Invisibility has always been the center element of many fictions and mythology. Harry porter had a magical cloak which let him wander around the Hogwards undetected. In lord of the Rings trilogy, the ring gave the power to become invisible. In Avengers: Age of Ultron, they had a ship which could turn invisible and be undetected. There are tons of cases of invisibility which we have seen in movies, read in novels and heard in mythological stories. What if we could become invisible at our own will??
Let’s ignore the fiction and explore the science behind it……
Before knowing the science behind invisibility, we need to understand ……
How do we see things?
It is simple high school science behind visibility. When light falls on an object, it gets reflected everywhere all around. The reflected light rays which fall on our eyes, give our eyes the sensation of visibility. The similar science is behind invisibility. If we succeed in bending the light rays such that it doesn’t fall on the object, then the object would become invisible.Such material is not present in nature. We need to design it according to our need. Such type of material is called metamaterial.
Metamaterial
Metamaterials are the materials whose optical properties are not found in nature. These are designed in lab for special purposes. In 2006, scientists at Duke university, designed metamaterials which became invisible to microwave radiation. The wavelength of microwave radiation is very large compared to visible light. We can’t see microwave radiation. But this discovery is a great achievement towards invisibility. If scientists are successful in imitating the same thing for visible light, we can make things invisible to our eyes. One obvious question should be how metamaterials can make things go invisible?
Metamaterials bend the electromagnetic (i.e. light wave) waves, so that it passes from the object without reflecting light. If metamaterials are able to eliminate reflection of light from the object, then it would become invisible to our eyes.
One important concept that can help in invisibility process is called Negative Refractive Index. Let us understand first what is Refractive Index. We know that the speed of light is different in different mediums, based on this knowledge we define Refractive Index. It is the ratio of the speed of light in vacuum to the speed of light in that medium. Usually refractive index is positive and greater than one.
Light upon changing the medium gets refracted. If for some reason light, instead of refracting, gets reflected than the medium is said to have negative refractive index. This is the phenomena in which light rays show different behavior than expected.
The diagram shows the effect of having negative RI.
Negative index materials have properties opposite to those of glasses, air and other such materials. Normally when light travels from air to water it bends away from the normal (line perpendicular to the plane in which light Travels). In contrast, when light travels from air to the negative index material would not bend towards or away from the normal rather go in some different direction.Another method to make things go invisible is to use nanotechnology.
Nanotechnology
The reason why digital devices are getting better and that too without increasing in size is because we use Nanotechnology. The use of Photolithography has made possible to insert over 100 million of transistors in just the space of the size of our thumb. To make things go invisible we need to design the size of each particle to be smaller than the wavelength of light.
By doing so the light wouldn’t reflect from the object, instead pass through it and hence that object would become invisible to our eye. To alter each and every particle is difficult. But scientists are trying very hard to make it possible. In 2007, scientist of Germany and US department of energy prepared a metamaterial that was invisible to red light (light with longest wavelength in visible range). This is a step closer to the invisibility seen in movies.
Plasmonic
To alter the structure at atomic level is way tough, so scientist have come up with an alternative option too. It is called Plasmonic. It allows to squeeze light so that objects can be manipulated at atomic scale. Scientists have designed a Plasmonic Cloak which creates the effect of. invisibility It basically works on the principle of destructive interference. The scattered light from the metal and semiconductor cancel each other and
hence create a sensation of invisibility. Though this technique is not universal but still it has proved to be useful in its domain.
Invisible Cloak
An invisible cloak is being prepared, somehow like the magical cloak of harry porter. The principle behind it is called optical camouflage. Research on it is conducted by Naoki kawakami. HOW DOES IT WORK?
Basically, it clicks the picture of the background and projects it on the front of the cloak. It is covered with tiny light reflective beads. It is wrap around the thing to be made invisible. It takes picture from the behind and projects it on the front. The thing appears to get disappeared. The problem with it is that, when you look at it from different angles, the image does not appear to be moving. Hence, we can say that it is fake. In order to encounter this problem 3D images should be used. The 3D holograms can be created by using laser light. The background scenery is captured by special holographic camera and that image is projected from the front on the screen. This makes the person invisible and the 3D image makes it look real.
However, there are few challenges in this method. Firstly, we need to create a holographic camera that takes 30 images per second, which is too many images in a second. Secondly, storing and processing this information is bit tough. Thirdly, there need to be a projecting device at the front side which can project image on the screen.
4th dimension
One more method is there which can help us attain invisibility, 4th dimension. This might sound crazy but let me tell you string theory and M-theory have predicted the presence of 11 and 26 dimensions, respectively. How can 4th dimension make something invisible?
Let me answer this question by giving an example. Everybody must have played video games, right? Let’s say you play PUBG in your mobile. You are a 3-dimensional being but your mobile is a 2-dimensional device. Now imagine the virtual game characters in your game are just real like us. You can control everything happening in the game but can your mobile game character talk to you or see you? NO, because they are 2-dimensional and we are 3-dimensional. So, technically you are invisible to the characters in the game. The same is the logic behind 4th dimension making you invisible. If, somehow, we unlock the way to access 4thdimension we could become invisible to other beings on earth who live in 3 dimensions.
If we succeed in making things go invisible, we would make it work in many sectors: -
• Cure baby in the womb
• Strengthen our defense system by making our fighter jets, soldiers, etc. go invisible.
• We can take photo of the DNA and human cell
These were some of the methods which can make humans go invisible. Some methods are tough to be practical but some of them have become reality. Invisibility can do wonders and destructions too. Its totally on us how we use it. Scientists have claimed that they will make invisibility possible within this decade. Everything seems crazy and impractical before it becomes reality. This is how science works.
Keep it up brother.
ReplyDeleteGoing very well.