While magnets and their field are often pictured like this http://helios.gsfc.nasa.gov/barmag.jpg in reality the field is everywhere like this https://upload.wikimedia.org/wikipedia/commons/5/57/Magnet08... so what the "wormhole" does is, it shields the field from the bar magnet inside the sphere, so only the field from the ends of the bar is projected outside, like this https://d1o50x50snmhul.cloudfront.net/wp-content/uploads/201...