The Oxford Dictionary defines an expert as "someone who is practised and or skillful in an area or subject." So we can clearly say that the Big Think "Experts" are not experts in all of the areas that they post in. It is clear, however, that they are "practised and/or skillful in an area or subject." The term expert as it is used in Big Think is not in reference to the area that the person posts in it is that they are a person who is recognised as an expert or smart person.