Do we know for sure if schizophrenic voices come from inside people's heads or could it be communication from semi-parallel dimensions like how scientists say dinosaurs are walking in your living room?
When a schizophrenic person hears voices without an actual physical presence of any sort of voice or sound from any source, it is called as Auditory Hallucinations. These happens because of the schizophrenia,the disorder the person is going through not due to any kind of semi-parallel dimensions. These voices which the person hears are due to activation of certain parts of the brain which end up in these hallucinations which can even make the patient suicide or hurt himself/herself and his/her surroundings.
Schizophrenia is a complex mental disorder and includes many other symptoms,the patient also experiences other forms of hallucinations and delusions.