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In a few comic books the Doctor has, in his fourth and eleventh incarnations landed on the Enterprise. Regardless of whether Kirk or Picard he has entered the trek universe but in "The Impossible Astronaut" an elderly woman asks a member of The Silence if his costume is from the Star Trek show.
My question is, can the Star Trek universe and 'Whoniverse' coincide with each other? Also if they can be linked together could the aliens from Star Trek appear on Doctor Who? I feel as though mixing them would give a larger audience to both shows. Would there be as many legal complications in using the aliens like romulins, volcan, borgs etc... in Doctor who?