Is it possible to make someone invisible to the naked eye?

I heard about an ‘transperancy suit’ a little while back, not sure if it was real or not, but it does sound interesting. I was just thinking, is it possible to make people appear invisible, using clothing or even a spray on chemical or anything, theoritically?

The “transparency suit” used input from a camera to display the scene behind the person wearing it. As I recall, the media demonstration was actually a bit of a con, as the photograph was taken using a camera that combined the images electronically. To the naked eye you wouldn’t see the effect… However, in principle, if you had lots of inbuilt cameras and some decent processing power and image-display technology, you could make things pretty much invisible, if the suit itself acted as a screen. The car in the Bond film The World Is Not Enough was supposed to use this technique, I believe.

Forget about mystical chemicals and sprays, though - people are solid and absorb light. You’re not going to get around that, other than with some kind of projection/imaging device.

AFAIK, the main problem with such a thing, even theoretically, is this: Whatever procedure you’re going to use (causing light to go through the person, or to go around the person) your goal is that someone looking in your direction should see past you, whether you’re there or not. This means that he will receive all the light waves that he would get even if you weren’t there. That means that none of those light waves get to your retina. That means that even if you could do it, you’d be effectively blind.

Even this would only work when viewed from a specific angle - in order to make a proper invisibility suit, you’d have to intercept incoming rays in all directions and emit them from the opposite side in the same direction as if they had traveled straight through - this is further complicated by the fact that ‘the other side’ might at one moment be your arm and the next moment, the side of your abdomen, if you’re on the move.

Another thing worth pointing out in the case of a “transparency suit” is light intensity. If the suit somehow emitted light much like an LCD screen or some other technology, it would have to match exactly the intensity of the light in the surrounding environment. Daylight would be very hard. If you could work out the viewing angles and other major roadblocks as pointed out by others, you, appear as a MUCH dimmer man-shaped silhouette. Unless it was simply some kind of fiber optic type suit, I think any kind of projection technology would be out of the question.

This is only a problem for passive systems. Not a problem for active systems.

For example: a sensor detects photons coming from a certain direction. It then splits the signal, sending half to the user’s eyes, and the other half to emitters on the opposite side. But, instead of emitting the half-intensity light, use an amplifier to bring it back up to the original intensity. And there you go.

This technology does not exist, AFAIK. Big issues would probably be things like maintaining polarization and coherency (or lack of those). Power consumption and removing waste heat would be big problems too.

Yes, and no.

No in that there is no practical way to bend that much light to make complete invisibility.

Yes, in that common (and uncommon) camouflage techniques can reach level of practically invisibility under certain circumstances. It would be easy to characterize such techniques as mere party tricks.

Fair enough, but it is as close as we can get to invisibility.

Think about what would actually be necessary to make a Predator-style invisibility device; each point on the suit must capture information about incoming light from every direction, the corresponding point where each of those captured rays should emerge (which will be different for all of them) must be calculated and a corresponding ray emitted at the right intensity and in precisely the right direction - the amount of information that you’d have to process to achieve this is absolutely unthinkable, not to mention that the hardware to capture and emit the rays would be incredibly hard to build.


Nitpick: the Bond film that had this car was Die Another Day.

Currently, processors couldn’t handle that kind of load. Processors of the near future, however, should be able to easily handle it, if technology progresses as fast as it has over the last 20 or so years.

I think it’s the actual image-capture and display hardware that will be the difficult part. Somehow, each “pixel” on the suit will have to be capable of capturing an image–in multiple directions and, simultaneously, display multiple images captured from the other side of the suit.

Specifically, consider a pane of glass with a black dot on it. Three people are standing on this side of the pane, looking at the dot. Each person will see that dot covering up a different part of the colorful background behind the pane. For that dot to appear transparent to all three people, it would have to display a different color to each person (technically, it would have to display six colors, one for each eye viewing it). I know of no technology that can display different images, for different viewing angles, that would be uselful for the project we are discussing.

In theory you would need a suit covered in photon detectors that could detect not just the quantity and color of each photon that struck them, but also the direction that each photon was coming from. The suit would also need to be covered with emitters that could emit any color of light in any direction. The size and spacing of the emitters and detectors would have to be very small in order to achieve a resolution that would fool the human eye from close range. You would also need a very powerful computer (by modern standards).

The detectors would record the color and direction of each photon and relay that information to the computer. The computer would determine the “exit point” of the photon if it had passed straight through your body, and what direction it would be going in. The computer would relay this to the appropriate emitter, which would send out the “fake” photon. If this were done fast enough, an observer might not be able to tell that you were there.

All of this would have to be done fast enough that there’s no noticable delay in the retransmission, even if you were moving rapidly in relation to a fixed background. For example, if you were a passenger in a car going 90 miles an hour and the driver looked through you at a window behind you, you wouldn’t want the scenery behind you to be out of synch with the rest of the scenery. Of course, a computer fast enough to pull off the deception would also be fast enough to see the inevitable lag. Someone could devise a set of goggles which would reveal your presence using the same technology. Similarly, if your only requirement is that it makes people invisible to the human eye, you would presumably ignore colors of light outside of the humanly visible spectrum. Someone wearing infrared goggles would certainly notice you as a big black blob. Finally, the uncertainty principle would keep you from being able to create a 100% accurate facimile. It’s doubtful that the difference would be noticible to the human eye, but it would never be quite “right”.

Incidentally, if you designed it right, the computer would be the only thing that draws a significant amount of power. Since you’re goal is to broadcasting exactly as much energy as you’re absorbing, you would only need enough power to make up for the mechanical losses of of the detectors and emitters. If they were very efficient, that might not be an inordinately large quantity.

A video projector is a device that emits different color light in different directions. What you are describing can be achieved by an array of tiny video projectors. So it’s pretty simple in theory; it’s just a matter of miniaturization and data processing. I expect the most difficult part is the creation of tiny, incredibly bright light sources for those tiny projectors.

If we’re talking about a flexible suit, the determination of the appropriate exit point is the really tricky bit, consider: there’s movement and rotation of the body, movement of the limbs and distortion/flexing of the suit fabric to take into account - at any given moment, the distribution of exit rays would be different from the previous - when you move your arm, some of the rays that were being emitted from your torso now need to be emitted from the arm that obscures that section of torso, but from other directions, that section of torso is still visible, but the suit fabric has puckered, so the angle of emission of all the rays from that section needs to be recalculated.

The computer would have to know the absolute position and absolute orientation of all the receivers and emitters.

Deciding to make it a rigid spherical shell of invisibility, rather than a suit, would make it vastly easier, although less practical for the user.

I don’t understand. Every video projector I know of projects light in one direction only, usually at a screen. I don’t see how one projector can project one single “pixel” and have it be red on the north wall, blue on the east wall, white on the ceiling, and green on the floor.

OK, I over-simplified a bit, but the principle is the same. A video projector can project red light into one corner of the screen and blue light to the other corner, or any other arbitrary pattern. Normal video projectors have limited beam width, but if you add a fisheye lens it should be possible to widen the beam to 180 degrees. A miniature Omnimax projector, essentially.

One thing that such a theoretical device would have trouble with is emulating a black background when the wearer is standing in an illuminated area - walking past a black building on a sunny day, for example.

Incidently, I saw a televised demonstration of a suit similar to one mentioned (may have been the same one, not sure) and, although it did not render the wearer invisible, it was very effective at camaflouging (sp) him. This sort of technology would be very effective at this task, even if true invisibility would not be possible.

OK, that makes a little more sense. But it still seems to me that such a fisheye projector would need to project a pixel in an unlimited number of 3-dimensional directions at the same time.

For example, if I’m standing directly in front of a projector, my eye should be within the projection beamwidth of one pixel. If I move two inches to the right, I should be within the beamwidth of a different pixel. And every two inches that I move, in two dimensions, should bring me into another beamwidth.

Each point on the suit would be projecting a full 1000 x 1000 (for example) grid into space in 1,000,000 different directions per pixel. An effective suit might need about 10 of these projecters per inch.

The amount of sophisticated hardware and processor power needed seems quite staggering. But, I do see, now, how it can be done.

I did a thought experiment that may be applicable. Take a hollow sphere and fill the surface with pinholes. Each hole is a pinhole camera projecting its image on the opposite inside surface and. An observer looking through a hole on the near side sees through a hole on the opposite side, seeing the object past, not the sphere. This happens for any pair of pinholes in the sphere. Now let’s add electronics to do the distribution that geometry provided for the pinhole cameras and allow time slicing so each “cell” on the surface acts as a camera first then as a projector. We no longer need all the space inside the sphere because we’re distributing the pixels of the image of each camera through cables just under the surface.

I’m not saying there aren’t insurmountable physical hurdles but there is a model for an invisibility suit.