An Out of Body Experience is defined by your awareness being transferred beyond your physical body. I've experienced it myself while practicing Lucid Dreaming Techniques and the process has even been replicated under laboratory conditions.
So, is this proof of the spirit? The afterlife? Alternate dimensions?
Alas, not quite. To trigger an OBE yourself, focus inwards and cut yourself off from your perception of the outside world (what you can see, hear, taste, smell and touch).
Very quickly, your mind begins to create new stimulus of its own. We call these dreams. (This is the crux of the WILD technique for having lucid dreams.)
Usually dreams are reserved for sleep, but as lucid dreamers and OBErs know, it is possible to trick the body into sleep while remaining conscious of these hallucinations. So - are lucid dreams and OBEs the same thing?
To many dream explorers, the answer is a resounding yes. To others, they are completely different phenomena. But the real question is: are OBEs real in the sense that your mind - your awareness - literally leaves your body?
Out of body explorers have long tried to prove this by trying to obtain data from different locations while in the out of body state. Unfortunately nothing truly definitive has been recorded under verifiable conditions. And there are plenty of stories involving OBErs who "saw" their friend sitting at the computer in their OBE, and, lo, when they called them up in real life that's exactly what they were doing.
But science does not accept coincidence or best guesses as proof. That really would get us nowhere in the grand scheme of things.
Perhaps Out of Body Experiences remain one of the true unexplained mysteries of this world. But I feel that with further sleep research we will soon uncover the true mechanism of OBEs and how they differ (if at all) from lucid dreams.