In the page about game loop you talk about interpolation, and you say a problem there is is that because it is a guess of the position of the objects, it might be a bit off, we don't really know where the object is gonna be. Maybe it'll be stopped by a wall or something
The error here is that this would be extrapolation rather than interpolation. If instead of interpolating/extrapolating between the last physics update and the next one, we interpolated between the second last update and the last update (both of which have been done and completed - so we don't need to guess anything) objects will never go through walls, or anything like that. There'd be no need to guess :D
From a reader: