Doctor Who: The Day Of The Doctor's 10 Biggest Questions Answered
4. How Did The Doctors Actually Save Gallifrey?
They used the painting technology that the Zygons had stolen, and transported the whole planet into a single painting. Only on a huge scale, twelve times over. Of course, it wasn't properly explained, because who needs the "quasi-scientific" stuff when we're about to see all the Doctors return? Or maybe they did explain and I didn't listen in all the excitement.