# Cosmic Microwave Background Radiation Lesson for Kids

Instructor: Suzanne Rose

Suzanne has taught all levels PK-graduate school and has a PhD in Instructional Systems Design. She currently teachers literacy courses to preservice and inservice teachers.

Some of the most important scientific discoveries and inventions have happened by accident. In this lesson, you'll learn how the Cosmic Microwave Background was discovered accidentally, with the help of pigeons!

## Is It the Pigeon Poop?

Two scientists working in their laboratory in 1965 were frustrated because they kept hearing noises in the radio receiver they were building. A radio receiver picks up radio waves from the air. They tried everything to fix it, but the noise was still there.

The scientists, Arno Penzias and Robert Wilson, noticed that there were pigeon droppings on the antenna they were using. Maybe the pigeon poop was causing the interference! The scientists got a bird trap and caught the pigeons, then cleaned the pigeon droppings from the antenna. Even after all this work, the noise was still there!

When Penzias and Wilson finally realized what they were hearing, they were very excited. They'd found something they weren't looking for, but it was something for which other scientists had been searching for over twenty years: evidence of how the universe was created.

## The Big Bang

Penzias and Wilson found the Cosmic Microwave Background, or CMB, for short. Let's explore what the CMB is and what it has to do with the origins of the universe.

The Big Bang Theory is one explanation scientists use to describe how our universe started. According to this theory, the universe began to expand and get bigger about 14 billion years ago. At first, it was just one-hundred-millionth the size it is now and everything in it was tightly packed together.

At that time, the universe was very, very hot. As you might know, heat is a type of energy that travels in waves. This heat energy was released into the universe as the universe formed. The CMB is actually what's left of the heat left over from the Big Bang.

## Where Is the CMB?

Scientists who believed the Big Bang Theory looked for the CMB for many years. They knew that if their theory about how the universe was formed was correct, the CMB had to be out there somewhere. There had to be radiation left over from the Big Bang. Why couldn't they find it?

As we said before, the CMB is made up of waves traveling through the air. These waves are in the microwave part of the electromagnetic spectrum, which means they're invisible to humans.

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