Invisibility!!!
Invisibility refers to the condition where an object becomes imperceptible to the human eye. An invisible object, therefore, is one that cannot be seen. This intriguing phenomenon draws the attention of both physics, exploring the underlying principles, and perceptual psychology, investigating how our visual system interprets such absences.
You've laid out a fascinating overview of invisibility! It's true that the most intuitive idea of being unseen stems from transparency – allowing light to pass right through. As you mentioned, while perfect transparency isn't found in nature, we see degrees of it all around us.
It's also crucial to remember that "invisibility" isn't absolute. As you pointed out, it's tied to the observer, whether that's the human eye or a specific instrument. What's invisible to one might be detectable to another, or even visible under different conditions. The idea of cyclical perception of invisibility in sensory research is a particularly interesting point.
And you're spot on about invisibility being the ultimate camouflage, going beyond simply blending in by eliminating any visual signature altogether. The shift to using other parts of the electromagnetic spectrum like radio waves, infrared, or ultraviolet to achieve a form of "invisibility" to the naked eye is a clever concept often explored.
Finally, framing invisibility as an "illusion of free space" in optics makes perfect sense. It highlights how our perception is being tricked into seeing what isn't there – or rather, not seeing what is there.
The way fantasy and science fiction explore invisibility, whether through magic or advanced technology, really captures our imagination and pushes the boundaries of what we consider possible. It builds upon these fundamental principles of light and perception that you've so clearly described.
Some effort done by scientists.
Fishnet metamaterial from stacked silver and metal dielectric layers
One approach, pioneered by Jason Valentine's team at UC Berkeley, involved constructing a "fishnet" metamaterial from stacked silver and metal dielectric layers with holes punched through. This material exhibited negative refraction in a region near the visible spectrum, relevant to fiber optics. Their design principle relied on creating structural arrays smaller than the wavelength of the light being manipulated. Another team achieved similar results in the visible spectrum by growing silver nanowires within a porous aluminum oxide template, with the nanowires spaced at sub-wavelength distances.
Separately, researchers at Imperial College London and Duke University, led by Professor Sir John Pendry, demonstrated an invisibility cloak for microwaves in 2008. This cloak concealed a copper cylinder. While Pendry initially conceived of the invisibility cloak as a theoretical exercise to highlight the potential of metamaterials, he later expressed skepticism about realizing large-scale, flexible cloaks akin to those in fiction. He acknowledged the possibility of hiding centimeter-sized objects from light but emphasized the practical limitations.
In 2009, researchers at Bilkent University in Turkey announced in the New Journal of Physics that they had achieved practical invisibility using nanotechnology. They claimed to have created a nanotechnological material that could render an object invisible with no shadows, presenting a near-perfect transparent scene. They even suggested the possibility of producing this material in the form of wearable suits
More recently, in 2019, Hyperstealth Biotechnology patented a technology called Quantum Stealth, a material designed to bend light and make people and objects nearly invisible to the naked eye. Developed primarily for military applications by the company's CEO, Guy Cramer, this material is still in the prototype phase. Unlike traditional camouflage, Quantum Stealth reportedly works in any environment or season and at any time of day, although its application requires artificial backgrounds with horizontal lines..
Nice👍
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