(a physical double travels in the physical world)
First there is the kind of explanation which suggests that we each have a second physical body which can separate from the usual one. There are two aspects to consider, one being the status and nature of the double which travels and the other being the status and nature of the world in which it travels. In this theory both are material and interact with the normal physical world. You may immediately dismiss this notion, saying that the double is non-physical.
To make this theory even worth considering it is necessary to assume that this double is composed of some ‘finer’ or more subtle material that is invisible to the untrained eye. This kind of idea is sometimes expressed in occult writings. The idea appears, for example, as the ‘etheric body’ of the Theosophists. Objections to this type of theory are numerous, and are made on both logical and empirical grounds. First, what could the double be made of? The possibilities seem to range between a complete solid duplicate and a kind of misty and insubstantial version. Another problem with this kind of double is its appearance. If all have a second body why does it appear to some as a blob or globe, to other as a flare, or light, and to yet others as a duplicate of the physical body? Muldoon and Carrington wrestled with this problem and so has Tart .
If the notion of a physical double is problematic, the notion that it travels in the physical world is just as much so. First there are the types of errors made in OB perception. These tend not to be the sort of errors which might arise from a poor perceptual system, but seem often to be fabricated error, or additions, as well as omissions. Then sometimes the OB world is responsive to thought, just as in a dream the scenery can change if the person imagines it changing; and lastly, there is the fact that many OBEs merge into other kinds of experience. The OBEer may find himself seeing places such as never were on earth, or he may meet strange monsters, religious figures or caricature animals. All these features of the OBE make it harder to see the OB world as the physical world at all, and lead one to the conclusion that the OB world is more like a world of thoughts.