[Tigbit]

Yes they can be an extension of the familiar 4 dimensions. But the concept of higher planes of existence in metaphysics can simply be higher dimensions. The two concepts can be interchangeable for all intents and purposes. The commonly refered to deity called God could reside in the higher dimensions as well as the lower... just as we reside in the 2nd and 3rd spacial dimensions at the same time as the first. Just as all three spacials are a part of our experience of the universe, our three and the higher dimensions are a part of the deity construct of myth.