Could someone with the knowledge help me to figure out to answer a local woo woo about this????

He has a belief that somehow, the passage of light thru transparent materials, proves Relativity is wrong....He thinks that the light slows down, and this is proof...of something. I told him that light goes thru and if not absorbed, continues to travel at lilght speed. He also believes in something called "slow glass" that was invented/discovered in the middle ages in Europe, and is now some kind of forbidden technology. Supposedly the glass would transmit the image with a delay of time....useful for spying on subjects etc....

I have heard of supposed photographs made in the 17th century, but never seen any proof, maybe he is confused about the supposed nature of this glass. According to the conspiratorial crowd, the Masons have a photo of Shakespeare (Shieks Pir-according to one of them...) that was made with a pin hole camera and a plate of silver in the Bard's time....Has any one here heard about this particular woo woo idea???

Dale in Alabama

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The term slow glass comes from a science fiction book called The light of other days.

Light is slowed within transparent material by slowing the absorbtion/reemission time of individual encounters with atoms. This is the refractive index. Light in a vacuum (between atoms) always travels at c.

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If you really want to blow his mind, you can look up various articles where people have used exotics (Bose-Einstein Condensates, if I'm not mistaken) to slow down and even virtually stop light. They have also managed, by using light pulses, to 'store' the light information and then release it at a desired later time by using a secondary excitation source. Finally, for relatively simple signals, they have managed to propel some of the signals faster than light (not through a vacuum).

But GORT has the right general idea - light does slow down in a material with a different (higher) index of refraction as the initial propelling medium. What this has to do with photographing Shakespeare is perhaps much ado about nothing.

i saw a show on the History Channel about how some people think that the Shroud of Turin is actually a photograph made by Leonardo DaVinci by using simple technology that was available in his time- the reason the head seems to be too "large" for the body is because it was likely photographed separately onto the same cloth that the body was photographed onto.

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Yeesh, like that one hasn't been busted again and again.

The only place I've ever heard the term "slow glass" is here:
http://www.marvunapp.com/Appendix/tymesandson.htm
--describing a comic book story.

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vm,
He's right - and this is the basis of optics and refraction.
See: http://www.bbc.co.uk/scotland/educat...ion2_rev.shtml
But you are right too, in that light continues at its original speed when it leaves the translucent substance.

AS for 'slow glass', this is an imaginary concept, used and re-used in fiction and fable, like many others because they reflect powerful human wishes and desires. EG poisons that simulate death (Romeo & Juliet, Rip Van Winkle), the hidden heir revealed (Moses, Aragorn), identical twins (Comedy of Errors, Count of Monte Christo). Rather better known SF authors have used 'slow glass' such as Robert Shaw and Arthur C.Clarke. The very words "slow glass" have a pleasing assonance that have lead to them being used by artists in photography and film, and it is the name of a fishing fly! Try Googling for them!

John

An individual photon never travels slower than the speed of light in a vacuum. What is happening in a medium is, the photons are being absorbed and then reemitted. This process takes time, so what we percieve as a beam of light slows down, but the actual light itself in its short jumps never travels slower than the speed of light in a vacuum.

This is what G.O.R.T. said, I just thought it might be helpful to expand on it a little.

Thanks for the replies, I think I can explain to him now....and now I remember the SciFi story about the glass and the shroud photo show....

Dale

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