What kind of scientific breakthroughs would be necessary to render living or nonliving things optically invisible? (Not merely just well camouflaged.) (I’m not talking about things like the Philadelphia Experiment or other similar myths.) What kind of power (and how much of it) would be needed?
Has this ever been (or is it currently) under serious scientific study?
Shanasty’s second link talks about reducing reflections from a body, but of course even if that was 100% successful it would just leave a fairly prominent black shape in the room. In any case at visible light wavelengths it can only work with tiny objects.
The technology in the first link only works at one specific angle of viewing, and relies on a projected image being indistinguishable from the real thing.
It would not be possible to make light travel through otherwise opaque objects. The closest you could come is somehow making the light bend around an object and re-assemble itself on its way to you, but as objects in the real world are routinely illuminated from all angles this is not really achievable either.
If this were achievable, the invisible person would be blind, right? Because no light would reach their eyes.
I’ve had a science fiction idea in my head for about a decade now.
A ship (it’s science fiction/fantasy, so it’s a space ship) or a uniform would be covered with very, very tiny camera/screen units. These units would simultaneously capture the images in front of them, and display an image as well. The units on one side would capture images from that side and simultaneously display the images captured by the units on the opposite side. Since the display is of what is behind the ship or person wearing the uniform, the ship/person would be invisible. Same thing if a viewer was on the other side. Or any side, since the entire ship or person would be covered.
A television has pixels that combine into an image at a very short distance from the screen. So the camouflage would be effective even at close range if the camera/display units were pixel-size or smaller.
A decade ago when I thought of it, it was sheer fantasy. With today’s nanotechnology? Maybe not so much.
The military is heavily investing in the type of camouflage depicted in Shagnasty’s first link. In fact, if you have The Military Channel on your cable TV lineup, I’m sure they run something on this every few weeks.
Remember: the idea - well, the military idea - isn’t to make someone “invisible” so much as to make them difficult to shoot. Standard camouflage was designed to break up the human silhouette against a wooded backdrop, not to make them undetectable. The same theory is at work here, only an invention such as the first link allows for changing backgrounds\scenery, which is pretty cool if you ask me. A soldier could go from city to forest to desert without having to change his uniform three times to match the scenery at each location.
For another interesting take on camouflage, check out “dazzle painting”, a WWI techonolgy where ships were painted in various outrageous colour patterns - again, not to make them invisible, but break up the ship’s outline and so make it difficult for German U-boats to figure out a ship’s exact speed and direction.
Hm. Read Shagnasty’s links. The first one looks similar to what I had in mind, only mine is self-contained. I wonder if it’s too late to get a patent?
it would only take one new twist on fairly old tech, you have noise cancelling headphones, the way these work is by picking up incoming noise and playing the exact opposite wave length creating silence when the 2 combine.
just find a way to intercept light from all diections and transmit the opposite wavelength in all directions and your problem is solved.
This wouldn’t work becuase what is on the other side of a point depends on the angle you are looking at it.
Red… .Blue
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Obs 1… Obs 2
If you imagine the intersection of the lines to be where the object is you can see that the point needs to be blue and red at the same time and be able to send the light out in a specific direction.
To become perfectly invisible, you would either need to be able to:
3 is easiest and one is impossible (of course), but 3 will never be perfect as:
a) No light receptor is an infinitely small point, so the image you present will have to be for a mean position.
b) Many light receptors (like eyes) have two viewers so as to be able to distinguish depth, so this requires you to present on the same side two images that are broadcast directly to the two input sources so that depth is still perceived–but that means that your emitters (pixels) are going to be split with only half of each going to the eye, meaning that half of it is dark. You might be able to bump up the brightness level to correct for this, but if the viewer got close enough he would be able to discern the dark spots. There would be similar “blank” spots necessary for your light receptors so you knew what to broadcast on the other side.
c) You would need to be able to be able to track all light receptors as they and you moved so as to make sure you’re broadcasting a properly tailored image.
d) You have to cart around a shield of receptors and transmitters, plus have a battery for it, and be able to do this without being heard or touching the ground.
2 would, I think, require finding some material that had this particular property and was sufficiently perfect that there would be no light loss. Of course, you wouldn’t be able to see anything outside the bubble surrounding you. And again you would need to cart around your bubble without making sound or touching the ground.
Well, you’d have to prove you came up with it before the latest James Bond movie. He had a car the could be cloaked using the exact technology you discribed.
Isn’t this essentially what a hologram does? ie reflect a different image from the same spot depending on what angle you look at it.
And, for Sage Rat’s point 3b doesn’t a hologram present a slightly different image to each eye ?
There’s a very interesting effect that occurs when you place a transparent object in a liquid having the safe refractive index. Ideally, it should vanish. In the real world, this hardly ever happens. There are several interesting effects:
1.) In general, although you can get the refractive index to match at one wavelength, it won’t match at all wavelengths (the substances are said to have different dispersions). Where the indices precisely match, you will get good transmission (not perfect – see below). Elsdewhere, you get scattering. The unexpected result is that you can see through in a direct line , but only in one color. Around the central region you get a sort of rainbow halo. This unexpected result is the Christiansen effect, named after (I kid you not) Christian Christiansen of Scandinavia. They used to use this effect for making bandpas filters, until they perfected optical coating techology.
2.) Even if you match the indices for several wavelengths, you still don’t get perfect transmission. Cal speaks from experience here. Although I could get solid lumps to “disappear” in a round container, if I put them in a flat-sided container with index-matching liquid, it would seem transparent only really close to an object. The farther away you got, the more translucent it appeared. If you were several inches away from a background object, it was like trying to see it through waxes paper.
Why?
Several reasons. For one thing, when you break up your solid material into many pieces, you almost invariably have some index variation from piece to piece. You get variations in bulk index, or the method of breaking it up causes stress birefringence. You get coatyings of dust or oil. Furthermore, small index differences don’t mean much at near-normal incidence, but as you approacj grazing incidence, even a tiny difference in refractive index will produce a noticeable optical effect. This is really the basis of the Christiansen effect – crumble up your solid phase into enough pieces and invariably you’ll have a lot of grazing incidence reflections causing scatter. In practical termsd, if you’re trying to be an invisible man in the fashion H.G. wells describes, by making yourself transparent with matching index, you’ll still be visible around the edges. Your skin will present a rainbow-like sheen around the edge. So will all your internal organs. You’ll look like a walking, iridescent Visible Man.
And that’s even when you can keep yourself from being covered with dust or water or paint.
Finally, a lot of substances have different refractive indices along different directions, and there’s nothing you can do that will match both directioons at once. You can see this effect with paper that’s got a drop of oil on it. The oil matches the refractive index of the cellulose fibers in the paper better than air, so you can see through the paper a bit, especially when it’s in contact with something. But you’ll never get it perfectly transparent. Even if you match the index in one direction in the cellulose fiber, it’s different in the other direction. (On top of which paper has sizing elements in it, bleaching agents, and often coloring agents as well. )
Incidentally, this is also the principle at work in a wet T-shirt contest. C’mon, this is the Straight Dope, we need practical applications.
As an aside, has anyone ever come up with a plastic which is closely matched in index, dispersion, etc., to water? It seems to me that such a substance would have many uses in novelty devices.
I’ve brought this up in the past. Unfortunately, since the object has to be very close behind the cloth in order to be visible, this means that the shirt would have to adhere to the object underneath. This is aesthetically unpleasant. Although, it should be noted, the fact that the cloth is wet would help it adhere.
Most plastics – most solid substances, in fact – have indices higher than water’s 1.33. I think a couple of fluorocarbon plastics might get down that low, but most of them aren’t transparent. Beryllium Oxide glass can be made with an index that low, but BeO glass has much the same effect as BeO, which is as bad as pure Beryllium. Not something you’d want near your lungs.
Ach, the British had it sorted in 1970. HM GOVERNMENT, PUBLIC SERVICE FILM NO. 42.
For whom?
