Why Is It Physically Impossible To Make An Object Invisible?

Invisibility in pop culture is a very widespread concept in many books, films, series or video games. The very famous Harry Potter invisibility cloak, the potions of the saga The Elder Scrollsthe One Ring of Lord of the Ringsthe optical technology of Predators or the optical camouflage of Metal Gear Solid. The examples are countless, and we have all dreamed at least once that this would be within our reach (for sometimes unorthodox reasons, but that is not the point).

At the risk of disappointing, making an object completely invisible remains impossible today ; we can camouflage it, blur it, but it will never go any further. It turns out that our colleagues from West France just published this article a few days ago, stating that “ a team of researchers has just reached a decisive milestone by designing a metamaterial capable of bending visible light around an object, making it undetectable to the naked eye “. This is unfortunately false, no progress has been established to date in the field of metamaterials for more than a year, and this article at no time cites a reliable scientific source proving its arguments. Harry Potter could never have hidden under his invisibility cloak: we explain why.

Total invisibility: science fiction

In 2012, a team from Duke University pulled off a sleight of hand, which they published in the journal Nature Materials…but which only worked with microwaves. A particular type of light, with a gigantic wavelength of several centimeters, compared to a few hundred nanometers for visible light: they are therefore easier to deviate.

The researchers had manufactured a metamaterial, a material specially structured to guide these waves. By sculpting it with perfectly ordered centimeter patterns (because they must be smaller than the wave they manipulate, which is several millimeters), they were able to ensure that the microwaves bypass a small object on which they had placed it, which camouflaged it.

Which therefore has nothing to do with being invisiblesince this camouflage was only effective for microwaves, for a microscopic object, and only at a single frequency. As soon as the object in question was illuminated in another band of the spectrum, it became visible again.

Three years later, in 2014, another study was published in the journal OPTICAL in which researchers demonstrated that a microscopic cylinder could “ disappear » if we projected on it a light adjusted to a single color, chosen to match the optical properties of the metamaterial surrounding the cylinder. Here again, it is impossible to speak of invisibility, the more appropriate term would be that of spectral maskingcar at the slightest variation in color, the cylinder reappeared.

Finally, in 2024, a team published work in the journal Science Direct on a carpet cloaka functional invisibility device… but only to hide a bump on a surface. The metamaterial does not make anything invisible in the air: it tricks the eye by making the light reflection identical to that of a flat surface. Impossible, once again, to make the object disappear in this way, since this just corrects the direction of the light reflection.

Three great unsuccessful attempts, which all share one thing in common: the fundamental laws of light prevent any notion of total invisibility from existing. For an object to truly disappear, each light ray that should strike its surface would have to be deflected in a perfectly controlled manner, then returned to the environment as if it had never encountered an obstacle. This requires maintaining exactly the same direction, the same speed, the same phase and the same amplitude for billions of photons arriving at different angles.

A material that never returns all colors identically, this is strictly impossible to achieve : we are talking about phenomenon of dispersion. A (theoretical) invisibility cloak should be able to reflect red, green, blue and tens of thousands of intermediate shades : it is therefore, therefore, impossible to build because it would violate the principle of causality established by Maxwell’s equations and Kramers–Kronig relations. These tell us that a system capable of returning all light frequencies without alteration should, in theory, anticipate how each photon interacts with matter. Anticipating, in this context, therefore amounts to violating causality, since the material should therefore know in advance how the light will interact with it: so this is what we call witchcraft. For it to be able to deviate all the colors at the same time, certain light components would have to be travel faster than light itself…which is prohibited by the theory of special relativity. In short, it is not tomorrow, nor even in 1,000 years, that we will cheat with Einstein, Maxwell and Kramers–Kronig !