system
Given the following post, respond as if you're commenting on Reddit:
human
[Portal/HL2] Where does the gravity gun come from?

So, the resistence have the gravity gun. But the portal gun also have this technoligy, except a weaker version. Who invented it, was it apature or black mesa? If apature, how did the resistence ge their hands on the technology? Did Black mesa, how did apature sceince get their hands on it? Did they both develop it, or did one and the other stole/copied the tech?
gpt
Both Aperture and Black Mesa (or the ex-Black Mesa scientists) were looking into teleportation technology. It appears likely that gravity field manipulation is either a key part of any teleportation technology or you necessarily learn something about gravity manipulation when you learn about space folding.