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Invisible matter?

plindboe

Graduate Poster
plindboe
Joined
Apr 4, 2003
Messages
1,246
I once saw a science program, where the host placed a small glas jar inside a larger glass jar, and filled a particular kind of liquid in both jars. I have forgotten what this liquid was unfortunately. The funny thing is, that when looking through the big jar, the smaller jar had become entirely invisible. The reason he gave was that the bending angle(Not sure if this is the correct words in English) was the same for the liquid and the glas.

Now, could it be possible, in a near future, some material is discovered where the light will pass through without bending so it could be virtually invisible?
 
They matched the refractive index of the glass and the liquid. We do the same thing to make clear consumer products. Regarding the next part, are you thinking of something that will make an opaque object (like a body) invisible? Not possible in this way, although they are developing lcd fabrics that can project the image behind it to appear "invisible".
 
Refractive index matching.

If the refractive index (ratio of speed of light in vacuum to speed of light in medium) is the same in both media there is no optical interface, and therefore no scattering. By 'bending' he means 'refraction'. Look up 'Snell's law' for more information.
 
I'm simply talking about a single material that will be invisible in air. I guess, the reason we can see glas, is because of the different bending angles of air and glas. I'm thinking, if one then invented some kind of material where light can pass through, like glas, but instead where the light isn't bent, then it would be invisible.
 
plindboe,
I think you are asking if it would be possible to develop a solid material that had the same refractive index as air which would thereby render that solid material essentially perfectly transparent.

I have always assumed that this was impossible, because it seemed unlikely that one could devolop a solid material that light would travel thru at roughly the same velocity as light travels thru a vacuum.

I wonder if one understood quantum maechanics and/or light transmission thru solids better than I do (which isn't too well) that one could say definitively that no such material could be developed. I think this is a question for one of our resident geniuses (tez, S. Cat, etc.).

Meanwhile, I would hold off purchasing any shares any companies touting solids with refractive indexes equal to that of air.
 
davefoc, wow nice answer. It certainly sounds sensible that it wouldn't be possible then. But perhaps something which could be invisible in water then instead? The ultimate murder weapon. ;)

But perhaps one day, scientists could learn to manipulate the speed of light through matter through some strange means.
 
Hmm - refractive index of air is pretty close to that of vacuum, so seems unlikely that one could construct a solid object with the same value. Perhaps a series of objects with varying indices can be used to compensate for each other and achieve the same effect? Though to achieve the exact same effect as with the two jars I think the observer would have to be outside of the medium (air) so had better be able to hold their breath! Since every material will have some finite absorption length, it'll never be perfect...

Glass with an antireflective coating is pretty near invisible. Heck, ordinary glass is apparently invisible to me once I've had a beer or two (he says rubbing his head and remembering the time he walked into the glass sliding door at home....)
 
One thing to remember is that /only/ the object would be invisible in air. If you decided to, say, make a suit of cloths out of Invisi-brand fabric (tm), you wouldn't become invisible when you donned it. Rather, you would have a situation not entirely unlike the Emperor's New Cloths.
 
And what's more, how would you ever find an item that was made of this material?
 
Wasn't there some sci-fi story in Analog, or something where a beach house had a window facing the ocean paned witha special kind of glass that slowed the passage of light through it so that one had a super slowmotion view of the ocean?

I think the plot was that a murder was committed in front of the window and they were waiting for the light to "catch up" so they could see the act and catch the killer.

Hmm...
 
davefoc said:
plindboe,
I think you are asking if it would be possible to develop a solid material that had the same refractive index as air which would thereby render that solid material essentially perfectly transparent.

I have always assumed that this was impossible, because it seemed unlikely that one could devolop a solid material that light would travel thru at roughly the same velocity as light travels thru a vacuum.

I wonder if one understood quantum maechanics and/or light transmission thru solids better than I do (which isn't too well) that one could say definitively that no such material could be developed. I think this is a question for one of our resident geniuses (tez, S. Cat, etc.).

Meanwhile, I would hold off purchasing any shares any companies touting solids with refractive indexes equal to that of air.
Click to expand...


Minimizing reflectance is often an important issue in many different optical arrangements. While reflection losses from a single air/glass interface may only amount to a few percent, many such interfaces in succession (e.g. lenses, beam splitters etc.) will quickly attenuate the beam.

Actually, a zero reflected intensity can be achieved (in principle) quite easily. One only needs to coat the material (assumed transparent) with a film of thickness (n/4)*lambda, where n is an odd integer, and lambda is the wavelength. This results in destructive interference between the beams of light reflected from each interface (i.e. from air/film and film/object). If the ratio of refractive indices is chosen correctly, the reflectivity can be made zero (again in principle). Real designs often involve multilayer coatings for better, and also broadband, performance.

So this is a bit of a trick of course but it means a transparent object can be made to seem as if its refractive index is trivial (for normal incidence at least).

Edited to add: Tez has already mentioned antireflection coatings. Sorry.
 
c0rbin said:
Wasn't there some sci-fi story in Analog, or something where a beach house had a window facing the ocean paned witha special kind of glass that slowed the passage of light through it so that one had a super slowmotion view of the ocean?

I think the plot was that a murder was committed in front of the window and they were waiting for the light to "catch up" so they could see the act and catch the killer.

Hmm...
Click to expand...
One of Bob Shaw's "Slow Glass" stories, either "The Light of Other Days" or "Burden of Proof". I never read either, but on the book identification boards where I hang out, people ask about them continually.
 
c0rbin said:
Wasn't there some sci-fi story in Analog, or something where a beach house had a window facing the ocean paned witha special kind of glass that slowed the passage of light through it so that one had a super slowmotion view of the ocean?
Click to expand...
Wouldn't that give a delayed view at normal speed?
 
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