In Lineage Classic, the 'Invisibility Cloak' is an item that, when used alongside skills like Shock Stun and Triple, unleashes devastating power. Much like cloaking in StarCraft or Harry Potter’s invisibility cloak, it grants the cheat-like ability to hide from enemy sight—and believe it or not, this actually exists in the real world.

So, does this mean I can become a cool Dark Templar in real life and land a Shock Stun on my enemies? Let’s look at the principles and limitations.

※ My Own Lineage Classic Science' is a fun, curiosity-driven series where a reporter with a science background—but whose actual scientific knowledge has long since faded—uses AI to analyze the boundary between game logic and reality. Please keep in mind that this is just for fun, as there may be mountains of scientific errors. :)

= What is an Invisibility Cloak, or 'Cloaking,' in Games and Fiction?

In games, an invisibility cloak allows you to move as if your very existence has been erased, but in reality, collision detection remains active. It is literally just a 'state of being unseen.' In the real world, this is achieved through the 'refraction of light.'

Normally, for an image to form in our eyes, light must hit an object and reflect back for our eyes to absorb and perceive it. By manipulating the refraction of light, you can prevent an opponent's eyes from perceiving you. That’s right—if you can just manipulate light well enough, you can pull off a 'Poof, I’m gone!'—provided you can actually implement the method.

= The Real-World Invisibility Cloak: The Principle of Metamaterials

There is a real-world implementation of this principle, and it goes by the glorious name of 'metamaterials.' Ordinary materials have a positive refractive index; when light hits them, it reflects or is absorbed, allowing our eyes to perceive the object.

However, artificially created metamaterials can be designed with negative or fractional refractive indices, allowing light to bypass the object as if flowing around it. In other words, by bending the path of light, you can see through the object to what lies behind it, as if the object weren't there at all.

The theory of metamaterials, first proposed in 2006, has advanced to the point where cloaking has already been achieved in the microwave and infrared bands. It has even been published in Nature-affiliated journals. Of course, since the AI told me this, it could be wrong.

= But surprise! Actually, we can still see you

Here is where the problem arises. Did you notice the catch? It’s the 'microwave and infrared bands.' We distinguish and perceive objects because our eyes detect the reflection of light in the 'visible light' spectrum. Bending light across the entire visible spectrum is a technology that hasn't been perfected yet and is considered extremely difficult.

Furthermore, transparency across such a wide wavelength is fundamentally limited by causality and the Kramers-Kronig relations. I’ve never heard of that name either—what is that even supposed to mean? Anyway, to bend light paths simultaneously across the entire visible spectrum (380–700nm), you would need to manipulate the refractive index over a very wide frequency range, and this formula supposedly dictates that "absorption will inevitably occur somewhere." In short: it’s impossible.

Size is also a constraint. Current cloaking technology is limited to a few centimeters. Hiding a human body, which is measured in meters, is scientifically impossible. Science would need to advance to the level of magic.

= The Real Limit of Cloaking Technology: I Can't See Either!

If the points above are areas science hasn't reached yet due to technological limits, there is another fundamental problem with invisibility cloaks: you become visible the moment you move. Why do you think Dark Templars in StarCraft shimmer when they walk? Metamaterial-based cloaking is essentially a static structure. If you move, the shape changes and the cloaking effect breaks. This means it is impossible to implement cloaking with materials that flutter like clothes or a cloak.

An even bigger problem is that even if you overcome the limitations of a static structure, you wouldn't be able to see where you're going. This is the biggest issue. The whole point of cloaking is to refract light around the surface so the object isn't perceived, but this applies to the inside as well. With such a structure, no light would enter when you try to look out from within. If you wore an invisibility cloak, your game screen would just be pitch black.

What if you cut eye holes in the cloak? You’d end up looking like a monster with just a pair of eyes floating in mid-air. Oh... actually, you might become a Lord of Terror that way.

Besides, if it’s a cloak tailored to your body, any sword sticking out would be visible anyway. Even if the person is invisible, if a flying sword comes at you, wouldn't you try to defend yourself? An invisibility cloak that overcomes all these constraints to let you ambush an enemy is truly nothing short of incredible magic.