Answer:
The propagation of electromagnetic waves either in a certain medium or in vacuum is due the the mutual changes between the electric and magnetic field. Referring to the four maxwell's equation and from the wave equations of the electric and magnetic fields, any one can conclude that the spatial variation of of the electric field is always accompanied with a time varying of the magnetic field and hat the spatial variation of of the magnetic field is always accompanied with a time varying of the electric field. These variations in electric and magnetic fields fields lead to the transfer of the energy which is carried by the EM wave. Therefore, EM waves will constantly propagate with non stopping until meet an obstacle or barrier.
