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By considering the propagation of the negative energy modes of the electron field backward in time , Ernst Stueckelberg reached a pictorial understanding of the fact that the particle and antiparticle have equal mass " m " and spin " J " but opposite charges " q " .
 person: Ernst Stueckelberg
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
 Entities: Ernst Stueckelberg 
Answer:
 person: Ernst Stueckelberg