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What is the Big Bang?

Recall how previouslyyou learned that using the Doppler Effect will help determine if a red shift or a blue shift is occurring with respect to stars. This activity is designed to help you see how the red shift provides the opportunity to model the Big Bang theory as it relates to the red shift.


  • Large latex balloon
  • Permanent marker
Safety concerns: As with all science lab activities, the most important safety rule is to follow all teacher directions.
  1. Blow up the balloon until it is about 10 centimeters (4 inches) in diameter.
    • Do not tie the end.
    • Have a partner mark six dots scattered around the surface of the balloon.
    • Label one of the dots as "MW," to represent the Milky Way Galaxy.
    • The other dots represent other galaxies throughout the universe.
  2. Without letting any air out of the balloon, blow more air into the balloon until the diameter is approximately 5 cm larger.
    • Observe the change in the location of the dots relative to each other.
  3. Repeat the process, this time blowing up the balloon so that it is another 5 cm larger.
  4. Now blow up the balloon so that it is almost as full as it can go. DO NOT POP IT. Repeat your observations.
Watch the QuickTime movie below to see how the dots move away from the Milky Way (MW) as the balloon (universe) expands.


  1. If you were standing at the point labeled "MW," what kind of shift would you expect to see in the spectra of the dots representing other galaxies?
  2. Why are color shifts important in understanding what is happening to the universe?
  3. Imagine that you didn't see the the balloon start expanding; butyou then witnessed the balloon continue to expand, what could you infer about the size of the balloon before you began watching?
  4. How does the expansion of the balloon relate to the expansion of the universe?

Hubble's explaination of the expanding universe.

When Hubble noticed all of the red shifts compared to the very few blue shifts, he realized that the universe is expanding. Just as you did during the balloon analysis, scientists can now point to what the universe must have looked like in the past if we are currently watching it expand. Remember our loaf of raisin bread. If you walked into the kitchen and observed that the bread had been rising, what could you say about what the loaf looked like 15 or 20 minutes ago? The same thing happens with the universe. As we watch the universe get larger, we can say that at some point in time, the matter and energy that forms the universe must have been much closer together. What could have sent all of that material flying outward into space? Only an explosion beyond anything we have ever seen could have done that.

This explosion is known as the big bang, and is generally referred to as the beginning of the universe. At a certain time in the past, all matter and energy was found in one spot. Over 13 billion years ago, the big bang sent that matter and energy exploding outward, and the universe began. If the universe is truly expanding, then that means that at some point in time, all of the matter must have been together, just as in the balloon analysis.

Review science lab safety rules here.

Get the plug-ins: Get Adobe Acrobat Reader and Get Quicktime Player. (The QuickTime plug-in is needed to play sounds and movies correctly.)

Want to share photos of you or your friends doing this activity? Send it in an e-mail with the following information:

  1. The title of the activity
  2. The URL (Internet address)
  3. Your name.

Remember that no pictures can be used that show student faces or student names on it. 

Teachers should view the Teacher Site Map to relate Sci-ber text and the USOE Earth Systems Science core.


Updated October 24, 2008 by: Glen Westbroek

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