Ghosts are to light what echoes are to sound. The standard description of a ghost is that it is white, transparent, and often looks like a real being that once lived, although some experience ghosts as if they were real and alive in the here and now. If someone sees a ghost, the place where it is seen is said to be haunted. You already know that.

People who report seeing ghosts are considered suspect, but some historic  people believe that they have seen ghosts. Among them were Biblical figures such as King Saul and Jesus' apostles and, more lately, Abraham Lincoln. Many people have reported seeing Lincoln's ghost in the White House.

If it is true that a ghost is to light as an echo is to sound, from where does the light reflect or bounce to produce the image of a ghost? If you are willing to accept this as a premise, how far into space can light go and still return to earth as an "echo"?

If you are wondering about how this could possibly be true, consider ground penetrating radar, which shoots a beam of light from a height, which beam of light returns to its source so that it gives a picture of all the activity and disruption caused by both man and nature. These are geologic ghosts, images of what was once real and visible.

Both laser and ground penetrating radar equipment can examine the ground and tell what type of usage and travel the land has experienced very far back in history. The equipment that does this translates its findings so that historians and archeologists can tell that, for instance, a wagon train once crossed the land, even though there is no such discernible evidence to be seen by the human eye.

Energy and matter are interchangeable, one being converted into the other constantly. 

If you are tempted to say that ghosts are not real, consider that in the book The Holographic Universe by Michael Talbot that "there is evidence to suggest that our world and everything in it- from snowflakes to maple trees to falling stars and spinning electrons- are also only ghostly images, projections from a level of  reality so beyond our own it is literally beyond both space and time."

Most often, ghost stories and ghosts are associated with a traumatic event such as a murder or some other tragedy. A ghostly scene can also involve sounds such as weeping, screaming, rattling chains, music, and groaning, just to mention a few of the classics. A truly compelling apparition includes echoes of sound and light, both traveling in the form of waves.

Ultrasound is produced by a sound wave that is interpreted as a picture when the ultrasound device measures the difference in tissue density. The difference shows up as light and dark areas as well as an outline of the object being examined. The reflected "sound" is interpreted through a device that produces a picture based on the varying levels of tissue density. When an ultrasound technician bounces the sound off the tissues of an unborn baby in utero, the picture produced is white and, you might say, ghostly. Since most people are familiar with and understand what is being seen, there is little fear associated with ultrasound procedures.

Originally, yodeling was developed as a form of communication. It enabled yodelers to communicate across large distances. Yodeling is a good example of using echoes for a practical purpose. Musically speaking, yodeling depends not only on echoes, but echoes that can produce a multi-pitched musical composition. The yell from a yodeler bounces off a nearby mountain, as in the case of Swiss yodelers. However, this blog is not about the musical aspect of alternating chest voice with head voice; it is about the physical elements of echoes of sound and light. Yodeling is a small model of time travel. The departing trip and the return of the sound, ida y vuelta, is miniscule compared to the distance light would have to travel to be bounced back as a ghostly image.

Could the moon be reflecting ghostly light? The moon's surface reflects the sun's light so brilliantly that it seems that the moon is actually generating the light.

Ghosts are not forever. There are books about ghostly legends, that tell the story about ghosts that once were seen, but are no longer seen. Has their light faded as echoes gradually fade to silence?

Consider that even in these days ghosts are reported manifesting themselves. The light of these ghosts is strongly visible.

Where there is sound, there is an echo, but usually the reflected sound, once made, has to travel such a short distance that the echo-sound happens almost simultaneously with the original sound, so the echo is not heard.

An echo does not return at the same intensity as the original sound. The echo sound is modified by reflection, refraction, diffraction and transmission, and is diminished and/or changed during its return.

A hologram is a scientifically produced ghost. Holograms rely on lasers. L.A.S.E.R. stands for Light Amplification by Stimulated Emission of Radiation. A laser light is a beam of light in one color that does not spread out like sunlight. The beam is focused by the use of mirrors and lenses. Laser light can be used to produce what appears to be a 3D or floating image. If you remember what Princess Leia's "holographic" image looked like in Star Wars, you'll see that her image could be said to resemble a ghost. Some images that appear to be holograms, such as in Disney's Haunted Mansion, are illusions, but they do rely on the careful manipulation of light. In the case of these illusions, "By varying the lighting, it is possible to show each manikin separately, or to superimpose both of them. A disadvantage of this is that only a few visitors at a time can see the illusion".
(http://www.pangolin.com/resguide03b.htm)

The appearance of ghosts, similarly, is rarely seen by more than one or a few people who are usually grouped in basically the same spot and looking at the spectral image from the same direction. That pretty much describes an audience viewing a hologram.

An echo loses strength each time it makes the trip from the "yodeler" to the mountain and back. Perhaps that's why many "ghosts" gradually stop making appearances. Ghosts seen a thousand years ago may fade, but new ghosts closer to our present time are also described. Perhaps the light of various apparitions bounces back from myriad and sundry places. Wouldn't we like to know the truth about this?