"<a href=""https://www.youtube.com/watch?v=zJt8yzR2aoY&amp;t=3m10s"">3:10</a> If this is actually a portal you have to think about the physics more carefully than that.<br>From the perspective of the top portal", there's an entire planet trying to attract you inside of it. <br><br>Potential energy between portal boundaries should be continuous, otherwise trying to pass through one will rip you apart since force is the derivative of the potential energy.<br>The thing is, if potential energy between portal boundaries is a continuous function then you can't extract energy out of it. You'd just kind of hover in mid air around the equilibrium point.