Ka is an Egyptian spirit from the Ghostbusters RPG's Tobin's Spirit Guide (RPG).
We have the ancient Egyptians to thank for the earliest recorded commentary on a phenomenon of the spirit world that is unequaled by any other, both in the frequency of its occurrence and in the effect it has on the human race.
From what we know of genetics, even though that science is still in its infancy, we have good reason to believe that no two people living on earth, even so-called identical twins, look exactly alike. From there it is a short jump to the theory that each of the thousands of millions of human beings who has ever lived is in some way visually distinguishable from all the others.
Yet, every person does have a double--an absolute duplicate of himself or herself in appearance and mannerisms. This "other person" spends at least some of its existence in the realm of ether. If and when it travels to the physical realm, it can produce a remarkable, perhaps pivotal, change in the life of the mortal being whom it mirrors.
The Egyptians used the word "ka" to refer to the essence of each individual human being--those qualities and properties that set the person apart from all others.
Through the ages, this type of spirit has been given many names by many cultures, and a myriad interpretations have been attached to the significance of its appearance. In Scotland this spirit is called the fetch; in Germany, the doppelganger, and in both of those cultures it generally has a negative connotation--a person who sees his double is soon destined to die. Jewish lore, on the other hand, maintains that to see one's double is good luck because it endows the person with the ability to know his own future.
The truth of the matter seems to be that encountering one's double produces a result that is as unpredictable as the fact of whether or not the double will appear to begin with. The result of a meeting between a person and his other self depends on uncountable variables. All we can do to prepare ourselves for the possibility is to believe that the possibility exists- and that is the only purpose that this essay can hope to achieve.
A double may try to communicate with one either vocally or through gestures. It may remain mute and motionless, leaving its victim to imagine or deduce why it has come. It may appear not before its victim but before people who know him, and it may do or say something that he benefits from or suffers for at a later time.
Do not go looking for your ethereal ka, for whether I or not you find it is not up to you. Do not try to predetermine what will happen when it does appear, because you cannot dictate the circumstances under which that might occur. Just be aware that it could happen, and live your life accordingly.