The Cosmic Microwave Background

In my previous post, I had discussed about the origin of the universe in the extraordinary event called the Big Bang. This post mainly deals with what astrophysicists call the Cosmic Microwave Background. They are ancestors of photons from the eons in which decoupling took place. The photons we see after the time of decoupling event in the universe form a part of the Cosmic Microwave Background.

After the Big Bang, the universe slowly began to cool. This led to the formation of hydrogen and helium. At redshifts under 1000, the universe was bubbling with ionized hydrogen atoms. Ionized hydrogen atoms were formed when photons knocked askew the electrons of the hydrogen atoms. These ionized hydrogen atoms scattered light all around the universe such that the universe became a glowing fog – a fog of immensely hot, charged particles moving rambunctiously across the universe. As the universe cooled further, electrons and ions reconciled to form neutral atoms of hydrogen and helium. This made the universe transparent, which means the photons are free to move. This event is termed as decoupling.

The photons emitted from this period of decoupling form a part of the Cosmic Microwave Background. While a heating object glows, it emits light in all parts of the spectrum, but peaks in a particular part. Obviously, the Cosmic Microwave Background had a spectrum that peaked in the microwaves.

As the universe continues to cool, this ‘peak’ is slowly shifting to radio-waves. If humanity persists on Earth for another 50 million years, these waves might be called Cosmic Radio-wave Background.

Let us indulge into the history of Cosmic Microwave Background. In 1964, working for the Bell Telephone Laboratories, Arno Penzias and Robert Wilson developed a horn-shaped antenna for detecting microwaves under the authority of Bell Telephone Laboratories.

Why did a telephone company decide to invest in astrophysics? Well, the answer is simple – they didn’t. They were simply trying to send and receive signals in an efficient manner. If a telephone company wishes to signals better, they have to get rid of outside network or sources that interfere with the transmission of data.

Penzias and Wilson worked for a company that wanted to get rid of these microwave interferences for their receiver.  They wanted to do this to eradicate such signals and establish a better means of communication, where users participated in noise-free communication.

When Penzias and Wilson subtracted their data from all terrestrial and cosmic source of interference known to the world at that time, one part refused to leave. The two wondered what it might be and discovered that inside the dish existed pigeon poop (blame those pooping pigeons for adding an extra chapter to your physics books!). The dielectric signals from the poop were thought to be responsible. After cleaning the dielectric poop, interference dropped a little but a signal still remained.

Later, this was found out to be the Cosmic Microwave Background. Some parts of this Cosmic Microwave Background are slightly hotter than the average values of temperature and some slightly cooler.  These temperature variations aid in interfering the structure of the matter in early universe. This also helps calculate the strength of force of gravity at that time.

Let us now go one notch higher and focus on a convoluted definition of our topic. Cosmic Microwave Background is an emission of uniform, black body thermal energy coming from everywhere in the sky. A black body absorbs all incoming electromagnetic radiation like light. What is black body radiation? It is the numerous kinds of electromagnetic radiation emitted by a black body. Cosmic Microwave Background’s intensity is uniform from all directions and does not change. It is a kind of black body radiation. Hence, wherever you look in the sky, the intensity of black body radiation from the Cosmic Microwave Background remains the same.

How does the Cosmic Microwave Background serve as a proof for Big Bang? Well, if the universe has a temperature deep in space, it will have energy too. Where does this energy come from? The answer is simple – the Big Bang!

Are there any other achievements of the Big Bang Theory? Are there any other failures? Keep reading!!! And continue to speculate, innovate till you constipate!

One thought on “The Cosmic Microwave Background

  1. These ancient photons actually peaked in ridiculously high frequencies (tiny wavelengths) and over billions of years redshifted to what we see now as microwave length light.


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