O.K. other than argue about psuedo science and the unsound theories of time travel… (as if any other theories so far are sound)
I thin I got something that might work… earlier someone said something about the difference of invisiablity and jsut plaind not being seen…
well think of the defenition of invisability… visability is what you can see… and invisability is without being seen…
so instead of looking of ways to hide things…lets think about ways to and the prefix “in” which means without to “visability” which means what you can see
Without sight is what we should be working on here
Sorry, no. something that is “invisible” is something that CANNOT be seen, not something that simply ISN’T seen. Conversely, just because something is visible in general doesn’t mean that YOU (or any given person) can see it.
Consider a sniper in a tree. The foliage hides him from his target; does this make him invisible? No - it simply makes him unseen. Similarly, the ninja’s vaunted ability to become invisible can be attributed to misdirection - e.g., using flash powder or a smoke bomb (or even a shuto strike to the bridge of the nose) to render someone temporarily unable to see, then moving behind them or around a corner before their sight returns. Not really invisibility, even though the end result is similar.
I prefer the explanation of the magic spell used in Barbara Hambly’s Time of the Dark trilogy. I’m quoting from memory so cut me some slack. The conversation was between Ingold, a wizard in another world, and Rudy, a man from our world that has been drawn into Ingold’s world and subsequently became Ingold’s apprentice.
Ingold says something like, “True invisibility can’t be achieved. What we do is much simpler. Surely you’ve had the experience of not seeing someone - maybe you dropped your keys, or were distracted by someone calling your name, or closed your eyes while you sneezed. It’s very easy to arrange for that sort of thing to happen.”
Rudy replied, “To all of them at once?” The thought of such a collective lack of attention staggered him.
The closest we are likely to approach the goal of being being “unseen” (forget the OP’s question of invisibility for a moment) is some sort of “reactive” clothing or fabric that can change color, and possibly texture to a degree, based on data it collects about colors and textures in the immediate surrounding environment. This would most likely involve an array of optical sensors throughout the clothing and AI interface that would tell the reactive cloth what to do.
It obviously wouldn’t be perfect but if you could make it small, durable and inexpensive enough it might have some practical merit for soliders in the field.
Research into these intelligent fabrics by Dupont et al is a lot further along than many people realize but we’re still some dsistance from even the “reactive fabric” system described above.
Take a person and stick them in front of a regular background, say a metre in front of a brick wall. Now, take a photograph of a 30cm x 30 cm bit of the wall and print it almost full size. Stick it on their chest.
From a single viewpoint and distance, the photograph will appear to be a continuation of the wall and the guy will have a “hole” through his chest. But if you change the distance, the sizes won’t match and the brick pattern will be too small.
Now, if you replace the photograph on the guy’s chest with a hologram of the wall with an image depth of 1 metre, he really will appear to have a “hole” in his chest, from all distances and angles. You’ve made a chunk of him “invisible”, as long as he doesn’t move.
This is where it gets tricky. Holographic film, as I understand it, is very high resolution photographic film. It records an interference pattern between a reference beam and a reflected beam, rather than recording a real image. So something like a liquid crystal display on an incredibly fine scale could give you a “controllable” hologram. (Visible light goes down to about 400 nm wavelength, which is 0.4 microns, whereas the current pentiums use circuits of 10-20 microns, so we’re going to need a factor of 10 improvement in miniturisation to build this thing. I have no doubt that will be achieved, although whether you could make a LCD on this scale is another matter…)
So, now we stick a few cameras on the guy’s back and a flat holographic movie screen on his chest. The cameras gather information as to what’s behind him, a monster computer calculates the hologram required on his chest to match the background, and the guy now has a permanent “hole” through his chest - he can walk away from that pesky brick wall.
Now you take a flexible holographic screen and build a suit from it, stud it with very small fish-eye lens cameras, build in a computer which makes code-crackers weep with envy, and you have something fairly akin to the Predator suit. Technically enormously difficult, and there’s probably much better ways to achieve the same effect, but I’m sure it’s doable. Might have to wait a few decades though!
Actually, I saw such an experimental suit on the Discovery channel or something. Its basically an suit that uses fiberoptics or something to color the suit the same color as whats behind it. It doesn’t make you invisible but it does make you pretty hard to see. Theoretically, the more ‘cells’ you have on the suit, the better it would recreate the image behind it. Problem is, a person is curved so the image would be distorted. The best you could hope for is to look like the Predator.
peewee_RotA, what is you, ignant?
The Superfriends and Lex Luthor are fictional characters created by writers.
Also fiction created by writers. Also irrelevent to invisibility.
Mirrors are delicate and do not survive battlefield conditions very well.
So now you are invisible to the naked eye but visible to every thermal sensor on the battlefield.
Thats ok. Science believes in you.
Astrology, ESP, palm reading, religion, reading chicken bones are all forms of psuedoscience. Go ask your high school science teacher what the scientific method is.
Not sure what to make of this incoherent, illiterate rambling, but I’ll try…
Speed, color, and temperature are not ‘dimensions’ in the traditional sense of the word. Two objects can never have the same x,y,z position in space at the same instant of time (t). You can’t make those objects occupy the same x,y,z,and t by changing their speed or color. Four dimensions.
There may be others that we can’t perceive and certain theories about the start of the universe predict that there are, but speed aint one of them.
In any event, you seem a little yong and ignorant to have such a strong oppinion on so many things.
I was having this discussion with some engineer friends of mine one time – we came up with the “cube 'o invisibility”, the Predator suit, and a few others.
The suggestion that really stuck out in my mind was that if you could generate a few magnetic monopoles, you could warp the light around you in such a way that you would appear not to be there. I guess that you could tie the monopoles down with some massless, frictionless rope while you were at it, but I thought it was a neat idea anyway.
"if you could generate a few magnetic monopoles, you could warp the light around you in such a way that you would appear not to be there."
As I understand it, monopoles are the hypothetical units of magnetic “charge”, analagous to the electron. Currently we generate magnetic fields with moving electrons, and electric fields with accumulations of static electrons.
From the symmetry, you could generate magnetic fields with accumulations of monopoles, and electric fields with moving “currents” of monopoles. But we have no evidence that units of magnetic charge exist.
Anyway, all they will give you are magnetic fields. Granted, you can get fields with radial spherical symmetry, which we can’t do with electromagnets, but I don’t see how this would turn you invisible. Can you give any more details?
"I guess that you could tie the monopoles down with some massless, frictionless rope while you were at it"
Either this is your way of saying monopoles don’t exist, or I’m really missing something…
I don’t know what it is about this thread but whoa! It’s like half are fighting ignorance and the other half are reveling in it!
You can’t be colder then absolute zero for the same reason you can’t go slower then 0 units of length per units of time. Basically what is means to be absolute is to be two numbers subtracted from each other, which is often called a delta this, or delta that, and then placed between the old absolute value bars. Absolute value being a truely magical thing. Check this out. The absolute value of 5 - 3 equals 2. And the absolute value of 3 - 5 also equals 2. Just think of that Groucho Marx bit. Matron says “Closer! Closer!” Marx replies "If I was any closer I’d be in back of you."I wonder if they got the absolute in absolute temperature from the absolute in absolute value. I bet they did!
Invisibility is a really tricky thing. I’ve always scoffed at what Star Trek and other Sci-Fi story lines called invisibility since I could always quite easily see the little distortion caused by their cloaking devices. Even the predator, I bet a properly trained computer would be able to pick it out the second it moved with only visible light.
But to be truely invisible what you’d have to do is to fully absorb each and every photon that hits you, and in the process record as many of it’s properties as possible. I think you have to do this with computers since I believe many lens and fibre-optic suits wont be able to handle really acute angles of insidence. Let’s assume we have the technological capabilities. Once you’ve absorbed the photon you’d then have to emit an identical photon to take its place on the other side of the body. Now if you were able to do this you’d be almost completely invisible, there’d still be that slight time delay from when the photon would have left your body, had you not been there, and when it was emitted. Hopefully if your computing power was powerful enough it would be very very small. Although a properly trained computer might still be able to pick you out when you move.
Oh, and you’d also be blind so you’d have to have small screens in front of your eyes which your on-body computer would make yet more photons to make a display screen so you could see where you are going. It would also probably be pretty hot.
So now we can try and go ahead and calculate the computing power necessary to deal with this huge amount of data needed to make you practically invisible to the outside world. I was able to google on “sun photons per” and got us this 3.8 * 10^21 photons per second per square meter of reception area. And here’s a neat site from Pediatric Critical Care Medicine that gives me a body surface area of 2.24 m[sup]2[/sup]. Which means that if I were bathed in the light of the sun I would be hit by 8.5 * 10[sup]21[/sup] photons per second. But let’s cut that by a little over half since the sun only shines on one side and make it 4 * 10[sup]21[/sup] photons per second that would have to be handled by computer. Now you’d have to know the trajectory of the photon, it’s point of entry on your body and it’s wavelength and that should bump you up to about 1.5 * 10[sup]22[/sup] photons per second which is essentially 1.5 * 10[sup]22[/sup] calculations per second.
There was a BBC article recently about a US supercomputer that we hope to finish by next year which will give 13.6 million calculations per second. Do Calculations per second follow Moore’s Law? If they do then and we can do 13.6 * 10[sup]6[/sup] calculations per second in 2002 then we should reach 1.5 * 10[sup]22[/sup] in oh … around 47 million years from now.
There’s probably something wrong with those calculations, but suffice it to say it would be a very long time from now and it is very doubtful any computer will ever be able to do that many functions per second. Maybe if it were the size of a small moon, but then the time delay would surely give you away.
So I’d say invisibility will never ever ever be something we could realistically enjoy and that … hey? Where did everybody go? Helloooooooooooooo!
Jinxie: nice analysis! What you are describing is photon-perfect invisibility, achieved by processing ALL the information contained in the incident light upon a person. Very tricky!
You can simplify the problem a little, however. You don’t need to be photon-perfect, any more than a photograph has to be printed with a million dpi resolution. Once you’re good enough that the eye can’t tell the difference, you can stop. Also, you don’t have to update your light emmision much faster than the human persistence-of-vision refresh rate. Rather than exactly reproducing each photon individually as it lands on one side of you, why not average all the photons landing on each 0.01x0.01 mm area, over one millisecond, and emit an approximation on the other side for the next millisecond? I’m sure we could cut down our development time to ten thousand years!
Also, consider the following challenging device: a plane surface which absorbs 100% of the photons which hit it, along with complete information as to their wavelength and trajectory. It re-emits identical photons almost instantaneously, at such angles as to reproduce a virtual image of everything, located exactly as far behind the plane as the real objects are located in front of it.
In terms of computing power, this device requires the same sort of order of magnitude as your theoretical invisibilty. But exactly the same result can also be achieved by the humble, low-tech mirror!
I don’t know if true invisibility or the partial “predator suit” invisibility can be achieved by purely optical means, but I’m absolutely certain there are more elegant approaches than the one I posted earlier, and I’m fairly certain the “predator suit” level of “invisibility” will be achievable some day.
matt, I think you are essentially correct. For some reason, my friends believed that you would have interesting control over electromagnetic waves in general once you had an operating monopole, and that you could essentially “wrap” light around you – more or less moving it out of your way. (I’m not really sure why they thought this, as it’s a little out of my depth. Also, I guess you’d be blind in such a field as well.)
I’m sorry if the joke about the physics rope didn’t come through. I don’t think there’s anything that specifically forbids monopoles from happening, but the general consensus is that it ain’t gonna happen. I mentioned it as sort of a fanciful suggestion.
As my advisor puts it, we know that monopoles exist, there’s just probably a very small number of them, like zero.
I very strongly suspect that it’s possible to construct a spherical shell of varying index of refraction in such a manner that an object inside the shell would be hidden to all non-radial lines of sight… But this isn’t any good, either, since you’d be able to “see” the shell from its refractive effects. Well, I shouldn’t say that it isn’t any good, since at the least, it’d be an interesting novelty device, but it wouldn’t be invisibility.
Good thing I looked at both pages. I almost used this quote but I forgot who coined it.
Anyhow:
If you go back in time 300 years and asked if it was possible to build a metal ship over 1000 feet long that weighed 75,000 tons and could cruise the seas for years at a time at 30 knots (like a nuclear powered aircraft carier, not even mentioning that the ship is designed specifically for launching and retrieving vehicles that FLY faster than the speed of sound) such a thing would be physically imposible. If such a ship was built, it could not carry enough sails or oarsmen to propel it. It would sink under its own weight. It would bankrupt whatever country tried to build it. Such a thing was impossible only because the technology wasn’t invented yet.
Is it possible to make something invisible? Sure, just make it look like the stuff thats behind it so perfectly that no one can tell the diference. Of course finding a way to do that cheaply and effectively is the tricky part.
Sorry I found this hread so late. A lot of the good and obvious answers ave been taken. But I’v spent a lot of timethining about this, and I’ve got a degree in Optics, so I as to add my $0.02
It’s easy to be invisible if you’re in the dark (and the people you want to not see you don’t have InfraRed viewers. This has been pointed out above, and by others Fredric Brown wrote a short short story where the punchline is that being invisible isn’t really an advantage in the dark.
It’s also easy to be invisible if both the background temperature and your temperature are so high that everything acts like a blackbody, and everything seems to be the same shade of red/orange/blue/whatever. To be invisible, just step into this blast furnace. It will work perfectly for as long as you’re alive.
H.G. Wells suggested (in The Invisible Man) that you can become invisible by making your body tissues transparent. You can’t acually do this, and even if you could, transparent doesn’t equal invisible. If it were, you’d have a hard tme seeing a glass full of water. As long as objects have different indices of refraction (air has one of 1.0003, glass typically 1.5, water is 1.333) you can see them, because you get reflection from every srface and refraction looking through them. So…
If you make something transparent and match the index of refraction to the surrounding medium, then you can be invisible, right? No, because…
If you want to be moving around in the air, you’ll have a hard time. To have an index as low as 1.0003 you’d have to be made of gas yourself. Solids and liquids have indices that are too high. Maybe you could send all your time in the water? Well, no…
Even if you match the refractive index at one wavelength of light, you probably won’t match it at all wavelengths of light. Refractive index changes with wavelength, a process called dispersion. In virtually all substances, the index drops as you go to longer wavelengths. The dispersion for gases dffers, in general, from hat it is in liquids, which is significantly different from the dispersion in solids. What happens when you dunk a solid but transarent object in a liquid which has he same index at one wavelength, but different dispersion? Something called the Christiansen effect, after its discoverer (I kid you not) Christian Christiansen. You see a colored outline of the object, because as you approach graing incidence you will no longer be matching the index. If you grind up your “solid hase” and mix it nto your “liquid phase” (as Christiansen, and later Rayleigh and Wood and others did) you find that you have built a monochromatic filter that transmits light at the wavelength where the indices matc. Elsewhere, you get too much scattering.
What if you find a solid and a liquid where you have not ony the same index bt also the same dispersion? Cal speaks from experience here – it’s virtually impossibe for them to match that well. I found two tha seemed perfect, bt when I put them together the result was not transparent – it was translucent.
OK, so you can’t index-match and become invisble. What about fiber-optic suits, or what about making something invisible by burying it in the center of a gradient-index material tha will “bend” the light around the object? Answer: It’s damned near impossible to design something that bends the light perfectly around an object as seen from all directions. About ten years ago there was an optical design problem proposed in which the designer had to design a “mothing lens” – a set of lenses that, when you looked thrugh them, looked as if there were no lenses in place at all. This turns out to be surprisingly difficult to do (and even to define as a problem). Let me just say that a plain slab of glass is not a solution at all. Some rather complex solutions were found, but none of them perfect. And this problem had a restricted set of viewing angles.
I suggested to someone working on a simila problem - make a “ball” of glass that had a varying index, with something inside that was supposed to be invisible – that thought you could solve that problem. The ball itself wouldn’t be invisible, just the object inside. The guy working on it eventually quit, convinced t couldn’t be dne. After all, something has to appen to the light reflecting from the object. (I suggest, still, that it will inded be present, but that you can “swamp” it with the rest of the system light, and minimize the amount of light reaching the object in the center.) In any event, this isn’t the probem you’re asking about.
One of the cutest resonses to the invisibility issue was given as the “twist” in a Marvel comcs story way back in the 1950s. The guy builds a device o ake himself invisible to the outside world, but finds that the outside world is invisible o him. This wuld be true. Not only couldn’t your retina intercept the light, but it would be swamped with light that should have been stopped by your sclera (which is now transparent). You woyudnt have an image even if that weren’t the case, because your cornea is now the same index as the air, so it has no optical power. Even the Lens of your eye which really does fine adjust, not major imaging) wouldn’t work. So an invisible man is blind. (Making your retina “have an imaginary index” is a sort of solution in that it will then absorb light – but that means it won’t be invisible any more. If you only mean for it to add a phase shift, though, you’re still blind. Besides, if your cornea and sclera are still indexmatched you’d be blind with or without an absorbing retina.)
It doesn’t elp to have a fiberoptic suit or gradient index surround – you still have to allow some light into your eye nd let it be absorbed there. You’re going to be a pair of walking eyeballs. As the sign on the truck mudflaps says, “If you can’t see me, I can’t see you.” Its true for invisibility, too.
