Naked Science Forum
General Science => General Science => Topic started by: virginia_sue on 28/10/2003 17:02:34
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I know sound can bounce around endlessly and echo back under the right conditions so that it's possible for an old radio broadcast to be heard many years after the broadcast is no longer being sent out. My questions is - is it possible that the image of a person could be left behind somehow or way much like a radio wave and that under the right conditions it could actually be seen as a faded or transparent image giving you the impression of seeing or being visited by someone who has died. I do understand there is a big difference in a sound wave and a image of something or someone, is it at all possible for an image to linger and be seen again, could light waves become trapped and reflect back a persons image creating what people would mistake for a ghostly apparition? if this is not in anyway possible can someone explain to me the reasons why it's not possible. Thank You.
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The reason echos become fainter is because the walls or surface that bounces the sound absorbs some of the energy. There is no such thing (at least I don't think so? correct me if I'm wrong) as a surface that can reflect sound or anything else perfectly, the image or whatever would dissappear in a short time, therefore I do not think it is possible.
Am I dead? Am I alive? I'm both!
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Welcome virginia_sue, that's a really interesting concept. I believe that is possible, though some may think of it more as time travel.
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The speed of light is so fast and there fore the loss of it would be, as well. Think of a movie projector. If you put your hand in front of it while projecting an image, you see your shadow, as opposed to a lingering image. Also, you would not see the image reflected from your hand on any opposite walls. So, my guess is that light disipates so fast that it wouldn't linger. The waves are too tight and fast. That's just my layman's guess.
Welcome to the forum.
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Quantum, in rare instances there is a perfect reflector, a superconducting mirror. In practice, there is no such thing that lasts more than a very short time under highly controlled circumstances. Otherwise, even the very best (laboratory grade) mirrors will dissipate light to well below human detectability in a small fraction of a second.
Being a radio engineer, I've never heard of radio signals bouncing around and being received years later. If the signal was going away from earth and bouncing back, even bouncing off Pluto at its farthest from Earth, the signal would be back in a little less than 14 hours. In this case, the signal would be so weak that only the very best antennas and receivers would have any hope of detecting it.
Welcome to the forum Virginia Sue! I would like to find out more about the old transmissions you asked about.
John
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deleted as inapproprate
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I know sound can bounce around endlessly and echo back under the right conditions so that it's possible for an old radio broadcast to be heard many years after the broadcast is no longer being sent out. My questions is - is it possible that the image of a person could be left behind somehow or way much like a radio wave and that under the right conditions it could actually be seen as a faded or transparent image giving you the impression of seeing or being visited by someone who has died. I do understand there is a big difference in a sound wave and a image of something or someone, is it at all possible for an image to linger and be seen again, could light waves become trapped and reflect back a persons image creating what people would mistake for a ghostly apparition? if this is not in anyway possible can someone explain to me the reasons why it's not possible. Thank You.
I don't think such thing is possible as a natural phenomenon (but, who knows?), however it's certainly possible as an artificial one, because it's already been done in laboratories. It's called "frozen light". A BEC condensate (a very cold atomic cloud in a peculiar quantum state) can slow down a light pulse, so slowly that it can remain trapped in the cloud even for a long time. In this way reaserchers try to store an entire image in such a tiny cloud, as a possible application for future computer's memories and CPUs. See, for example:
http://www.physics.hku.hk/~tboyce/sf/topics/lightfreeze/lightfreeze.html
Fascinating, isnt'it?