It’s a big galaxy out there. Even the most skeptical scientist has to accept that if a civilisation like our own exists, then there’s a good chance we’re not the only one to have ever done so. When most people think about SETI (the search for extraterrestrial intellgence), they imagine someone like Ellie Arroway searching the skies for radio transmissions. But what about looking in other ways? Perhaps a highly advanced alien civilisation might build structures large enough for us to see.
Vast structures, constructed on astronomical scales by advanced civilisations, is what the field of astroengineering is all about. This, admittedly, sounds audacious – and for the human race right now, it is. For us, astroengineering is still very much the realm of thought experiments, theoretical calculations, and science fiction. So it may be surprising to know that certain astronomers have made some quite serious attempts to look for astroengineered artifacts around other stars. With telescopes becoming ever more sensitive, and images being taken of exoplanets, the idea is starting to captivate imaginations once more.
For the rest of the story: http://www.universetoday.com/102348/hunting-for-alien-megastructures/