estimate the probability of it being detected.
Here‘s a 2015 study that looked for Dyson spheres in 1359 galaxies: https://iopscience.iop.org/article/10.1088/0004-637X/810/1/23