Modern metamaterials theoretically make it possible to make a person invisible, but in practice this is still very far away.
Recently, among the users of the Chinese segment of the Weibo network, a video that depicts how a person uses the "invisibility cloak" has gained viral popularity in a short time. It is interesting that, although from a scientific point of view this is quite realistic, at the moment there are simply no such perfect capes, raincoats and even hats of this kind in the world. Moreover, the video, which has caught the attention of tens of millions of people, is actually just a fake.
First, a little theory. What is shown in the video is theoretically possible, although even in the last century, physicists were sure that invisibility had a place only in the novels of H. G. Wells. The fact is that in 1967 Viktor Georgievich Veselago described the expected properties of materials with a negative refractive index.
The refractive index is equal to the ratio of the sine of the angle of incidence of light on the material to the sine of the angle of refraction of light in the material. If we take air, then its refractive index is very close to unity (however, in the summer haze it is higher), so it does not distort the outlines of objects. Already water has a refractive index above unity, and a number of optical glasses - even more. A material with a negative refractive index is an artificial metamaterial, the properties of which are determined by a specially created periodic structure in it.
First, a little theory.
Imagine a situation where we have:
- a person who wants to disguise himself;
- an awning made of metamaterial for this purpose;
Promotional video:
- an external observer.
What happens in this case?
The metamaterial allows you to make it so that damped light waves falling into it from one side (hidden from the observer) will add up and amplify. Thus, it will begin to “transport” part of the light from the distant background, obscured by the camouflage surface, outward - to an external observer. However, in this case, the metamaterial does not catch the light waves reflected from the disguised person - their source is closer than its specially tuned "focus of vision". As a result, such waves are reproduced on the side facing the observer (the opposite side of the metamaterial). This creates the feeling that, apart from the background, there is nothing behind the metamaterial.
However, like any optical device, all existing metamaterials are too crudely arranged for the substitution to be overlooked by the human eye. For example, metamaterials allow only waves with a certain length to "smoothly" bend around the cloaked object. Therefore, a person behind a screen of metamaterial can only be translucent, with a kind of glow along its contour in a certain range. To work even at such a modest level, the metamaterial must be located at a strictly defined distance from the cloaked object or person.
In theory, you can create a metamaterial with more flexibility in work, but in reality, before that, at least decades of painstaking work. The first scientific research in the Western world on this topic appeared only in 2007, and the first samples of metamaterials for the optical range were created (ibid.) Only nine years ago. Expecting metamaterials today, as demonstrated in a viral Chinese video, is the same as expecting an iPhoneX-class device to be produced from 1940s transistors.
What's on the video then? Zhu Zhensong, a producer for Quantum Video, told the Shanghai official Jiefang Daily (the local mouthpiece of the Chinese Communist Party) that the video was fake. “Software like Adobe After Effects, Nuke, or Blackmagic Fusion can edit the background and insert objects into it. Similar effects have already been used in a number of militants,”he said.
However, in reality, you don't have to be a filmmaker to suspect the fabrication of this video. The problem is that it has a number of minor inconsistencies. For example, with the gloves of the person holding the “invisibility cloak”. With the fact that behind the film, all the objects behind it are shown, except for the person, including the boards at his feet. A real "invisible" metamaterial, capable of transmitting an image of the background into the distance, but hiding nearby objects, would disguise not only a person, but also those inanimate objects (boards at his feet) that are at the same distance from the film as the masked person.
Finally, in the video only those background leaves are really moving, which we do not see through the "invisibility cloak". It is extremely doubtful that one and the same wind will sway some plants - outside the covering of the "mantle" - and not sway others, those behind it.
In short, we are just trying to get a viral video with a lot of views on a trendy and popular topic in the scientific world. Perhaps it is even useful for educational purposes. After all, what else, besides a viral fake video, can remind us of the prediction of a Russian scientist half a century ago?
IVAN ORTEGA