"<a href=""https://www.youtube.com/watch?v=zJt8yzR2aoY&amp;t=3m05s"">3:05</a> You can't do that", Game Theory's video on Portal proves it. If you make an infinite loop, one portal gets more mass but it's volume doesn't increase: the other one loses mass but it's volume doesn't decrease. That imbalance will make a black hole. I think we all know what happens next. If you don't know, look up those Kursgesast videos on black holes.