1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution We are often told one reason why an electron does not fall to the centre of atoms is because it would then have a well-defined position. Any two particle which comes into contact define each others positions and so their momentum becomes very large. How then is it, according to the Exclusion principle two bosons can actually occupy the same space? Surely that would violate the UP?