What is the cosmic microwave background radiation? Was it created after the Big Bang?

What is the cosmic microwave background radiation?

The creation and discovery of cosmic microwave background radiation

The cosmic microwave background (CMB) is the oldest and longest-traveling light we can see in the entire universe. (Photo source: Yaroslav Vitkovskiy/Shutterstock)

This article first appeared in The Conversation, which licensed it to Space.com's Expert Voices: Op-Ed & Insights.

What is the cosmic microwave background radiation? Was it created after the Big Bang? -Sreehari, 9, from Kerala, India

The Cosmic Microwave Background (CMB) is the oldest and farthest-traveling light we can see in the entire universe. It was created soon after the Big Bang (the beginning of the universe).

However, it's not the kind of light you or I can see with our eyes. The light we can see is called visible light, but there are other types of light as well. Microwaves are one type of light, as are the X-rays we use to check for broken bones and the radio waves we use to listen to music in our cars.

Initially, the CMB was also very energetic X-rays, but over time it gradually lost energy and became lower-energy microwaves.

The CMB is light that has been there since the birth of the universe, when it was very hot and dense, filled with electrons and protons. These particles have an electric charge, and when light hits one, the charge sends the light in another direction. This prevents the light from traveling very far.

A photo of the CMB taken by the Planck telescope. The colors represent the different temperatures at different locations of the CMB. (Image source: ESA and Planck Laboratory, CC BY-SA)

Cool down gradually

As time went by, the universe expanded and gradually cooled. Eventually, after cooling to a certain point, electrons and protons combined together to form hydrogen atoms. These atoms have no charge, so they do not affect the propagation of light in the same way as electrons and protons. Light can pass through them and propagate through the universe as if the universe were empty.

The universe was cooling at the same rate everywhere, and the process was happening everywhere at the same time. Suddenly, light could travel very fast and long distances all over the universe at the same time. Light is still traveling today, and the light that reaches Earth is the cosmic microwave background.

Before the first atom was created, CMB light was all over the universe but couldn't travel very far. In fact, we know it was released only 380,000 years after the Big Bang, which sounds like a long time from the Big Bang to the release of light, but compared to the age of the universe, which is nearly 14 billion years old, it actually happened when the universe was still very young.

The CMB tells us a lot of important information, like how old the universe was. According to the Big Bang theory, the early universe was very hot and full of radiation. As the universe expanded and cooled, this radiation was eventually released into the CMB we see today. The Big Bang theory even makes predictions about the temperature of the universe, which is why we use the CMB as evidence that the Big Bang theory is correct.

An unexpected discovery

The CMB was discovered by accident. Two scientists, Robert Wilson and Johannes Penzias, noticed that when they used a microwave telescope to observe the same external signal no matter how they moved the antenna, and they thought that the signal might be caused by the telescope itself - or even by pigeon droppings on the antenna.

The Holmdel 15-meter horn antenna at Bell Telescope Laboratories in Holmdel, New Jersey, was used by radio astronomers Robert Wilson and Arno Penzias when they discovered the CMB. (Image credit: NASA via Wikimedia Commons)

Eventually they realized they were the first to detect the CMB, which had been predicted by the Big Bang theory. They won a Nobel Prize for it.

Since then, we've sent many telescopes into space and obtained increasingly precise images of the CMB. Observing the oldest light in the universe helps us understand many of the things we see today.

BY:Christopher Pattison

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