Can invisibility be achieved through physics?

Question

I’ve been reading about the concept of invisibility in physics and am curious about its feasibility. We often see references to invisibility cloaks in science fiction, but what does physics say about it? Are there any existing theories or technologies based on real-world physics that might enable invisibility, even for a limited range or in specific conditions? How would concepts like light manipulation or metamaterials play a role in achieving this? I’m particularly interested in any potential scientific breakthroughs that could bring this concept closer to reality.

i have researched and get to know that Invisibility is theoretically possible, but there are some limitations. If a person were to become fully invisible, they wouldn't be able to see anything either, since light would be bent around them. However, there is a way to achieve partial invisibility using metamaterials. These are specially designed materials that can bend light around an object, effectively hiding it from view.

The problem, though, is that to make someone invisible, they would need special lenses in their eyes. These lenses would have to bend the light at a 90-degree angle, meaning only a small fraction—about 3% of the light—would be able to pass through. This could allow the person to see, but it would also reduce the amount of light they could perceive, making it much harder to be seen clearly but you can see other things because of that 3% light.

Answer 1

An internet search turned up this video about the Lubor's lens that is apparently used in magic tricks. It does a good job of hiding certain vertically aligned objects when there is an essentially horizontally aligned background, such as the red handles of the pliers in the screenshot of the video below:

The lens is a type of Fresnel lens that can be made as a thin sheet, with thin parallel vertical prisms. These smear out vertical lines horizontally such as the outline of a standing soldier and broaden out horizontal background lines such as the horizon or tree line behind so that they fill in the gap left by the removed images of the vertical objects. In the video you can see when the presenter is handling the lens, light sometimes reflects off it and this could give away your position if the enemy sees a flash or glint of sunlight reflected by your shield. Presumably the videos are made in ideal lighting conditions and the shield might not be perfect in real conditions, such as in the middle of a field on a sunny day. Possibly they can be improved by putting a non reflecting matt coating on the lens.

Another video shows how to make your own invisibility shield. This appears to work quite well! The presenter states he is using a type of Fresnel lens with micro lenticular lenses on the front. These are a type of lens made with material with different refractive indexes from centre to edge of the lens. That is the official definition of a lenticular lens, but here I suspect they mean a thin sheet lens that is composed of thousands of micro-hemispherical lenses. He claims the micro lenses focus light from the background behind the user around the user and towards the observer in front, as per the screenshot below: .

Here is screenshot from later on, when he is using it outdoors. Personally, I think it is not a bad result, especially if the viewer was further away and not expecting someone to be there.

P.S. You will come across videos with titles like "Chinese invisibility cloak" that appear to be cheating and using a flexible blue sheet and blue screen editing technology to give the appearance of an invisibility cloak in the video that you would not see in real life.

Here is a screenshot of a lenticular lens sheet you can buy on the internet.

Answer 2

You could do it with ordered fiber bundles. A fiber bundle is a bundle of thin glass threads. Light that enters each thread bounces its way down to the other end of the thread and comes out. So if you focus an image on one end of the bundle, you see the image at the other end. The bundle is flexible, so you can put the output where you want it.

Ordered fiber bundles come with a lens built in so the scene in front of it is focused on the end of the bundle.

A fiber bundle is typically a few millimeters across. But if you have lots of money, you can pack many bundles side by side.

So build two walls of fiber bundles and hide in between.

Answer 3

We can say the ability to "see" someone is related to the law of reflection: if a light ray coming in your direction hits you at a certain angle $\theta_{i}$, and if there is a observer at an angle $\theta = 180º - 2\theta_{i}$ from that original direction, it will see you. Hence, the ability to be invisible can be achieved with some ideas:

1. Light absorption. To be covered by a material which absorbs all radiation incident upon it would be one possibility. In order words, to be covered in the closest to an ideal "black colour" as possible. Obviously, your silhouette could still be inferred from the light reflection of your environment.

2. Playing with mirrors. That is already used even as a movie's prop: you can hide behind properly aligned mirrors that will reflect the general environment and simulate invisibility. This was done in a funny prank in the following video: https://www.youtube.com/watch?v=whJ8UFs_ujA

3. Using video equipment. You could do an advanced version of (2) by recording the environment around you and playing it simultaneously in a screen around you.

It is important also to comment that the popular definition of invisibility normally refers only to visible light. You could still show up in other types of sensors and detectors, such as radars, etc. There are also techniques to mess with them in some cases and be "invisible".

Answer 4

Fiberglass with a parabolic curve of refraction index has the property to be invisible at certain (periodic) lengths. Inbetween it can be used for other optical tricks, for instance encoded mirrors. But back to the invisible length. It works in all 3 dimensions, so there is no flatness like with a video stream, but it is really vanishing, so that if you go directly up to the protected area your viewpoint will be directly from the other side. For real invisibility you will need to add the distance back, probably with mirrors.