The Expanding Universe

Activity:
Using balloons to model the expansion of the Universe

Science Standards:
Nature of Science, Patterns of Change, Scientific Models (Scale & Conceptual)

Objectives:

  • The student will create a dynamic model of the Universe.
  • The student will observe a varied recessional velocity of galaxies.
  • Materials:

  • balloons
  • cotton balls
  • rubber cement
  • markers
  • straight metric ruler or meter stick (not a tape measure)



  • Introduction:
    This Big Bang Theory is the result of several important observations. First, Edwin Hubble observed in 1927 that galaxies are red shifted; galaxies are becoming farther and farther away from us. Second, he determined that the farther away a galaxy is, the faster it is receding. If the universe is expanding, then one can assume that the galaxies that compose our universe were once much closer together than they are now. By simply measuring how far apart galaxies are and how fast they are moving, we determine what cosmologists call the Hubble Constant (which likely ranges from 50 to 100). It is very easy to determine the recessional velocity of galaxies; on the other hand, their current position is difficult to measure. Distances to galaxies are typically measured by finding Cepheid variable stars or supernovae with known brightness. IF we run the expansion process backward we get two results. The first result is that it probably took on the order of 15 billion years for the Universe to grow to its present size. Second, some awesome event must have caused the galaxies to go flying away from one another. Scientists don't know what exactly this phenomena could have been, but astronomers refer to it as the Big Bang.

    Directions:
    1. Partially inflate the balloon to a 10 cm diameter.
    2. Cement four cotton balls around the balloon to represent galaxies.
    3. Mark one as our home galaxy (the Milky Way).
    4. Measure and record the distance from home to each galaxy.
    5. Fully inflate the balloon without bursting it.
    6. Measure and record each distance again.
    7. Complete the student answer sheet questions.

    The Expanding Universe - Student Answer Sheet

    Description: You will model an expanding universe.

    Materials:

  • one balloon for each student
  • several cotton balls
  • rubber cement
  • rulers or meter sticks
  • Introduction:
    The spectra of all galaxies exhibit a red shift . What does this imply about where our galaxy, the Milky Way, is located in the universe?
     
     
     
     
     

    Procedure:

    1. Slightly inflate your balloon to a diameter of approximately 10 cm.

    2. Using several small bunches of cotton, attach four cotton balls all around the balloon with rubber cement.

    3. Choose one galaxy to represent our own and mark it with a pen. Then measure the distance to from our galaxy to three of the other galaxies.
     
     

    distance to galaxy 1: ___________________ cm
     
     

    distance to galaxy 2: ___________________ cm
     
     

    distance to galaxy 3: ___________________ cm
     

    4. Slowly inflate the balloon. DO NOT ALLOW IT TO BURST!

    5. Again measure the distance from the Milky Way to the previously chosen galaxies.

    new distance to galaxy 1: ___________________ cm
     
     

    new distance to galaxy 2: ___________________ cm
     
     

    new distance to galaxy 3: ___________________ cm

    6. Are all galaxies moving away from us at an equal rate? Which ones are moving away fastest?
     
     

    7. Accurately measuring the distances between the galaxies is obviously difficult. It is for astronomers too. How might this difficulty affect our understanding of the universe?
     
     

    8. How could you determine the velocity at which a galaxy is moving away?
     
     
     

    8. Discuss what will happen if the universe expands forever. What if it does not expand forever?
     
     

    9. Describe what you think the theory of the oscillating universe might be?
     
     
     

    10. Why might astronomers care to determine the rate at which the universe is expanding?