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However , in order to give the series as authentic a veneer as possible , Geoffrey Hoyle , son of physicist Fred Hoyle and a noted science fiction author in his own right , gave his advice regarding how time travel might be possible .
 Geoffrey Hoyle, Fred Hoyle
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 Geoffrey Hoyle, Fred Hoyle