Invisibility cloak which makes something invisible… We are sure it’s one of the superpowers that many want the most. It is one of the indispensables of science fiction and fantasy film creators.
Let’s first talk briefly about that famous story in Harry Potter: The Story of Three Brothers.
The Peverell brothers find Death. Death tells them he will give whatever they want to these brothers. The elder brother asks for the Elder Wand, which is a wand that will never lose in a duel, the middle brother for the Resurrection Stone to bring back the dead loved ones, and the younger brother for the Invisibility Cloak because he does not trust Death and wants to hide from him. Death grants their wishes. But reluctantly gives up the invisibility cloak for the younger brother. The younger brother, whose only desire is to hide and be protected, runs away from Death for much longer than his brothers. Later, Peverell’s invisibility cloak is passed down from father to son for generations and reaches our hero, Harry Potter. For those curious about the story’s details or want to remember it, you can find the “Tale of Three Brothers” scene narrated by Hermione Granger on YouTube!
Well, now let’s come to our main topic today. Is it really possible to make an invisibility cloak like in Harry Potter? Or is it just fiction?
Short Answer: It looks like we will, but it takes work!
Scientists and private companies have been working towards this dream for years. But to make a magical cloak, we have to push the limits of technology. So, how close are we to that goal?
In the early 2000s, researchers from the University of Tokyo created an optical camouflage system using a highly reflective material that makes anyone wearing it look like they’re not there. Of course, multiple versions of this technology have emerged and evolved since then. The movie Mission: Impossible – Ghost Protocol used a similar, but fictional version of this technology we mentioned.
The Most Important Feature of the Invisibility Device: Being a Light Bender!
Our greatest expectation from an invisibility device is that a person or object bends the light around it in all directions.
There were benders in the Avatar animated series, if you remember. Let’s consider his light-bending abilities. Scientists call this bending of light a refraction of light. The direction and angle of the light can also change as the material or the medium which the beam passes through changes.
We can easily observe this in daily life. Put a pencil in a glass of water. The pencil inside appears broken when we look atnt angles it from differe. However, this is, of course an illusion. We can think of the reason for this illusion as the resistance that light encounters as it passes through different media. This resistance is called the refraction index.
Each medium has a different index of refraction. Therefore, as the environment changes, the rays reaching our eyes begin to look different. Even the speed of light changes from medium to medium because of this refractive index. For example, we can say that light travels 1.33 times faster in air than in water. Now, let’s put the speed of light aside and return to the invisibility cloak.
One of the Most Realistic Options: Metamaterials
All substances in nature have a positive index of refraction. All the technologies we know are based on this positive index of refraction. If light causes an illusion that we cannot believe even when it passes into another medium, isn’t it possible to manipulate our perceptions and make something completely invisible? That’s precisely what scientists asked: the question’s answer is hidden in the refractive index. But there was a problem. To achieve invisibility, the refractive index had to be negative, not positive. This meant producing a different substance from all existing substances. And that’s how metamaterials were born.
We have started to hear the word meta very often lately. From the metaverse, where a virtual world has been created, we come across it every moment, just as the Facebook company has changed its name to Meta. Probably one of the most popular words of this century will be meta. We can translate this word as “beyond.” Metamaterial, on the other hand, can be thought of as “beyond matter.”
How Metamaterials Work?
Metamaterials are metal-dielectric composites designed at the nanoscale. This structure acts like a series of artificial atoms, allowing rays to pass freely around an object. In other words, the metamaterial directs light around the thing it covers, creating the illusion that the object is not there.
So, the logic of the invisibility cloak is just an illusion trick. Our aim is not to destroy an object or distort its appearance. Otherwise, for example, the frosted glass that many of us have in our homes also makes the objects behind them invisible or less visible. But we want something else. Simply, we aim to bend the light in front of that object so that it passes around it and fuses it behind. It might be easier to imagine this by thinking of cars driving through a roundabout.
How close are we to producing an actual invisibility device right now?
Right now, there are two main problems before we get the invisibility cloak :
The first is to achieve this invisibility in the “visible” part of the spectrum.
In 2006, a group of Duke University scientists used metamaterials to create a simplified invisibility device that could hide objects from microwaves. Yes, we have an invisibility cloak prototype. But this makes the rays of the microwave region invisible to our eyes anyway. It does not affect the visible area. So, with the naked eye, it doesn’t make much sense. While this step could not hide objects from human view, it was an incredible achievement to create an actual invisibility cloak.
Ten years after the first study, researchers at Duke University have developed a seven-layer metamaterial cloak that can shield a small object from infrared to radio waves to make it invisible.
This study, which took place in 2016, was also essential in creating an invisibility cloak that could be used in real life, although it couldn’t hide things from human view.
While these developments were fascinating, many were only valid at the laboratory scale. One of the most important companies implementing the invisibility cloak in practice was the HyperStealth Biotechnology company.
One Step Closer to Invisibility
You may not have encountered what we mentioned above a few paragraphs before. But, most likely, you have come across an article with this theme: “Invisibility becomes real! Hyperstealth. This product, which is currently being developed especially for use in the defense industry, is seen as the first step in making a person or even a military tank “invisible” by camouflaging.
The company achieves this high-level hiding technology thanks to the lens called “lenticular lens.” This type of lens refracts light according to the angle of view.
HyperStealth Biotechnology firm has found a way to arrange lenticular lenses to create “dead spots” at certain distances behind the material. In this way, when viewed from the front, we see only the background without seeing the object behind the material. This illusion creates the illusion of invisibility for us. Another good news is that the company can make this material as thin as paper. In addition, they state that it is cheap to manufacture and does not require a power supply.
In addition, HyperStealth CEO Guy Cramer states that the materials used to create invisibility technology have a huge reflective surface area so that they can be used not only in invisibility but also to increase the efficiency of solar panels.
Can We Say We Have Obtained An Invisibility Cloak Like In The Movies?
Not really. Yes, the work with Quantum Stealth and metamaterials is very promising. However, we cannot say that we have achieved complete invisibility at the moment. A result very close to invisibility was achieved, making it difficult for viewers to distinguish objects. However, unfortunately, this does not mean there is a technology to hide us “completely” as we see in these movies. As we mentioned in our article, the biggest challenge in developing an invisibility device that can be used in practice is that it has to hide many different wavelengths, including the “visible region” seen by the human eye. We still have a long way to go before we get to that level, but science tells us it’s possible.
“The invisibility cloak looks pretty fictitious, I know, but it totally aligns with the laws of physics…“ said principal research professor Vladimir Shalaev, an electrical and computer engineer at Purdue. “If we make it, it will definitely be like Harry Potter’s cloak. It won’t be heavy because there will be very little metal on it.”
It seems that we will soon be able to see the magic items that we say, “Oh, I wish we had one,” that we see in fantasy literature or science fiction works in daily life as well…
As Arthur Clarke said, “A sufficiently advanced technology is indistinguishable from magic.”
References and Further Reading
Alexander, D. (2021, February 19). Invisibility cloaks are no longer just science fiction. IE. Retrieved January 31, 2023, from https://interestingengineering.com/innovation/invisibility-cloaks-are-no-longer-just-science-fiction
Chen, W. T., Zhu, A. Y., Sanjeev, V., Khorasaninejad, M., Shi, Z., Lee, E., & Capasso, F. (2018, January 1). A broadband achromatic metalens for focusing and imaging in the visible. Nature News. Retrieved January 31, 2023, from https://www.nature.com/articles/s41565-017-0034-6
Invisibility cloaks are not just possible, but are becoming reality. Big Think. (2022, April 28). Retrieved January 31, 2023, from https://bigthink.com/starts-with-a-bang/invisibility-cloak-183582/
Researchers determine fundamental limits of invisibility cloaks. UT News. (2018, November 8). Retrieved January 31, 2023, from https://news.utexas.edu/2016/07/05/fundamental-limits-on-invisibility-cloaks/
Asu Pelin Akköse and Mete Esencan have done the proofreading.
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