Sentence:  “They have numerically confirmed, perhaps for the first time, something we were fairly sure had to be true, but was still a conjecture — namely that the thermodynamics of certain black holes can be reproduced from a lower-dimensional universe,” says Leonard Susskind, a theoretical physicist at Stanford University in California who was among the first <WSD>theoreticians</WSD> to explore the idea of holographic universes. 
Meaning of the word marked with <WSD> tags:  a theorist