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The Big Bang Theory: Explanation and Evidence

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  • 0:04 The Beginning of Time
  • 0:56 Hubble's Law
  • 2:03 The Big Bang
  • 2:51 Quantum Physics
  • 3:35 Lesson Summary
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Lesson Transcript
Instructor
Lisa Roundy

Lisa has taught at all levels from kindergarten to college and has a master's degree in human relations.

Expert Contributor
Matthew Bergstresser

Matthew has a Master of Arts degree in Physics Education. He has taught high school chemistry and physics for 14 years.

A popular scientific theory is that our universe originated with what is known as the Big Bang. This lesson explains what the Big Bang is and the evidence that supports it. Following the lesson, you can test your newfound knowledge with a quiz!

The Beginning of Time

When we look around at our surroundings as kids, many of us wonder how everything around us came into being. Trust me: this continues on all throughout adulthood and is why we have certain scientific fields!

Rarely the knowledge of what exists is enough to satisfy us, and we want to know how and why everything exists. These aren't easy questions to answer, and we may never know the answers with absolute certainty. However, we've learned a lot about the laws of nature in our quest for this knowledge. The laws of nature govern all things in the universe from the direction and speed a ball bounces to the way the planets move in their orbits. Our increased understanding of these laws over time eventually led us to describe an event known as the Big Bang, which is the idea that the universe began at a single moment in time with an intense burst of energy.

Hubble's Law

In order to understand the Big Bang, we need to begin with the discovery that started it all. The name Edwin Hubble may sound familiar to you, probably because of the famous Hubble telescope. Hubble didn't build the telescope, but it was named after him. One thing you may not know is that the foundation for the concept of the Big Bang theory comes from one of Hubble's discoveries: Hubble found that galaxies are moving away from us! He also found that this appears to occur at speeds proportional to their distance and that it's occurring in all directions. In other words, he observed that the universe is experiencing an ongoing process of expansion. This observation has come to be known as Hubble's Law.

The idea of expansion as explained by Hubble's Law supports the idea that the universe was once compressed into a much smaller space. Hubble's Law was used to develop a new theory of the creation and expansion of the universe that eventually came to be known as the Big Bang. Over time, the Big Bang theory has been modified and adapted, and the future will likely hold more adaptations as our understanding of the universe increases.

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Additional Activities

Modeling the Universe


A model is a way scientists take something very large or very small and put it into a size that is easy to study or manipulate. The universe is enormous, so we will make a model of it using a balloon and a sharpie. Here are the steps to take to model our universe.


  1. Take a balloon that will blow up into a roughly spherical shape. (The universe isn't spherical, but that's alright. Models sometimes are not completely true to reality, but they help us learn about the concept anyway.) Use the Sharpie marker to put dots on the balloon fairly close together. Try to put at least 20 dots on the balloon.
  2. Measure the distance in millimeters between five dots. Record these distances.
  3. Start to blow up the balloon about one-quarter of the size of the final size. Measure the distance between the same dots you did in step 2. Record the new distances between the dots.
  4. Blow up the balloon to about one-half of the size of the final size. Measure the distance between the same dots you did in step 2. Record the new distances between the dots.
  5. Blow up the balloon to about three-quarters of the size of the final size. Measure the distance between the same dots you did in step 2. Record the new distances between the dots.
  6. Blow up the balloon to the full size. Measure the distance between the same dots you did in step 2. Record the new distances between the dots.


Follow up questions


1. If the dots represent galaxy clusters what does the balloon represent?

2. What happened to the distance between the dots as the balloon was blown up?

3. Did the distance between the dots increase more when the balloon was just starting to expand or when the balloon got larger and larger?

4. The universe is three-dimensional, the dots on the balloon get larger when the balloon is blown up and outside the edge of the universe contains nothing. Think of three ways this model of the Big Bang theory is inaccurate.

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