The idea that the soul can somehow be quantified or recorded at the time of death goes back over a century. The most famous scientific experiment on that topic was conducted by Dr. Duncan MacDougall, who in 1907 tried to measure the weight of the soul. He weighed a half-dozen terminally ill patients before, during, and after death, concluding that there was an average of 21 grams difference in the weight of the bodies before and after death. His experiments were badly designed, however, with a tiny sample size and crude measurement tools. More modern measurements find no such effect, though the myth that the human soul weighs 21 grams remains today.
So if the vertical whitish thing in the photo isn't a ghost, what is it?
Vazquez has denied that the image has been altered, and there's no reason to think it has. It's much more likely to be an ordinary object that has taken on a spooky context because of the circumstances; in other words that same photo could likely have been taken at that same spot a day earlier, and no one would have associated it with anything odd or tragic.
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Writer Hemant Mehta offered the following explanation on his blog: "It could easily be a discolored tree trunk. Seriously. I pulled up a Google Maps image of Highway 15 near Stanton, Kentucky where the accident took place. I don't know if this is the exact spot, but it was *very* easy to find a discolored tree trunk in the image."
It's difficult to tell what exactly the image is, but the image shows other foliage emerging from the shade of the trees in the same area; a tree trunk or light-colored branch is a real possibility. It could also be smoke from the wreck, though the motorcycle seems to be off to one side.
In any event, it's noteworthy that apparently no one at the scene reported seeing anything unusual, nor the supposed apparition just above them.
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There's also the question of what color the soul, spirit, or ghost is-or would be. Ghosts are often assumed to be invisible, though they are also claimed to appear in a wide variety of forms including white round spots in photos (known as orbs in ghost hunting lingo); vague, shadow-like mists; whitish blobs; and even appearing completely like an ordinary person.
In fact the public's idea of what a soul or spirit looks like has changed over time; in his book "The Haunted: A Social History of Ghosts" researcher Owen Davies of the University of Hertsfordshire notes the "long tradition of Christian pictorial representations of souls ascending to heaven in the form of naked children. They, along with doves, symbolized the innocence and purity of the soul once freed from the polluted body." The idea that a vaguely human-shaped misty white form would be a soul is a fairly modern idea.
Because people love a mystery, not to mention sharing weird photos on social media, especially when the theme involves the afterlife, angels, and the dead, it's not surprising that this ghost photo went viral.