>>718464309
To illustrate that final point, let's finally turn to hula hoops. If we now add another friendly astronaut to the blue side (surprise, it was in space all along) who, once again, moves with the cube, what does he observe? A stationary cube emerging from a portal that's moving away from him (you could add some rocket boosters to the back of the portal to cause a sudden stop once the cube is through, much like a falling hula hoop is suddenly stopped by the Earth - but, of course, this once again wouldn't affect anything, just as the orange portal stopping once the cube is through would not affect anything). So yes, you can create a hula hoop effect with a portal, using the same principle of symmetrical relative motion. It just requires that you do something else than the actual setup of the Portal problem.

>>16739071
To illustrate that final point, let's finally turn to hula hoops. If we now add another friendly astronaut to the blue side (surprise, it was in space all along) who, once again, moves with the cube, what does he observe? A stationary cube emerging from a portal that's moving away from him (you could add some rocket boosters to the back of the portal to cause a sudden stop once the cube is through, much like a falling hula hoop is suddenly stopped by the Earth - but, of course, this once again wouldn't affect anything, just as the orange portal stopping once the cube is through would not affect anything). So yes, you can create a hula hoop effect with a portal, using the same principle of symmetrical relative motion. It just requires that you do something else than the actual setup of the Portal problem.