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

Sure. I do it all the time.

Clothing isn’t particularly important, nor is chemistry.

All you REALLY have to do is turn out the lights.

Depending on the circumstances and the amount of ambient light in the location in question, no one is going to see you.


Nah, invisibility is too hard. Effrafax of Wug, via esteemed author Douglas Adams, demonstrated this.

So what you need is an SEP field!

Here’s some additional information on this “invisibility suit”.

Being invisible is no problem for me. All I have to do is try to attract the barman’s eye when attempting to buy a drink in a busy pub.

Actually, for this specific example, there IS technology available to make the black dot invisible, and has been for severaql decades. You could make a hologram of the scene as seen through the black dot, then paste it on top of the black dot. Whatever angle you look at it, you will appear to see through the dot.

Alright, using current holographic technology it probably wouldn’t fool an observer, I’m just observing a principle of how it might work. The point is that a hologram displays different images for different viewing angles. It doesn’t need to ‘project’ light, as some people have been discussing, it can work on relected light.

So, for a stationary object, seen against a stationary background, it might be possible to make it semi-invisible, or at least to give the illusion of transparency. If you had a fairly simple solid, eg a cube, and every surface was covered by a hologram on plastic. It’d be kinda tricky to set up, but possible.

Making one that is movable, or against a moving background, would be a lot harder. You would have to find a way of re-making the surface to create a new image. That would take a great leap in technology, but who knows what tomorrow will bring.

I’m pretty sure I have an invisbility suit - no matter where I go, woman never seem to notice me ;).

Could just use the old tried and true invisibility stick.

what range are we talking about here?

I’ve seen efforts to camouflage tanks on hilltops against bright skylines using very bright white lights shining towards the viewer. With a full spectrum coming in your eye, you can’t discern any shapes or colours. This system actually works very well, but obviously wouldn’t work at close to medium range, and only works in limited situations.

Don’t forget that after all this millions of dollars of equipment needed to make someone invisible to the naked eye, a $5 pair of IR goggles will make them stand out like a sore thumb.

I saw this same thing a couple of years ago. On Discovery, or something like that. I remember thinking at the time that it was pretty impressive. No way it would work in an urban environment, but as I recall, the guy did blend in remarkably well in the wooded area. Alas, this question was asked before, and I still can’t find a link to anything remotly resembling what I saw before. But I’m glad to know it wasn’t just in my imagination.

I saw that Discovery Channel special, too. It was in the context of advances in law enforcement. Basically the guy wore a suit that mimiced the colors around him. He laid down in the grass and was effectively invisible.

Clearly, this wouldn’t work in an urban setting, but there you have it.

By the way, how do chameleons pull it off? Do they have photoreceptors in their skin that pick up the colors around them and send a signal to repeat those colors on the skin? Is this a strictly biological process, or is it biochemical? Can it be repeated in a lab?

There are precisely two ways to be invisible:

1.) Assuming that only visible light sensors (like people’s eyes) are involved, shut off all the lights. Neither you nor the background can be seen in the dark.

2.) You need to heat your environment and yourself up to a sufficiently high temperature so that you and the background are essentially equally emitting black bodies, and all contrast is lost – everything will look a uniform color. Unfortunately, the temperature required to do this will make you severely dead. But you (or what is left of you) will be invisible.

All other proposals are unworkable. As a few minutes thought will tell you, the idea of piping light around you or using tiny TV screens on the other side won’t work – it effectively turns you into a walking billboard, and billboards are only “invisible” when seen at the correct location relative to the background (think “The Leap from the Lion’s Head” in Indiana Jones and the Last Crusade). The closest I’ve seen to that idea was an idea for a “crystal ball” that used gradient indices to warp light rays around an object in the center. Some scientists think that even that won’t work. I think it could, but at best it would make an item invisible when it sat in the center of a perfectly visible transparent ball – not exactly what most people have in mind for “invisibility”.

If you want your crystal ball to work from all directions, I think you’d have a hairy ball problem. An incident ray coming from any direction would have to be deflected tangentially to the surface (at least with a component tangential to the surface) in some direction; that gives you a “hair” at each point on the sphere. But there is no continuous nonzero vector field on the surface of a sphere, or, in other words, you can’t comb a hairy ball smooth.

Or look at it the other way: What would the view be from the inside? You’d get no light from the outside, so the inside would have to just reflect (possibly distorted) the interior. How do you construct an omnidirectional mirror just from varying indices of refraction?

There is a picture of the suit here:

“Retro-reflectum” sounds a bit Star Trek to me, but there you go.

While I recognize you’re being somewhat facetious about blackbody temperatures, it does bring up a major problem with so-called invisibility: infrared.

Yes, it is conceivable that a means of effectively camoflaging someone to the naked eye could be engineered. My system works like this: A small drone is quietly dispatched to the point of view from which you want to be unseen, say a guard post of some kind. This drone, which must be small and silent enough not to be detected, takes up a position on top of or immediately next to the (let’s say) guard post and images the area you’ll be traversing. (Better yet, you have two drones set a small distance apart for the parallax.) You can then walk unseen across the imaged area wearing a suit with some sort of light generation system, fiber optics or something else that doesn’t exist yet, that replicates the image seen by the drones. It’s basically the same as the projection system already described, except it generates its own image; it’s more like point-specific rear projection than front projection. Assuming enough computer power to keep track of where you are in the environment so as to generate the correct part of the overall image, and assuming the indistinguishable-from-magic technology to create an image-generating suit is developed, this would actually work pretty well, I think.

The problem is that you’re still a fairly substantial source of heat, and there’s really no way to camoflage that. It would be difficult during the day to blend your body heat in with the environment, and damn near impossible at night; you’re still a big ol’ blob on the guard post’s IR screen.

So this kind of system might work fine for a high-tech assault on a low-tech target, exactly the same as many of our military operations in the third world are today, where you’re defeating the enemy with a vast gap in technological capability as much as with arms, but anybody who can afford an IR setup will see right through the false image. It’d work just fine to fool the young conscript sitting on a rock with a pair of binoculars, but not much beyond that.

I’ve read this several times, and you’ve lost me on the first part – I’m familiar with the Hairy Ball problem, but I can’t see how it applies in this case. Al;l I have to do is direct the light around the object – ideally, it should come out in a “mirror image” direction, but as long as I just want the object in the middle not to be seen, I don’t really care too much about exactly where or how it comes out, as long as it doesn’t intersect my object.

And it’s not true that I’d get no light from the outside. If my index variation is radial, then rays coming at normal incidence ought to go right through to the center. Admittedly, my object won’t be truly invisible, since a line of sight down a radius will “swee” my object (and light that reaches it will be reflected and scattered elsewhere). But my feeling is that the light from the object will be so mixed up with random rays from other directions that you wouldn’t make out the object in the center.

Just don’t take the crystall ball into a dark room and put a flashlight right up against it. All bets are off then.

Not being facetious at all, in the sense that this can be a problem at very high temperatures – you can lose things in a very hot furnace. Or, it can be an advantage – a hole cut into a hot blakbody is the closest thing you get to an ideal Lambertian radiator. And if it’s hot enough, the internal geometry doesn’t matter.
I bring this up in part because th movies get it grotesquely wrong. In the film Hardware a woman hides from an IR-seeking robot by hiding in the refrigerator! This makes as much sense as hiding a candle in a dark room – you’ve actually increased h contrast and made the thing you’re trying to hide more visible. I don’t think the “coat it with mud and it’ll disappear” solution used by Arnold in Predator would work, either. They did get it right in Tremors II, where they guy “disguises” himself from the ambulatory IR-seeking Graboids by coating himself with a layer of frost. Untiul it melts, of course.

Chronos – I think that your “hairy ball problem” is the same as my “no invisibility at normal incidence” problem. But if the crystal ball has, as I say, radial symmetry (and I find it hard to imagine fabricating it any other way) you have that “hairy ball problem” at every point on the sphere – the normal always gives you a straight shot to the center. But I never said this gave you invisibility – just the closest thing o it. As I say, I expect that the light reflected from whatever is at the center will be lost amidst the refraxcted light from elsewhere. If you assume non-radial gradients, then you could always put your combed-to spot on the bottom or something.

For cryin’ out loud, I’m describing something ere infinitely more likely to work than James Bond invisi-suits or -Aston Martins, and you’re complaining that it’s not perfect?

:smiley: Good point well made. I love humans. We’re so stupid and so clever at exactly the same time.

I think I saw the tv programme someone else has mentioned above, in which a practically effective invisibility thing was constructed. iirc it was one of the Open University science shack things, and they were trying to find a way of making the bloke become invisible. They tried mirrors and different ideas. Basically it didn’t work but they got closer than one might have expected. If you weren’t LOOKING for someone hiding, he might have got away with it.

Here’s a link about the show: Looking for - OpenLearn - Open University

There’s also an OU discussion of the show here - - with an interesting link or two.

Well, from reading all these cites it seems that the inventor’s ideal use of the technology is for objects that don’t walk and talk, like a pseudo-window, or transparent floors and fenders. So while the technology was demonstrated on a human, it seems that it would certainly be more practical in non-military application.

And not to nitpick, but in relation to the OP, as soon as you put on some IR goggles, your eyes aren’t really naked anymore, are they?