While alien activity has never been detected - and it should be pretty easy to see at this distance -the "hollow moon" theory does provide a fairly satisfying reason as to why. But is the theory itself probable? Let's take a look. First up is the evidence provided by Russian researchers in the 1970 Sputnik journal, who analyzed metal composition, crater sizes, and relationship to the Earth in an in-depth study.
What they found surprised even them. Although unwilling to admit it, even they were forced to agree that the moon was, in all likelihood, entirely hollow. There was basically no other way the data could line up in that way. Though they've since denounced their own research, many agree that this was purely due to the pressure put on their professional careers, rather than actually thinking they were wrong.