Radiation From Within

Hello reader,

Can you classify the Sun and a steel ball in the same category? What do you think? I think so. I know the Sun isn't metalic, but it is shiny... right? Right? Historically, this is the mother of Quantum Physics. The very beginning. Plank did well.

Anyways, the Sun and the steel ball can be categorized as... A Black Body! Do think of it the wrong way, think of black body as a scientific object. Let's dissect the word first, then we can check other fun properties.

Black: it's a shade in our "colour" scale that as my grade 8 art and grade 9 science teachers put it, "Absorb all light". White is different. It reflects all light. So if a perfectly black object absorbs all light, it is unable to reflect any light. Using this defintion of black, we can then define Black Body as an object that absorbs all light directed at it without emitting any light back (reflecting light).

The Sun can be considered a black body (Before I go any further, there is no such thing as a perfect black body in our known universe. There is only what we can approximate to be black bodies.). But you ask, why are we able to see white light emitted? This is what puzzled physicist Maxwell Plank. Not only that but with old models, we would have the Ultraviolet Catastrophe. So what changed?

Maxwell looked at the Sun (not for very long though) and thought that maybe what is being seen, was thermal energy. Energy, in the form of heat, was being converted to electromagnetic energy (light). So he figured out that the old models were wrong, and that his new formula and idea of light packets (or quanta) would help explain the empirical (experimental) data (as shown in the picture).

This new model indicated that at certain temperatures, there was a maximum intensity for a given wavelength. As the temperature increases, the maximum intensity of the wavelength increases. If you take the integration of this curve, you get infinity. The area under the curve is the energy per unit volume.

This was the problem with the old model. When you integrated the curve from 0 to infinity (wavelengths) it would say that you get infinite energy! Most of this energy was in the ultraviolet spectra. This was cause for concern! How could something forever be emitting UV radiation. This did not get picked up by health critics because they did not know of the adverse affects of UV radiation at the time.

So in all, a black body is something that emits thermal energy in the form of light and light like radiation. Oh and by the way... The steel ball, it is considered a black body at about 1000 K or 1273 degrees Celsius.

See and Be Seen

Hello Reader,

As a society that really wants to be seen, make a scene and individuals wanting to be noticed for something, we seem to be putting a bit of effort for the opposite! Ever wonder if not being seen is possible? Reader, I'm talking about invisibility. Using a device to hide oneself from other people's vision. Kind of like the Invisibility Cloak from Harry Potter.

*key idea: you need 2 main things for vision to occur. Object to be seen and an observer. Without either one, nothing can be seen*

For invisibility to work, the material being used must not be seen by the observer. As shown in the picture to the right, the material has to be able to reflect of the material, hit another above the object and bounce off the back. Unfortunately, this is very hard and maybe even impossible to do (have something follow you from above).

Let's take a step back for a second though. Light is an electromagnetic wave (we also know now, that it is a particle). That is, it changes from an electric field to a magnetic field very quickly. We know this thanks to James Maxwell. He also had thoughts about invisibility.

We know that most liquids and gases are "invisible" (transparent), but why is that? Atoms in higher excited states (due to heat, pressure or a bigger volume) have more spaces between them. This is a key role for such visibility problems. If the spaces between the atoms are greater than the wavelength of the light, then light is not given off. What about diamonds? Why can I see right through them? Some solids have special properties.they are called Lattices'. The atoms are arranged so that there are equal spaces between each other and is organised!

So how do we use such properties to become unseen? New materials are being worked on in laboratories called Metamaterial. These are materials that can bend light waves. So far, we are able to bend microwaves (smaller than infrared).

Light have a property called the index of refraction. If you have ever gone fishing and saw a fish in the water and decided to put a net over the fish, you know that you didn't catch it. this is because the index of refraction is responsible for the bending of light. This concept needs to be applied to an invisibility device. Metamaterial is special, in which it actually has a negative value for the index of refraction (everything you can see will always have a positive value).

This is quite close to the concept of Fibre Optics. In a fibre optic tube, light is bent at a 90 degree angle so nothing passes through it but stays contained in the tube. The US military has a device that uses fibre optics for an "invisible" cloaking device. this is the closest we are to such a cloaking device.

In Michio Kaku's book, Physics of the Impossible, he rates invisibility a class 1 impossibility. This means that it is not possible now, but will be in a matter of a decade.