We all know Portal and Half-life exist in the same universe, but what about TF2? We assume TF2 is based around the 1950/1960's which is the same for Old-Aperture. Recently the Blu and Red teams have had to fight for control of Australium as well as the gravel pits but what if Australium is an additive to moon rocks to create portal gel and the Mann brothers knew this and struck a deal with Cave Johnson to supply him with it and Cave brought in Saxton as a third-party weapons supplier giving the teams the latest scientific weaponry and the Engineer prototype turrets and teleporter frames, something we don't hear of again until Portal testing begins. Because Glad0s and the Administrator are voiced by the same woman it's possible that Caroline was in charge of these experiments and would explain her lack of remorse when testing other subjects and killing her creators as her hatred carried over into her next life. Grey Mann was introduced to us last year as the murderer of the Mann brothers and creator of the Machines, the administrator's reaction to this shows us that he is an enemy of Aperture but the fact he has made functional robots, although clunky, shows that Aperture may have taken his creations and used them to piece together New-Aperture and Glad0s. Post your thoughts on my theory below and don't forget to leave a thumb.